Durham E-Theses
Some studies in step-growth photoreductive
polymerizations
Batey, Jonathan Wilson Urquhart
How to cite:
Batey, Jonathan Wilson Urquhart (1978) Some studies in step-growth photoreductive polymerizations,
Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/9033/
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SOME STUDIES IN STEP-GROWTH
PHOTOREDUCTIVE POLYMERIZATIONS
A t h e s i s s u b m i t t e d f o r t h e degree o f Master o f Science
by
Jonathan W i l s o n U r q u h a r t Batey, B.Sc. (Keele)
(Graduate S o c i e t y )
UNIVERSITY OF DURHAM
1978
The copyright of this thesis rests with the author.
No quotation from it should be published without
his prior written consent and information derived
from it should be acknowledged.
ti
TO MY PARENTS
n i
SUMMARY
T h i s t h e s i s d e s c r i b e s some s t u d i e s I n t h e area o f s t e p - g r o w t h
photoreductive polymerization.
The monomers used were m e t a - d I b e n z o y l benzene and meta - and
para - b l s b e n z h y d r o l s .
Equimolar m i x t u r e s o f d I ketone and d l o l
were I r r a d i a t e d under a v a r i e t y o f c o n d i t i o n s i n an a t t e m p t t o
a t t a i n t h e optimum degree o f p o l y m e r i z a t i o n f o r t h e p r o d u c t
polypinacols.
The
p o l y p i n a c o l s o b t a i n e d were isomer!zed t o p o l y p i n a c o l o n e s ,
which were reduced and then d e h y d r a t e d
a t o t a l l y c o n j u g a t e d system.
I n an a t t e m p t t o s y n t h e s i z e
T h i s a s p e c t o f t h e work was o n l y
p a r t i a l l y s u c c e s s f u l and t h e problems encountered
the
l a s t chapter o f the t h e s i s .
are discussed I n
Iv
I would l i k e t o t h a n k Dr. W.J.
Feast f o r h i s encouragement
and u n f a i l i n g s u p p o r t t h r o u g h o u t t h e s u p e r v i s i o n o f t h i s work.
I am Indebted t o a l l t h e t e c h n i c a l and l a b o r a t o r y s t a f f f o r
t h e i r c o n s t r u c t i v e a d v i c e and a s s i s t a n c e , as w e l l as t o t h e s t a f f
and p a r t n e r s o f Mann Judd.
V
MEMORANDUM
The work o f t h i s t h e s i s was c a r r i e d o u t I n t h e C h e m i s t r y
L a b o r a t o r i e s o f t h e U n i v e r s i t y o f Durham between October
and September 1978.
T h i s work has n o t been s u b m i t t e d
o t h e r degree and I s t h e o r i g i n a l work o f t h e a u t h o r
where acknowledged by r e f e r e n c e .
1977
f o r any
except
CONTENTS
Page
Summary
111
Acknowledgements
Iv
Memorandum
v
CHAPTER 1
STEP GROWTH PHOTOPOLYMERIZATION
1.1
Introduction
1
1.2
Polymer C l a s s i f i c a t i o n
1
1.3
Polymer Growth Mechanisms
2
a)
Chain-Growth P o l y m e r i z a t i o n
2
b)
Step-Growth P o l y m e r i z a t i o n
3
1.4
Photopolymerlzatlon
5
1.5
Some Examples o f Step-Growth
Photopolymerizatlon
7
a)
b)
c)
Photopolymerizatlon via the Singlet
State
7
Photopolymerization via the T r i p l e t
State
9
Photopolymerization v i a a Reactive
I n t e r m e d i a t e Formed I n an I n i t i a l
Photochemical Process
11
CHAPTER 2
PHOTOREDUCTIVE POLYMERIZATION
2.1
Photochemical Processes
2.2
The Carbonyl Chromophore
2.3
P h o t o r e d u c t i o n o f Carbonyl Compounds
15
2.4
Photoreductive Polymerization
19
a)
b)
12
14
E a r l y r e s u l t s on p h o t o r e d u c t i v e
polymerizations o f diketones
20
R e s u l t s o f De Schryver and co-workers
on t h e p h o t o r e d u c t i v e p o l y m e r i z a t i o n
of diketones
25
2.5
O b j e c t i v e s o f Present Research
CHAPTER 3
SYNTHESIS OF MONOMERS. THEIR PHOTOPOLYMERIZATION
AND SUBSEQUENT REACTIONS
PART 1
MONOMERS
33
3.1
The F r l e d e l C r a f t s Reaction
33
3.2
Grtgnard
34
Reagents
29
Page
3-3
3.4
Sodium B o r o h y d r i d e Reduction o f meta D l b e n z o y l benzene
36
Experimental
36
a)
b)
c)
P r e p a r a t i o n o f m-dIbenzoylbenzene
(Frledel Crafts)
Preparation o f l , 3 - b l s ( hydroxybenzyl)
benzene
Preparation o f l , 4 - b l s ( hydroxybenzyl)
benzene ( G r l g n a r d r o u t e )
36
37
38
PART 2
POLYMERIZATIONS
39
3.5
P r e p a r a t i o n o f t h e S o l u t i o n s t o be
Irradiated
39
3.6
P h o t o r e d u c t l o n o f m-DIbenzoylbenzene I n
Benzene : Isopropanol M i x t u r e s
I)
II)
43
Experimental
43
M o l e c u l a r Weights o f t h e P o l y b e n z o p l n a c o l s
Prepared I n Benzene : Isopropanol
44
PART 3
REACTIONS OF POLYBENZOPINACOL
3.7
The D e h y d r a t i o n o f Polybenzoplnacol
3.8
Reduction o f Polymer X and/or U
3.9
D e h y d r a t i o n o f Polymers X I I and/or
PART 4
CONCLUSIONS AND SUGGESTIONS FOR FURTHER WORK
51
APPENDIX A
Apparatus and Instruments
53
APPENDIX B
I n f r a r e d Spectra
54
REFERENCES
48
(UJa)
48
50
TTTT
50
59
CHAPTER I
STEP-GROWTH PHOTOPOLYMERIZATION
1.1
INTRODUCTION
In t h i s c h a p t e r t h e c o n t e x t and o b j e c t i v e s o f t h e work t o be
described subsequently are s e t out.
I t seems a p p r o p r i a t e t o s t a r t w i t h
a b r i e f d i s c u s s i o n o f t h e c l a s s i f i c a t i o n o f polymer f o r m i n g r e a c t i o n s and
the
a s s o c i a t e d t e r m i n o l o g y , s i n c e t h e process o f c l a s s i f i c a t i o n has
p l a y e d an i m p o r t a n t r o l e i n c l a r i f y i n g o u r u n d e r s t a n d i n g o f t h e s u b j e c t
and t h e t e r m i n o l o g y used I n t h i s area has been t h e s u b j e c t o f r e c e n t
redefinition.
1.2
POLYMER CLASSIFICATION
In 1929, C a r o t h e r s ' f o r m u l a t e d t h e . f i r s t
i m p o r t a n t though
rather
g e n e r a l c l a s s i f i c a t i o n o f polymers and polymer f o r m i n g r e a c t i o n s .
classified
He
t h e s u b j e c t i n t o two broad s e c t i o n s , a d d i t i o n p o l y m e r i z a t i o n s
l e a d i n g t o a d d i t i o n polymers and c o n d e n s a t i o n p o l y m e r i z a t i o n s l e a d i n g t o
c o n d e n s a t i o n polymers.
In t h e former process t h e p r o d u c t s have
r e p e a t i n g u n i t s c o n t a i n i n g t h e same number and sequence o f c o n s t i t u e n t
atoms as t h o s e o f t h e monomers and t h e polymer m o l e c u l a r w e i g h t
a s i m p l e summation o f t h e monomer m o l e c u l a r w e i g h t s .
(M) i s
Condensation
polymers, on t h e o t h e r hand, have r e p e a t i n g u n i t s c o n t a i n i n g
fewer
atoms than t h e monomers f r o m which t h e polymer was formed and
c o n s e q u e n t l y M f o r t h e s e p r o d u c t s i s less t h a n t h e sum o f m o l e c u l a r
w e i g h t s o f t h e r e a c t i n g monomers.
The s h o r t c o m i n g o f Carothers c l a s s i f i c a t i o n a r i s e s f r o m t h e f a c t
t h a t polymers h a v i n g t h e same chemical s t r u c t u r e may be made v i a e i t h e r
r o u t e , and t h e p h y s i c a l p r o p e r t i e s o f t h e r e s u l t i n g
t o be independent o f t h e t y p e o f p o l y m e r i z a t i o n .
polymers
a r e found
For example,
p o l y m e t h y l e n e formed by a Wurtz r e a c t i o n f r o m 1,10 - dtbromodecane
( c o n d e n s a t i o n p o l y m e r i z a t i o n ) Is a low m e l t i n g wax whereas samples o f
p o l y m e t h y l e n e formed by t h e copper c a t a l y s e d d e c o m p o s i t i o n o f
dlazo-methane
(condensation) o r the p o l y m e r i z a t i o n o f e t h y l e n e
(addlti
3
both y i e l d the f a m i l i a r p l a s t i c m a t e r i a l , polyethylene .
Several
o t h e r examples o f t h e same t y p e a r e known and t h e s e o b s e r v a t i o n s l e d
t o a r e c o n s i d e r a t i o n o f polymer c l a s s i f i c a t i o n s .
of
polymer c l a s s i f i c a t i o n has been d i s c u s s e d a t l e n g t h by Lenz
advocates
the
The whole s u b j e c t
a c l a s s i f i c a t i o n based on t h r e e c o n s i d e r a t i o n s .
who
Firstly
add i t i o n / c o n d e n s a t i o n c l a s s i f i c a t i o n o u t l i n e d above, secondly
whether t h e polymer c h a i n grows by a s t e p - g r o w t h o r c h a i n - g r o w t h
process and t h i r d l y t h e e f f e c t i v e n e s s o f t h e process as measured by
the
h i g h o r low m o l e c u l a r w e i g h t a t t a i n e d .
Three c r i t e r i a ,
h a v i n g two o p t i o n s leads t o e i g h t main c l a s s e s .
each
The i m p o r t a n t p o i n t
emphasised by t h i s new c l a s s i f i c a t i o n i s t h e n a t u r e o f t h e process by
w h i c h polymer molecules may be b u i l t up and t h i s aspect
i n more d e t a i l
1.3
Is discussed
below.
POLYMER GROWTH MECHANISMS
a)
Chain-Growth P o l y m e r i z a t i o n
T h i s t y p e o f r e a c t i o n proceeds v i a t h e f o l l o w i n g s t e p s ;
i n i t i a t i o n , p r o p a g a t i o n and t e r m i n a t i o n , each i n v o l v i n g a
d i f f e r e n t mechanism and r a t e o f r e a c t i o n .
u s u a l l y f a s t e r than t h a t o f a t y p i c a l
The o v e r a l l
step-growth polymerization
and t h e p r o d u c t tends t o have a h i g h m o l e c u l a r w e i g h t .
e s s e n t i a l f e a t u r e o f t h i s t y p e o f process
m o l e c u l a r w e i g h t p r o d u c t s can be formed
The
i s t h a t monomer u n i t s
r e a c t o n l y w i t h t h e r e a c t i v e c h a i n ends and c o n s e q u e n t l y
monomer.
rate i s
high
i n t h e presence o f
b)
Step-Growth P o l y m e r i z a t i o n
In t h i s case t h e polymer c h a i n grows a t a r e l a t i v e l y slow
r a t e o v e r a much l o n g e r p e r i o d o f t i m e compared w i t h c h a i n - g r o w t h
polymerization.
i n s t e p - g r o w t h p o l y m e r i z a t i o n t h e f u n c t i o n a l group o f t h e
monomer has t h e same r e a c t i v i t y as t h e f u n c t i o n a l group on t h e
end
o f a growing polymer c h a i n ,
c o n s e q u e n t l y monomer u n i t s can
r e a c t w i t h o t h e r monomer u n i t s o r polymer c h a i n s w i t h equal
ease.
T a b l e 1-1"* l i s t s t h e i m p o r t a n t d i f f e r e n c e s
between t h e
two growth processes.
TABLE 1-1
C h a r a c t e r i s t i c s o f t h e L i m i t i n g Types o f P o l y m e r i z a t i o n Reactions
Characteristic
Step-Growth P o l y m e r i z a t i o n
Chain-Growth P o l y m e r i z a t i o n
Component
Reactions
I n i t i a t i o n , p r o p a g a t i o n and
termination
reactions
essentially identical in
r a t e and mechanism.
I n i t i a t i o n , p r o p a g a t i o n and
termination
reactions
significantly different in
r a t e and mechanism.
Polymer
Growth
Slow, random g r o w t h o f
polymer w i t h h i g h
reaction conversion
required f o r a high
degree o f p o l y m e r i z a t i o n .
Rapid, p r e f e r e n t i a l growth
o f each polymer c h a i n ,
once i n i t i a t e d , w i t h h i g h
degrees o f p o l y m e r i z a t i o n
attained at the start of
the r e a c t i o n .
Reactivity
of
Monomer
Monomer c a p a b l e o f
combining w i t h i t s e l f
o r w i t h any o t h e r s p e c i e s
present w i t h equal
facility, resulting in
rapid disappearance o f
monomer a t e a r l y stages
of t h e polymerization
reaction.
Monomer c a p a b l e o f
r e a c t i n g o n l y w i t h an
a c t i v e end-group on a
polymer c h a i n , r e s u l t i n g
in s t e a d i l y decreasing
but s i g n i f i c a n t conc e n t r a t i o n s o f monomer
throughout t h e polymerization reaction.
C a r o t h e r s showed t h a t t h e a t t a i n a b l e D.P.
f o r a step-growth
p o l y m e r i z a t i o n c o u l d be r e l a t e d t o t h e r e a c t i o n c o n v e r s i o n by the
simple expression -
- where p i s t h e f r a c t i o n a l c o n v e r s i o n .
t h i s expression
The
I s t h a t h i g h D.P.'s f o r s t e p - g r o w t h processes can o n l y
be achieved a t very h i g h r e a c t i o n c o n v e r s i o n s .
illustrated
i n t h e F i g . 1.1
Applying Carothers
This point i s
, i n which i t i s e v i d e n t t h a t t h e random
growth o f t h e polymer p e r m i t s o n l y a g r a d u a l
size.
Implication of
1
increase i n molecular
e q u a t i o n , assuming no s i d e r e a c t i o n s
o c c u r i t i s easy t o show t h a t a D.P.
o f 16 r e q u i r e s a c o n v e r s i o n o f
93.75% and a "DTP. o f 50 r e q u i r e s 98% c o n v e r s i o n .
M.
i>
M
M
M
M
l
M,
M,
M
M
M,
M.
l
M
M
l
ft,
l
M,
25%
reacted,
D.P.
50%
reacted,
D.P.
75%
reacted,
D.P.
.—Mi
M
M,
M
M,
*2
M,
M
\
M
l
l
"2
M ^ M,
M
M
l
M.
l
Mi.
l
M:
M,
-> M.
M,
M,
M,
=
5
=
8
M,
\
M
3
>M
" 13
*8
M
3
87.5%
r e a c t e d , D.P.
1.4
PHOTOPOLYMERIZATION
Before t h e t u r n o f t h e c e n t u r y B l y t h e and Hoffman made a polymer
by
I r r a d i a t i n g styrene**.
The whole process I s I n i t i a t e d by U.V.
light,
which i n t e r a c t s w i t h t h e monomer t o produce r a d i c a l s ; p r o p a g a t i o n o f
t h e c h a i n by a d d i t i o n o f monomer t o r a d i c a l c h a i n ends f o l l o w s .
Other compounds besides
t h e monomer, may be used as i n i t i a t o r s , f o r
example o r g a n i c s u l p h u r compounds, azo compounds, metal
and peroxides**.
carbonyls
The quantum y i e l d s f o r t h e above t y p e o f photo-
3
p o l y m e r i z a t i o n s can be o f t h e o r d e r o f 10
point
o r more.
i s t h a t t h e l i g h t used c r e a t e s t h e I n i t i a t o r
The i m p o r t a n t
i n t h i s type o f
p h o t o p o l y m e r i z a t i o n , which then proceeds by a c h a i n growth
Another i m p o r t a n t photochemical
t h e cross-1 i n k i n g o f polymers.
importance
process.
process t h a t may t a k e p l a c e i s
The work o f Minsk'' was o f prime
i n t h e development o f t h i s f i e l d , w i t h h i s p r e p a r a t i o n o f
p o l y ( v i n y l cinnamate) and t h e use o f dyes as a means o f photos e n s i t i z i n g t h e cross-1 i n k i n g process.
Examples o f l i g h t
sensitive
u n i t s which may be i n c o r p o r a t e d i n t o polymers a r e o l e f i n s , a z i d e s
and d i a z c n i u m s a l t s .
The
two processes d e s c r i b e d above have commonly been
referred
t o as p h o t o p o l y m e r i z a t i o n s , both processes have been t h e s u b j e c t o f
i n t e n s i v e research and commercial e x p l o i t a t i o n , p a r t i c u l a r l y i n t h e
s u r f a c e c o a t i n g s , p r i n t i n g and e l e c t r o n i c
industries.
More r e c e n t l y examples have been p u b l i s h e d o f p o l y m e r i z a t i o n s
i n w h i c h each new bond i n t h e polymer backbone i s formed as t h e
r e s u l t o f a photochemical
Oe Schryver
process and t h i s has l e d Smets and
t o suggest t h a t t h e term p h o t o p o l y m e r I z a t i o n s h o u l d be
r e d e f i n e d as a s t e p - g r o w t h
p o l y m e r i z a t i o n I n w h i c h each p r o p a g a t i n g
g
s t e p r e q u i r e s t h e a b s o r p t i o n o f a quantum o f l i g h t
.
They go
f u r t h e r and propose t h r e e c l a s s e s w i t h i n t h i s r e d e f i n e d s u b j e c t ,
depending on t h e species
species may
Involved in the propagation step.
This
be a r e a c t i v e ground s t a t e f o l l o w i n g a photochemical
react!
a singlet excited state or a t r i p l e t excited state.
The
p u b l i s h e d examples o f p h o t o p o l y m e r i z a t i o n as r e d e f i n e d
above, have i n v o l v e d i r r a d i a t i o n o f n o n - c o n j u g a t e d b i c h r o m o p h o r i c
q
monomers (see l a t e r )
t h e design o f new
.
p h o t o p o l y m e r i z a t i o n s i t I s not s u f f i c i e n t t o s i m p l y
p l a n a s y n t h e s i s o f a new
will
However, i t i s w o r t h p o i n t i n g o u t t h a t i n
non-conjugated b i c h r o m o p h o r i c system which
then be i r r a d i a t e d , s i n c e a number o f processes o t h e r than
p h o t o p o l y m e r i z a t i o n can o c c u r ,
these are i l l u s t r a t e d
g
i n F i g u r e 1.2 .
FIGURE 1.2
Possible
reaction pathways i n n o n - c o n j u g a t e d
)
(ZD
bichromophores
H
8
Key
) • chromophoric g r o u p ;
* • p h o t o e x c i t e d group.
7.
The
a)
possible
r e a c t i o n pathways i n d i c a t e d i n F i g u r e 1.2 a r e ; -
d e a c t i v a t i o n o f t h e e x c i t e d s t a t e r e t u r n i n g t h e monomer
t o t h e ground s t a t e ,
b)
d e l o c a l i z a t i o n o f t h e e x c i t e d s t a t e over t h e two
chromophores,
c)
d e a c t i v a t i o n o f t h e p r o d u c t r e s u l t i n g f r o m b) t o g i v e
starting material,
d)
and
e)
f o r m a t i o n o f cyclomer,
f)
and
g)
Intramolecular
energy t r a n s f e r (when
chromophores a r e n o t I d e n t i c a l ) ,
h)
d e a c t i v a t i o n o f t h e complex a r i s i n g f r o m
Intramolecular
energy t r a n s f e r ,
i)
All
t h e above processes a r e an a l t e r n a t i v e t o t h i s
path,
which r e p r e s e n t s p h o t o p o l y m e r i z a t l o n .
1.5
SOME EXAMPLES OF STEP-GROWTH PHOTOPOLYMERIZATION
a)
Photopolymerlzatlon v i a the S i n g l e t
State
When i r r a d i a t e d , anthracene undergoes p h o t o d i m e r i z a t i o n
a t the 9, 10 p o s i t i o n s , and a t t h e same t i m e i t looses i t s
a r o m a t i c i t y and p l a n a r i t y , due i n p a r t t o e l e c t r o s t a t i c
repulsion'**
(1.1).
O
MO O O
O
1.0
hv
o
o
8.
Extending
t h e use o f t h i s r e a c t i o n t o t h e p o l y m e r t z a t i o n o f
b i s a n t h r a c e n e has produced s e v e r a l polymers o f t h e g e n e r a l
structure
H
i n d i c a t e d I n F i g u r e 1 . 3 (1.2)
0
hv
Polymers have been made where R = -CH.-O-C- (CH_) -C-0-CH-2
||
2'n ||
2
0
0
and
R = -C-0- (CH,) -0-C2
II
0
n
II
0
An I m p o r t a n t p o i n t t o note i n r e l a t i o n t o these r e s u l t s i s t h a t
t h e polymers d e r i v e d from b l s a n t h r a c e n e s w i t h R = -CH_-0-C- (CH„) -C-0-CH-II
II
0
0
2
were I n v a r i a b l y o f s i g n i f i c a n t l y
lower m o l e c u l a r w e i g h t
f r o m monomers where R = -C-0-(CH„) -0-C-.
II
II
0
0
2
the potential
2
n
2
than those d e r i v e d
This observation
illustrates
n
importance o f p o s s i b l e s i d e r e a c t i o n s s i n c e i n t h e former
case a 1,5 - s i g m a t r o p i c hydrogen s h i f t
( f r o m t h e methylene a t C-9 t o t h e
C-10 p o s i t i o n ) can a c t as a c h a i n t e r m i n a t i n g c o m p e t i t o r t o t h e c h a i n
p r o p a g a t i n g anthracene d i m e r l z a t i o n .
The r e s u l t
p a r t i c u l a r Importance o f a d e t a i l e d u n d e r s t a n d i n g
in designing a photopolymerization.
illustrates the
o f t h e model r e a c t i o n
9.
b)
Photopolymerlzatlon v i a the T r i p l e t
State
Coumarins may be d i m e r f z e d v i a a benzophenone s e n s i t i z e d
12
r e a c t i o n as i n d i c a t e d below
(1.3)
0
I
hv
Ph.CO
Me
Me-C-0
O-C-Me
O
O
(1.3)
( 9 5 % head-to-head
exo).
By analogy,
e q u a t i o n (1 M)
R'
b i s c o u m a r i n s have y i e l d e d polymers a c c o r d i n g t o
13
.
R'
(i.^)
Another example o f t h i s t y p e o f r e a c t ton i s t h e 2 + 2
photc-
c y c l o a d d i t i o n o f t e t r a c h l o r o b i s t n a l e l m i d e s (sheme 1.5; r o u t e b; R=CI).
o
n
R
R
/
M O O
N
2'n
R
R
a
R
/
(OH.)
0
Insoluble cross
l i n k e d polymer
R
(CH.) -N
2'u
t
R
(cm)
N
//
J
-N
T
o
In t h e l a t t e r example, t h e a u t h o r s emphasised t h e c r i t i c a l
importance o f monomer p u r i t y t o s u c c e s s f u l p o l y m e r i z a t i o n .
p r a c t i c e , two samples o f monomer p u r i f i e d by d i f f e r e n t
were a p p a r e n t l y
identical
inall
a genuine polymer on i r r a d i a t i o n
In
techniques
r e s p e c t s except t h a t one y i e l d e d
i n t h e presence o f benzophenone as
t r i p l e t s e n s i t i z e r whereas t h e o t h e r was recovered
as unchanged
monomer a f t e r t h e same t r e a t m e n t , t h e d i f f e r e n c e i n b e h a v i o u r
being
a t t r i b u t a b l e t o a low c o n c e n t r a t i o n o f an u n i d e n t i f i e d b u t e f f e c t i v e
triplet
quencher.
11.
c)
P h o t o p o l y m e r I z a t I o n v i a a R e a c t i v e I n t e r m e d i a t e Formed
i n an
Initial
Photochemical Process
When b i s - m a l e i m l d e s are i r r a d i a t e d
benzene o r an a l k y l benzene l i n e a r polymers
process.
i n t h e presence
are formed
of
i n a two
stage
I n t h e f i r s t s t a g e a maleimide u n i t adds p h o t o c h e m i c a l l y
to the aromatic r i n g
(1.6).
R
hv,
In t h e second stage t h i s I n i t i a l
Xn
(1.6)
p r o d u c t r e a c t s v i a a ground
s t a t e Diels-Alder C y c l o a d d i t i o n reaction t o give the f i n a l
« - 0
polymer
(1.7).
P
(1.7)
Another example o f t h i s t y p e o f p h o t o p o l y m e r i z a t i o n i s t h e
p h o t o r e d u c t l v e p o l y m e r i z a t i o n o f b i s a r o m a t i c ketones.
The
photo-
\h 15
r e d u c t i o n o f benzophenone t o benzopinacol
i s a w e l l known r e a c t i o n
and a t t e m p t s t o e x t e n d i t t o t h e f o r m a t i o n o f p o l y b e n z o p i n a c o l s
have been d e s c r i b e d by s e v e r a l groups o f workers
OH
0
0
n
ii
ArCAr'CAr
This r e a c t i o n w i l l
hv
isopropanol/'
coBolvent
I
I
'
(1.8)
OH
I
(1.8)
C-Ar'— C
L
Ar
be d i s c u s s e d I n g r e a t e r d e t a i l
LJ
n
i n the next
c h a p t e r , s i n c e a t t e m p t s t o u t i l i z e and extend i t s a p p l i c a b i l i t y f o r m a
s u b s t a n t i a l p a r t o f t h e work r e p o r t e d i n t h i s
thesis.
,
CHAPTER 2
PHOTOREDUCTIVE POLYMERIZATION
2.1
PHOTOCHEMICAL PROCESSES
In most o r g a n i c molecules
t h e a b s o r p t i o n o f a quantum I n t h e
u l t r a v i o l e t / v i s i b l e r e g i o n o f t h e spectrum
s t a t e , which
i s s l i g h t l y h i g h e r i n energy
molecule;
excited
than t h e t r i p l e t o f t h e same
F i g 2.1 shows t h e major p o s s i b l e s t a t e s f o r
electronic configuration.
the
leads t o a s i n g l e t
t h e i r r e l a t i v e e n e r g i e s and t h e pathway between them as
21
d e p i c t e d i n schematic f o r m by J a b l o n s k i
r a d i a t i o n o r photochemical
may
.
Before any e m i s s i o n o f
r e a c t i o n , t h e two r a d i a t i o n l e s s
processes
occur:
i)
I n t e r n a l Conversion
degenerate
i s a r a d l a t i o n l e s s t r a n s i t i o n between
s t a t e s o f t h e same m u l t i p l i c i t y .
Such t r a n s i t i o n s
are e x t r e m e l y r a p i d , hence t h e n e g l i g i b l e e m i s s i o n f r o m upper
states.
I n t e r n a l c o n v e r s i o n from t h e f i r s t e x c i t e d
singlet
s t a t e ( S p * S ) i s so much slower, t h a t f l u o r e s c e n c e can compete.
Q
ii)
Intersystem Crossing
i s a r a d i a t i o n l e s s t r a n s i t i o n between
states o f d i f f e r e n t m u l t i p l i c i t y .
t r i p l e t by t h i s r o u t e i s a process
phosphorescence.
D e a c t i v a t i o n o f t h e lowest
in competition with
normal
The i n t e r s y s t e m c r o s s i n g (S^-»T^ o r Sp>T )
n
is c o m p e t i t i v e w i t h f l u o r e s c e n c e and i s t h e process by w h i c h
the
t r i p l e t manifolds are normally populated.
T|—»S| i s e n d o t h e r m i c .
The t r a n s i t i o n
R a d i a t i v e t r a n s i t i o n s on t h e o t h e r hand
i n v o l v e an e x c i t e d s p e c i e s passing f r o m a h i g h e r e x c i t e d
t o a lower one w i t h e m i s s i o n o f a photon.
d e s c r i b e d below can occur:
The t h r e e
state
processes
The J a b l o n s k i Diagram
F i g u r e 2.1
iil)
F l u o r e s c e n c e r e s u l t s from a r a d i a t i v e t r a n s i t i o n between
s t a t e s o f t h e same m u l t i p l i c i t y and i s a r a p i d
(K^ ~ 10^- 10^5 ^) •
For p o l y a t o m i c molecules
organic chemistry the t r a n s i t i o n is u s u a l l y
5v
of
process
encountered i n
S^—>SQ,
Phosphorescence i s t h e r e s u l t o f a t r a n s i t i o n between s t a t e s
d i f f e r e n t m u l t i p l i c i t y t y p i c a l l y T^->SQJ T —>SQ i s v e r y r a r e .
n
The process, being s p i n f o r b i d d e n , has a much s m a l l e r r a t e c o n s t a n t
-2
(K~10
P
v)
k -1
-10 S ) than t h a t f o r f l u o r e s c e n c e .
Delayed f l u o r e s c e n c e d i f f e r s f r o m o r d i n a r y f l u o r e s c e n c e i n
t h a t t h e measured r a t e o f decay o f emission
i s l e s s than t h a t
expected f r o m t h e t r a n s i t i o n g i v i n g r i s e t o t h e e m i s s i o n .
process
via
The
i s u s u a l l y observed when e x c i t e d s i n g l e t s a r e p o p u l a t e d
endothermlc i n t e r s y s t e m c r o s s i n g f r o m t h e c o r r e s p o n d i n g
t r i p l e t s , or via t r i p l e t - t r i p l e t
annihilation.
1*4.
2.2
THE CARBONYL CHROMOPHOBE
Compounds c o n t a i n i n g t h e c a r b o n y l chromophore a r e among t h e most
thoroughly i n v e s t i g a t e d in photochemistry.
A l i p h a t i c ketones and
aldehydes show a weak a b s o r p t i o n band around 280 - 300 n.m. a r i s i n g
from t h e f o r b i d d e n n , 7T t r a n s i t i o n .
t h e vacuum u l t r a v i o l e t r e g i o n a t 195,
transitions.
s t a t e i s mainly
compounds.
Strong a b s o r p t i o n occurs i n
170 and 155 n.m. a s s o c i a t e d w i t h
The lowest t r i p l e t
i s an T\ ,
s t a t e and
this
r e s p o n s i b l e f o r t h e observed p h o t o c h e m i s t r y o f c a r b o n y l
Exceptions
t o t h i s g e n e r a l i s a t i o n can o c c u r where t h e
c a r b o n y l group i s c o n j u g a t e d ;
and 7T, 71* s t a t e s are lowered
i n such compounds b o t h t h e n ,7T"
i n energy.
The d e t a i l e d e f f e c t depends
on t h e s t r u c t u r e o f t h e p a r t i c u l a r compound and
the p o l a r i t y o f the
s o l v e n t used.
can become t h e
In some cases theTT, 7T
energy e x c i t e d s t a t e and
triplet
i n such cases t h e photochemical
lowest
behaviour i s
not t h a t t y p i c a l l y a s s o c i a t e d w i t h c a r b o n y l compounds.
Upon e x c i t a t i o n o f t h e c a r b o n y l chromphore an e l e c t r o n i s
t r a n s f e r r e d f r o m a non-bonding o r b i t a l
l o c a l i z e d m a i n l y o n t h e oxygen
atom t o an a n t i - b o n d i n g 7T o r b i t a l w h i c h I s a s s o c i a t e d w i t h b o t h
carbon and oxygen n u c l e i .
As a consequence o f t h i s r e d i s t r i b u t i o n o f
e l e c t r o n d e n s i t y , n u c l e o p h i 1 «'t
t y p i f i e s carbonyl chemistry,
the
a t t a c k a t t h e carbon atom w h i c h
i s no l o n g e r I m p o r t a n t ; t h e e l e c t r o n i c
f e a t u r e o f t h e e x c i t e d species o f g r e a t e s t s i g n i f i c a n c e i s i t s
resemblance t o an a l k o x y r a d i c a l , and indeed
I t s chemical
is c l o s e l y a l l i e d t o t h a t o f a l k o x y r a d i c a l s .
reactivity
The major r e a c t i o n s o f
e x c i t e d c a r b o n y l compounds a r e c l e a v a g e o f t h e C-C bond t * t o t h e
carbonyl
( N o r r i s h Type 1 ) , hydrogen a b s t r a c t i o n r e a c t i o n s ( N o r r i s h
Type 11) and a d d i t i o n r e a c t i o n s t o o l e f i n s which f i n d t h e i r
i n t h e w e l l known r e a c t i o n s o f a l k o x y r a d i c a l s
(2.1 - 2 . 3 ) .
parallels
15.
\
\
cf. R - C - O /
R
/
\
R-C=0
(
/
c=o
<n.r.N
r H
C=0
R
\.
-»
C-OH
/
/
(n.n*)
R
+ R'
R
+R'
R
\
R
\
N
Y
w
(2.2)
cf. R - C - O - -+ R - C - O H
/
/
R
R
+ 'R'
/C
Vo^R 3(
*
R
+ R-
R
(2.1)
C=0
cf.
N o r r i s h Type 1 cleavage may occur
I-C-O-5R
R
Vo
(2.3)
via e i t h e r the excited t r i p l e t
o r s i n g l e t s t a t e and i t s e x t e n t i s dependent on s u b s t i t u t i o n a t t h e
carbon.
T h i s process i s u n i m p o r t a n t when c o n s i d e r i n g s o l u t i o n phase
p h o t o c h e m i s t r y o f d i a r y l ketonessuch as benzophenone, when an u n s t a b l e
phenyl
r a d i c a l would be produced.
N o r r i s h Type 11 processes o c c u r w i t h c a r b o n y l compounds
possessing
^ h y d r o g e n s w h i c h may be a b s t r a c t a b l e by t h e c a r b o n y l group upon TV ,TT
excitation
(2 .k) .
H
0 \ ^
H
2.3
R
f CH
L
?
||
2
PHOTOREDUCTION OF CARBONYL COMPOUNDS
The p h o t o r e d u c t i o n o f c a r b o n y l compounds i n s u i t a b l e hydrogen
22
d o n a t i n g s o l v e n t s has been i n v e s t i g a t e d s i n c e t h e t u r n o f t h e c e n t u r y
23
The e a r l y work o f C i a m i c i a n and S i l v e r
I n d i c a t e d t h a t benzophenone
16.
was reduced t o benzopinacol on exposure o f an a l c o h o l i c s o l u t i o n o f t h e
ketone t o s u n l i g h t
(2.5).
0
OH OH
.
.
U
TuSfcf (®f-(®)
2
In t h e presence o f a l k a l i
2
i t was found t h a t benzhydrol
2
was formed **.
Bachmann showed t h a t i n t h e presence o f a s o d i u m - 2 - p r o p a n o l a t e a s e r i e s
o f p h o t o r e d u c t i o n s o f benzophenone and s u b s t i t u t e d benzophenones i n
i s o p r o p a n o l gave benzhydrols
f o r m a t i o n o f benzhydrol
i n high y i e l d s .
The mechanism f o r t h e
f r o m benzophenone I n t h e presence o f a l k a l i
2k 25
Is a m a t t e r i n d i s p u t e ' .
The most i n t e n s i v e l y s t u d i e d r e a c t i o n i s t h e a c t u a l p h o t o r e d u c t i v e
coupling yielding
1,2-ethanediols.
Aldehydes and ketones b o t h undergo
22
the r e a c t i o n
, ketones having r e c e i v e d by f a r t h e most a t t e n t i o n .
Benzophenone
I s t h e most t h o r o u g h l y s t u d i e d ketone,
benzopinacol
i n quantative y i e l d .
yielding
The quantum y i e l d f o r t h e f o r m a t i o n
o f acetone i n t h e p h o t o r e d u c t i o n o f benzophenone i n i s o p r o p a n o l i s
n e a r l y constant using i r r a d i a t i o n a t several d i f f e r e n t wavelengths
between 366 and 25^ n.m. s u g g e s t i n g t h a t b o t h TV , 7 V * e x c i t a t i o n and
$
26 27
7T, 7T e x c i t a t i o n may b r i n g about t h e r e a c t i o n ' .
Various solvents
have been used as hydrogen donors,
i n p a r t i c u l a r a l c o h o l s and a l k y l -
28 29
benzenes
'
.
Many comparisons o f s o l v e n t s have been made w i t h
benzophenone as r e a c t i n g ketone.
disappearance
Some quantum y i e l d s o f benzophenone
i n v a r i o u s s o l v e n t s a r e t a b u l a t e d below (Table 2 . 1 ) ^ .
17-
MOLAR CONCENTRATION
BENZOPHENONE
SOLVENT
OF
QUANTUM YIELD OF
DISAPPEARANCE
0.002
10"**
Water
ID"
2
0.05
Toluene
10"
2
0.45
Hexane
I O - W
Benzene
1.0
1
Ethanol
icf*-10"
Isopropanol
10~ - 10"
5
1.0
1
0.8
to 2.0
I f t h e bond e n e r g i e s f o r hydrogen a b s t r a c t i o n a r e h i g h enough
( > 100 K c a l mole ') t o p r e v e n t hydrogen a b s t r a c t i o n by t h e t r i p l e t
29
w i t h a n y t h i n g o t h e r than v e r y
low c o l l l s i o n a l
y i e l d s o f benzophenone d i s a p p e a r a n c e w i l l
efficiency
tend t o z e r o .
, t h e quantum
For hexane,
t o l u e n e and e t h a n o l , quantum y i e l d s a r e l e s s than o r equal
Independent o f
concentration-
t o u n i t y and
and i t I s suggested t h a t a l l
benzophenone t r i p l e t s a b s t r a c t a hydrogen atom, t h e a p p r o p r i a t e C-H
bond e n e r g i e s
i n hexane and t o l u e n e b e i n g a p p r o x i m a t e l y 85 and 80
Kcalmole"' respectively.
r e a c t i o n s o f t h e r a d i c a l R*
The t h e r m a l
formed on a b s t r a c t i o n f r o m t h e s o l v e n t RH w i l l
quantum y i e l d .
affect the overall
The r e v e r s a l o f t h e a b s t r a c t i o n r e a c t i o n can r e s u l t i n
and o v e r a l l quantum y i e l d o f l e s s t h a n u n i t y
Ph C0H + R"
»
2
Whereas quantum y i e l d s
(2.6).
Ph C0 + RH
(2.6)
2
i n isopropanol
tend t o a l i m i t i n g
value
of
2 , since the solvent radical
to
a ground s t a t e benzophenone w i t h t h e p r o d u c t i o n o f acetone and a
diphenyl
ketyl
radical
(2.7).
( C H ) C 0 H + Ph C0
3
2
( ( C H ^ ^ C O H ) may t r a n s f e r a hydrogen
2
> ( C H ) C 0 + Ph C0H
3
2
Such t r a n s f e r r e a c t i o n s a r e e n e r g e t i c a l l y
(2.7)
2
improbable
i n t h e benzyl
18.
o r h e x y l r a d i c a l s d e r i v e d from t o l u e n e o r hexane.
d e r i v e d f r o m t h e k e t y l and s o l v e n t r a d i c a l s was
The
In-cage dimer,
d e t e c t e d In e a r l y
i n v e s t i g a t i o n s of photoreduction i n toluene, but f a i l u r e t o detect the
in-cage dimer f o r p h o t o r e d u c t l o n s i n Isopropanol
d i s p u t e and d i s c u s s i o n o f t h e mechanism o f t h i s
The
led t o considerable
process.
s t r u c t u r e o f the p o s s i b l e i n t e r m e d i a t e s I n v o l v e d has been t h e
s u b j e c t o f much c o n t r o v e r s y ; f o r example F l l i p e s c u has proposed t h a t
t h e y e l l o w c o l o u r f r e q u e n t l y observed d u r i n g i r r a d i a t i o n o f s o l u t i o n s
of aromatic
ketones I s caused by an I n t e r m e d i a t e o f s t r u c t u r e ( I )
in
t h e case o f benzophenone and * t - a l k y l s u b s t i t u t e d benzophenones.
He suggested t h e r e a c t i o n scheme ( 2 . 8 ) .
P^COCTj) + (CH ) CH0H
^PhjpOH + (CH^COH
Ph C0H +
> (I)
3
2
fcH ) C0H
2
3
2
(R=H)
(2.8)
I + Ph C0
> 2Ph COH + (CH ) CO
2Ph C0H
>
2
2
2
I t was
reaction
Ph C(0H)C(0H) Ph
2
2
2
proposed t h a t (X) y i e l d e d p r o d u c t s v i a a ground s t a t e
(2.9).
QH
|
F
3
h
'
C
CH
, ,X
3
T\;
W
X
CH
/ 3
X^^H^-^O^C^
R
^Ph
'
*
2
Products
31
Recent work by Weiner
appears t o have e s t a b l i s h e d the mechanism
o f p h o t o r e d u c t i o n o f benzophenone i n i s o p r o p a n o l beyond reasonable
and he a l s o i s o l a t e d t h e e l u s i v e In-cage dimer.
summarized i n scheme ( 2 . 1 0 ) .
The mechanism i s
9
<'>
doubt
19.
Ph CO(T,) + (CH ) CHOH
2
Spin f l i p ,
3
*
2
Ph COH
(CH ) COH
2
3
2
(c)
Ph C(0H)C(0H) ( C H )
In-cage c o m b i n a t i o n (c)
2
In cage H - t r a n s f e r ( c )
3
2
» Ph CH0H + (Ch\,) C0
9
o
(2.10)
m i g r a t i o n o u t o f cage (c)
*
H - t r a n s f e r (CH^COH + Ph C0
Ph C0H + (CH-).COH
o
> (CH,) C0 + Ph_C0H
2
o
OH
d i m e r i z a t i o n : 2Ph.C0H
>
Ph
2
OH
- C - C - Ph
2
The s i g n i f i c a n t p r o p o r t i o n o f cage r e a c t i o n
(11%) r e q u i r e s
that
i n t h e p a i r o f r a d i c a l s c o m p r i s i n g (C) (where t h e e l e c t r o n s p i n s a r e
i n i t i a l l y p a r a l l e l ) , s p i n f l i p p i n g must o c c u r I n some r a d i c a l
p r i o r t o d i f f u s i o n out o f the solvent
pairs
cage.
The m a j o r i t y o f p h o t o r e d u c t i v e processes w i t h quantum y i e l d s
approaching u n i t y o c c u r when t h e n, TV
excited state.
triplet
i s t h e lowest
The e f f e c t i v e n e s s o f t h e r e a c t i o n has been a t t r i b u t e d
t o t h e h i g h l y l o c a l i s e d n e l e c t r o n on t h e oxygen.
7T, 7T
triplet
i n cases where t h e
i s t h e lowest e x c i t e d s t a t e t h e u n p a i r e d e l e c t r o n s a r e
more d e l o c a l i z e d and hydrogen a b s t r a c t i o n
and
lying
relatively
inefficient
3 2 , 3 3
A t h i r d type o f possible
transfer state
.
i susually
endothermic
.
lowest l y i n g t r i p l e t
s t a t e I s a charge-
Such s t a t e s have been e x t e n s i v e l y
i n v e s t i g a t e d and
occur i n a r o m a t i c ketones where an e l e c t r o n donor s u b s t i t u e n t
as h y d r o x y l ,
(such
amino, methoxy, e t c . ) i s s i t u a t e d para w i t h r e s p e c t t o
t h e c a r b o n y l group.
2.k
PHOTOREDUCTIVE POLYMERIZATION
The photochemical r e d u c t i v e c o u p l i n g
utilised
i n polymer s y n t h e s i s
Ph-HC=N-(- CH ) -N=CH-Ph
2
x
o f a b i s i m l n e has been
(2.11).
4
alcohol
(sensitizer)
-6-CH-NH -f-CH ) -NH-CH - ) —
I
/ x
i
n
0
Ph
Ph
(2.10
20.
However, c o n s i d e r a b l y more work has been r e p o r t e d on t h e photor e d u c t i v e c o u p l i n g o f a r o m a t i c d i k e t o n e s , and t h i s work I s d i r e c t l y
r e l e v a n t t o t h e main o b j e c t i v e s o f t h e work r e p o r t e d here.
The
process can be summarized as shown below, blsbenzophenone b e i n g
photoreduced
t o a polybenzopinacol (2.12).
OH
I
PhCOCgH. - X- C H. C0C H
6
6
_hv
H donor
5
OH
I
C
X
C
'f " f " 6 V ~ 6 V
Ph
(2.12)
Ph
The idea i s s i m p l e and i t i s n o t t o o s u r p r i s i n g t o f i n d t h a t two
of
the f i r s t
papers on t h e s u b j e c t o f s t e p - g r o w t h p h o t o p o l y m e r i z a t i o n
d e s c r i b e d a t t e m p t s t o r e a l i s e t h e s y n t h e s i s I n d i c a t e d above.
2 .4
a) E a r l y r e s u l t s on p h o t o r e d u c t i v e p o l y m e r i z a t i o n s o f d i k e t o n e s
The f i r s t b e i n g by H i g g i n s e t a l ' ^ who o b t a i n e d low m o l e c u l a r
weight p o l y b e n z o p i n a c o l s on i r r a d i a t i o n o f benzene-isopropanol
s o l u t i o n s o f a r o m a t i c d i k e t o n e s (JLa—c),
their results are
summarized below (2.13) and i n T a b l e 2.2.
0
0
II
H
C H C-Ar-C-C H
6
5
6
5
OH
OH
I
I
(2.13)
0 Ar-C
-jj-
1
n
C
I
H
C
6 5
H
6 5/^v
nr
a, Ar =
b, Ar =
--©-
c, Ar =
Polymer P r o p e r t i e s
Polymer
Viscosity
M.Pt.
M
TTTa
0.12
140
825
rJ 3
mb
0.06
135
435
~ IS
UJc
0.14
160
805
^ 2
T a b l e 2.2
D.P.
21
From t h e data
( t a b l e 2.2) I t
t r l m e r s were o b t a i n e d .
Is e v i d e n t t h a t o n l y dimers and
The I n f r a r e d s p e c t r a o f t h e p r o d u c t s
showed a small peak remaining a t 1650 cm"' I n d i c a t i n g u n r e a c t e d
c a r b o n y l groups were p r e s e n t .
The a u t h o r s suggested p o s s i b l e e x p l a n a t i o n s f o r t h e above
observations.
The low D.P.'s o b t a i n e d were a t t r i b u t e d t o
complete r e d u c t i o n o f t h e c a r b o n y l f u n c t i o n t o a benzhydrol
c h a i n end, as I l l u s t r a t e d
i n s t r u c t u r e 2.14.
II
H
Ar
C^H.-C-Ar-C
The r e s i d u a l
OH
OH
OH
like
id
C^H
C,H
c a r b o n y l f u n c t i o n was accounted f o r I n terms o f c h a i n ends ( s e e
2.1)
and u n r e a c t e d monomer.
However, t h e e x p l a n a t i o n o f low
D.P.'s i n terms o f benzhydrol
valid
l i k e u n i t s seems u n l i k e l y t o be
I n view o f r e s u l t s o b t a i n e d subsequently
by o t h e r w o r k e r s
(see l a t e r ) .
They concluded
by s t a t i n g t h a t t h e r e a c t i v i t i e s
of the radical
intermediates involved i n t h i s attempted
m e r i z a t i o n appeared t o be d i f f e r e n t t o those
poly-
i n v o l v e d i n t h e model
r e a c t i o n , namely benzophenone p h o t o r e d u c t i o n .
At about t h e same t i m e Pearson and T h i e m a n n ^ worked on j u s t
one o f t h e monomers i n v e s t i g a t e d by H i g g l n s .
They
irradiated
p-dibenzoylbenzene i n an Isopropanol-benzene m i x t u r e and o b t a i n e d
a product w i t h a m o l e c u l a r w e i g h t o f 1570 whereas H i g g i n s had
r e p o r t e d a v a l u e o f ^35.
these two e x p e r i m e n t s ,
The s o l v e n t c o m p o s i t i o n s
on a volume b a s i s H l g g l n s
1
differed f o r
work used a 1 : 1
benzene : i s o p r o p a n o l m i x t u r e whereas Pearson's work used a 3 : 1
r a t i o ; t h e importance
again l a t e r .
shown i n scheme
o f solvent composition w i l l
be r e f e r r e d t o
Pearson and Thiemann proposed t h e r e a c t i o n sequence
.15).
22.
OH
C,H.-C=
C-C/H
OH
(2.1
OH
I
C
H
6 S °6 5
H
C
Where X, t h e c a p p i n g group i s p a r t l y
and
H
6 5
(CH^-COH, p a r t l y H
p a r t l y where t h e ends o f t h e polymer a r e e y e U s e d a t t h e X
positions.
They a l s o a t t r i b u t e d
the yellow colouration typical
o f these r e a c t i o n s t o t h e s t r u c t u r e T J T „ because o f t h e long wavel e n g t h a b s o r p t i o n and t h e r e l a t i v e s t a b i l i t y o f t h e I n t e r m e d i a t e ,
though i t i s observed t o decay w i t h t i m e .
A l t h o u g h as t h e a u t h o r s
point o u t , t h e y e l l o w c o l o u r a t i o n I s also observed f o r t h e
m=dibenzoyl benzene case where such a s t r u c t u r e i s n o t p o s s i b l e .
These e a r l y a t t e m p t s were n o t v e r y s u c c e s s f u l ; degrees o f
polymerization o f h t o 5 being obtained.
The m a j o r reasons why
they were n o t s u c c e s s f u l may be summarised as f o l l o w s :a)
t h e m a t e r i a l s used were i n s u f f i c i e n t l y p u r i f i e d ( i n
Chapter 1 t h e Importance o f monomer p u r i t y was emphasised),
and
b)
I n s u f f i c i e n t e f f o r t was made t o o p t i m i s e s o l u t i o n
c o m p o s i t i o n s f r o m t h e p o i n t o f view o f r e a c h i n g a
s a t i s f a c t o r y compromise between t h e demands o f monomer
and polymer s o l u b i l i t y and t h e p r o v i s i o n o f s u f f i c i e n t
H donor c a p a c i t y .
Some o f t h i s work was s u b s e q u e n t l y repeated
I n these l a b o r a t o r i e s
u s i n g t h e same c o n d i t i o n s as r e p o r t e d by t h e e a r l i e r
workers
( H i g g i n s g r o u p ) , t h e y had s t a t e d t h a t a 50/50 V/V m i x t u r e o f benzene
i s o p r o p a n o l p r o v i d e s t h e optimum s o l v e n t system f o r these r e a c t i o n s ,
19
y e t when Andrews
repeated
conditions, a substantial
t h e i r work under a p p a r e n t l y
identical
Improvement I n D.P. was observed,
perhaps a b e t t e r momomer p u r i t y .
indicatl
For example t h e I r r a d i a t i o n o f
m-dlbenzoyl benzene I n a I
: 1 benzene : Isopropanol m i x t u r e gave
Andrews a p r o d u c t w i t h a
= 4800, whereas t h e e a r l i e r w o r k e r s
had o b t a i n e d a p r o d u c t w i t h M
%
= 825.
In an a t t e m p t t o o p t i m i s e t h e
a t t a i n a b l e D.P.'s f o r such systems, Andrews i n v e s t i g a t e d t h e e f f e c t
of varying t h e s o l u t i o n compositions.
He observed t h a t use o f a
benzene/isopropanol r a t i o between 3 : 1 and 4 : 1 r e s u l t e d
Ina
marked improvement, In t h a t no p r e c i p i t a t i o n o c c u r r e d d u r i n g
i r r a d i a t i o n and a f a s t e r r a t e o f disappearance o f c a r b o n y l
s o l u t i o n s w i t h t h e h i g h e r r a t i o o f benzene.
also a s i g n i f i c a n t
i n those
G e n e r a l l y t h e r e was
improvement I n m o l e c u l a r weight
(Table 2 . 3 ) .
T h i s improvement may be due I n p a r t t o a r e d u c t i o n i n t h e importance
of t e r m i n a t i o n v i a c o u p l i n g w i t h t h e isopropanol
radicals.
M o l e c u l a r Weights, Degrees o f P o l y m e r i z a t i o n o f P o l y b e n z o p i n a c o l s
19
Prepared i n 1 : 1 and 3 : 1 - 4 ; 1 Benzene-Isopropanol M i x t u r e s
T a b l e 2.3
M o l e c u l a r Weight (D.P.)
Polymer
1:1
Polypinacol
"
"
"
ii
"
M
P
E
1
2
3
4
5
6
10
4800
1300
3400
950
2700
2300
3500
9100
10300
12600
3:1-^:1
14700
3700
4400
7900
2k.
Where t h e f o l l o w i n g monomers used were
Abbrevlat ion
m - dlbenzoylbenzene
M
(ie
Ha)
p - dlbenzoylbenzene
i
kk
dibenzoyldlphenyl ether
•
kk
d i b e n z o y l d i p h e n y l methane
P
(le
lib)
E
(le
He)
1
(le
Hd)
(ie
He)
t
t
ethane
2
= dibenzoyldiphenyl
propane
3
( M
-
dibenzoyldiphenyl
butane
4
1.5 -
( M
-
dibenzoyldlphenyl
pentane
5
1.6 -
(ii.ii
-
djbenzoyldiphenyl
hexane
6
1,10
(4,4
- dibenzoyldiphenyl
decane
10
-
< M
-
1.3 -
( M
1,4-
1.2
dibenzoyldiphenyl
Andrews' r e s u l t s showed t h e p o t e n t i a l o f t h i s approach t o t h e
s y n t h e s i s o f h i g h molecular w e i g h t p o l y p i n a c o l s a l t h o u g h
d i d not c a r r y o u t a d e t a i l e d o p t i m i z a t i o n o f t h e
he
experimental
variables.
The
b e s t r e s u l t s t o date i n t h i s f i e l d were o b t a i n e d
by
18
De Schryver
and co-workers
a f t e r careful consideration of
the
d e t a i l s o f benzophenone p h o t o r e d u c t I o n as e l u c i d a t e d by Weiner
and d i s c u s s e d
i n S e c t i o n 2.3.
I t I s c l e a r t h a t any
combination of the dlphenyl k e t y l
in-cage
r a d i c a l and t h e r a d i c a l
d e r i v e d f r o m t h e hydrogen donor m o l e c u l e I s c h a i n t e r m i n a t i n g
as f a r as s t e p - g r o w t h p h o t o p o l y m e r i z a t i o n i s concerned ( 2 . 1 6 ) .
OH
OH
\
I
\
6 if
"
" 6 4' 7 6 it" & 5
( 3)
Ph
Ph
U
OH OH
OH
OH
I
I
i
i
C
X
C
C -CH.
{ - f - 6 i f J 6V f
Ph
Ph
Ph
CH,
(2.16)
1
c
H
C
C
c
H
x
c
H
C 0 C
H
+
C H
C H 0 H
2
6V
C
H
Chain t e r m i n a t i o n w i t h i s o p r o p a n o l as donor
The
Belgian's
s o l u t i o n t o t h i s problem was
t h e s i m p l e and
elegant
s t e p o f making t h e hydrogen donor a monomer f o r t h e p o l y m e r i z a t i o n .
25.
Thus, when an a p p r o p r i a t e d i k e t o n e and a b I s b e n z h y d r o l a r e
l r r a d l a t e d , t h e t r i p l e t c a r b o n y l a b s t r a c t s a hydrogen atom from
a b e n z h y d r o l u n i t t o generate a s o l v e n t caged p a i r o f d i a r y l
ketyl radicals
OH
(2.17).
OH
These r e s u l t s a r e d i s c u s s e d
\
C
f" f - 6 V t W
W
Ph
below.
X
0 C
H
6 5
Ph
OH
OH
C^-CH-C^-j-X-CgH^- C - i> - ^ n ^ - J —
6
OH
OH
\
OH
( 2
1 ? )
Ph Ph
OH OH
OH
C -C,H
Ph
Ph
/
Ph Ph
n
Ph
Ph
Chain e x t e n s i o n r e s u l t i n g from use o f b i s b e n z h y d r o l as H-donor
and
2.4
monomer
b) R e s u l t s o f De Schryver and co-workers on t h e p h o t o r e d u c t i v e
polymerization o f diketones
De s c h r y v e r and co-workers s t u d i e d two t y p e s o f a r y l
namely bisbenzophenones and b i s k e t o t r i a z o l e s .
ketones,
They a l s o used
two t y p e s o f H-donor system, namely i s o p r o p a n o l , and bisbenzhydrols d e r i v e d from the bisketones;
i n t h e l a t t e r case t h e donor
i s a l s o a comonomer f o r t h e p o l y m e r i z a t i o n .
Their results
t h e c o n v e n t i o n a l isopropanol H-donor system w i l l
with
be c o n s i d e r e d
first.
The monomers used I n t h e i n v e s t i g a t i o n s o f t h e B e l g i a n group
a r e shown below ( 2 . 1 8 ) .
OH
OH
(CH ) CHOH/C H^ , ,
3
C,H jC0ArC0C,H
*> i>
5
J
2
C
6
hv
,
6
\—
T _ £ 4 - C - Ar - C
\i
I
C
H
C
6 5
m
H
6 5/n
(2.18)
26.
N—N
b
NoN
1-
Ar - —^y^ (CH ),—^ ^—
Ar
:
N
Me
Me
(2.18)
N«=.N
d
A r —
e
A r
h Ar- -
^ - ( C H . . ) , - C V - ^ Me
@-<CH,), -^0
f Ar - — < C H A — N
Mc
v
Mc
^ —
Mc
Me
Photoreductive polymerization w i t h diketoneisopropanol-benzene systems
2.k.
Some o f t h e i r r e s u l t s a r e summarized i n T a b l e
T a b l e l.h
Me CH0H
2
Monomer
b
c'
d
f
9
h
[M] mple/1
0.23
0.05*+
0.3
0.17
0.17
0.1
0.5
C
H
6 6
1 5
1 5
1- 3
1 3
1 •3
I •3
1 •3
1 r r a d i a t ion
t ime
7
k
h
4
5
5
2
days
days
days
hours
hours
hours
days
N
M
0.06
0.27
0.23
0.32
0.26
0.19
0.28
82,200
-
69,000
Several p o i n t s a r e w o r t h y o f n o t e i n t h e s e r e s u l t s .
M
n
The
v a l u e s quoted a r e f o r h i g h m o l e c u l a r w e i g h t f r a c t i o n s o b t a i n e d
after fractional precipitation of the i n i t i a l
product; thus, f o r
example, t h e p o l y p l n a c o l d e r i v e d f r o m monomer H f
w e i g h t o f 12,000 as i n i t i a l l y
isolated
and a f t e r
had a m o l e c u l a r
reprecipitation
gave a f r a c t i o n w i t h a m o l e c u l a r w e i g h t o f 82,000.
This
group
c o n f i r m t h e o b s e r v a t i o n o f Pearson and Andrews t h a t s o l v e n t
systems r i c h i n benzene g i v e h i g h e r m o l e c u l a r w e i g h t p r o d u c t s
t h a n t h e 1 : I s o l v e n t system advocated
by H i g g t n s ; a l s o i t i s
c l e a r t h a t w i t h a p p r o p r i a t e monomers p r o d u c t s can be i s o l a t e d
of
r e a s o n a b l y h i g h m o l e c u l a r w e i g h t which c o n f i r m s Andrews'
r e s u l t s u s i n g monomers o f t h e t y p e C ^ H ^ C 0 - ^ ^ ^ - ( C H ) ^ ^ 3 ^ "
C 0 C
2
6 c
where n - 1 ( M = l 4 , 7 0 0 ) , n « 6 (M =10,300) and n - 10
n
(M =12,600).
n
n
U n f o r t u n a t e l y , d i r e c t comparisons between t h e
r e s u l t s o f t h e d i f f e r e n t groups o f w o r k e r s a r e d i f f i c u l t
s i n c e some have used m a i n l y s o l u t i o n v i s c o s i t y and some m a i n l y
molecular weight t o c h a r a c t e r i z e t h e i r v a r i o u s products.
However, c o n s i d e r a t i o n o f t h e r e s u l t s a v a i l a b l e f r o m a l l t h e
workers
I n t h e f i e l d shows t h a t t h e h i g h e s t m o l e c u l a r w e i g h t
samples were i n v a r i a b l y o b t a i n e d u s i n g momomers where t h e two
a r o m a t i c ketone chromophores were s e p a r a t e d f r o m each o t h e r by
the
presence o f a t l e a s t one s a t u r a t e d carbon atom; I n t h e one
example common t o a l l f o u r groups t h e r e was complete agreement
t h a t a h i g h m o l e c u l a r w e i g h t polymer was n o t formed on photor e d u c t i o n o f p - dibenzoylbenzene, t h e r e s u l t s f o r I r r a d i a t i o n o f
t h i s momomer i n benzene-Isopropanol s o l u t i o n a r e summarized
below.
In t h i s p a r t i c u l a r example t h e two c a r b o n y l f u n c t i o n s
a r e c o m p l e t e l y c o n j u g a t e d w i t h each o t h e r , f t i s a l s o
t h a t t h e lowest t r i p l e t
Worker
Higgins
Pearson
Andrews
De Schryver
i s 7 T TV i n c h a r a c t e r f o r t h i s
t
Benzene: I sopropanol
1:1
3:1
1:1
5:1
M
435
1570
1300
-
likely
system.
"ft
0.06
0.06
One f u r t h e r p o i n t o f importance emerged f r o m t h e 'H n.m.r.
e x a m i n a t i o n o f t h e low m o l e c u l a r w e i g h t f r a c t i o n s o b t a i n e d by
the
B e l g i a n group, t h i s was t h e c l e a r d e m o n s t r a t i o n o f t h e
presence o f end groups d e r i v e d f r o m t h e in-cage r e a c t i o n o f
acetone k e t y l r a d i c a l s w i t h t h e d i p h e n y l k e t y l
radicals,
this
H
28.
c o n f i r m s t h a t t h i s minor r e a c t i o n does a c t as a c h a i n t e r m i n a t i o n
process
i n these systems.
The i r r a d i a t i o n o f a d i k e t o n e - d i b e n z h y d r o l m i x t u r e i n benzene
y i e l d e d high molecular weight p o l y p i n a c o l s .
The g r e a t
advantage o f t h i s system i s t h e avoidance o f a cage r e a c t i o n ,
w i t h Me C0H
2
f
which c o n s t i t u t e s c h a i n t e r m i n a t i o n .
Where t h e d i b e n z h y d r o l used f o r t h i s t y p e o f p h o t o r e d u c t i o n
p o l y m e r i z a t i o n i s t h e p r o d u c t o f t h e d i k e t o n e monomer homopolymers a r e o b t a i n e d , whereas when t h e d i b e n z h y d r o l
is derived
from a d i f f e r e n t d i k e t o n e r e g u l a r a l t e r n a t i n g copolymers a r e
formed.
T h i s c o n t r a s t s w i t h t h e s i t u a t i o n o b t a i n i n g when
mixtures o f diketones a r e i r r a d i a t e d
i n benzene-isopropanol
s o l u t i o n which g i v e s r i s e t o s t a t i s t i c a l copolymers.
Some
r e s u l t s o f t h e B e l g i a n group w i t h t h i s system a r e presented i n
T a b l e 2.5., t h e b e n z h y d r o l s JL
listed
by r e d u c t i o n o f t h e d i k e t o n e s
quoted
i n the table are derived
d i s c u s s e d above (see 2.17).
values were measured f o r t h e h i g h m o l e c u l a r
The
weight
Photopolymerlzatlon o f B l s a r y l Ketone-Blshydrol S o l u t i o n
T a b l e 2.5
Ketone
Hydro1
[ M ] , mole/1
III
ni
Ui
El
Hi
Ef
ng
Vb
Vc
Vd
Ve
VI
Vi
Vi
0.1
0.17
0.17
0.013
0.3
0.17
0.17
f r a c t i o n s o b t a i n e d by f r a c t i o n a l
Irradiation
t ime
4
5
5
4
4
4
5
days
days
days
days
days
hours
hours
M
93,500
174,000
141,000
140,000
[n]
0.08
0.21
0.18
0.33
0.36
0.43
0.43
precipitation of the i n i t i a l
product.
S a t i s f a c t o r i l y h i g h m o l e c u l a r w e i g h t s and/or v i s c o s i t i e s
were o b t a i n e d f o r a l l cases except
the
t h a t where t h e benzhydrol was
p r o d u c t r e s u l t i n g f r o m r e d u c t i o n o f p - d i b e n z o y l benzene;
t h a t I s t h e r u c t i o n (2.19).
CH
C,H C0-<O)—C
5
L.
C H
OH
(OV-COC^H,- + HC—/(j)—CH
c
6
OH
3
\ ~ /
6
L . X^/
6 5
5
C
3
i ..
6 5
H
C
(2
__hy_copoly
benzene P'nacol
>
H
- y i e l d i n g a p r o d u c t o f very much lower
v i s c o s i t y than a l l o t h e r cases
2.5
solution
investigated.
OBJECTIVES OF PRESENT RESEARCH
In t h i s work i t was intended t o use s t e p - g r o w t h p h o t o r e d u c t I v e
p o l y m e r i z a t i o n as t h e f i r s t stage i n t h e s y n t h e s i s o f novel
polymers.
aromatic
The o v e r a l l o b j e c t i v e s o f t h e work a r e summarized below.
Stage 1 P r e p a r a t i o n o f P o l y b e n z o p l n a c o l S t a r t i n g M a t e r i a l s .
The f i r s t
of
s t e p i n t h e p r o j e c t e d work i n v o l v e d t h e s y n t h e s i s
t h e f o l l o w i n g p o l y b e n z p i n a c o l s ( 2 1 & 3ZH ) f r o m t h e f o r e g o i n g
OH OH
OH OH
Ph Ph.
•n
oi
w
1
OH OH
W - ® - H Ph Ph
3ZL
Ph Ph
m
d i s c u s s i o n two approaches t o t h e s y n t h e s i s a r e p o s s i b l e depending
on whether i s o p r o p a n o l o r a d i b e n z h y d r o l
i s used as t h e hydrogen
donor, p r e v i o u s work Imples t h a t t h e l a t t e r method o f f e r s t h e best
chance o f o b t a i n i n g h i g h m o l e c u l a r w e i g h t p r o d u c t s and t h i s
approach was I n v e s t i g a t e d f i r s t .
The d i ketone,
benzene, was I r r a d i a t e d w i t h t h e met a-and
and JZ..
m- d i b e n z o y l -
p - d i benzhydrol s 3ZQI
Due t o t h e poor s o l u b i l i t y o f t h e m- and p - b i s b e n z h y d r o l s ,
OH
OH
2m
OH
OH
JX
30.
t h r e e s e t s o f c o n d i t i o n s were used i n t h i s p r e v i o u s l y u n i n v e s t i g a t e d
react ion.
i)
m-Dibenzoyl benzene d i s s o l v e d i n benzene a t room
temperature i n t h e presence o f e i t h e r u n d i s s o l v e d m- o r
p-bfsbenzhydrol w a s - i r r a d i a t e d w i t h t h e i n t e n t i o n o f a l l o w i n g t h e
d i o l t o d i s s o l v e as t h e r e a c t i o n proceeded.
T h i s t e c h n i q u e was
used s u c c e s s f u l l y by t h e B e l g i a n group w i t h d i f f e r e n t monomers.
II)
m-Dibenzoyl benzene d i s s o l v e d i n h o t benzene w i t h
m- o r p - b i s b e n z h y d r o l was I r r a d i a t e d .
The use o f a f i l t e r
s o l u t i o n was l a t e r i n c o r p o r a t e d i n t o t h i s experiment
t h a t unwanted r a d i a t i o n a t wavelengths
either
t o ensure
lower than 350 n.m. was
excluded.
iii)
I r r a d i a t i o n o f m-dibenzoyl benzene d i s s o l v e d i n a c e t o n i t r i i e
a t room t e m p e r a t u r e w i t h m- o r p- b i s b e n z h y d r o l ; b o t h monomers
being r e a d i l y s o l u b l e .
Since none o f these procedures
polymers
yielded high molecular
weight
t h e p h o t o r e d u c t i v e p o l y m e r i z a t i o n o f m-dibenzoyl benzene
i n isopropanol-benzene
optimise M
s o l u t i o n was i n v e s t i g a t e d
i n an a t t e m p t t o
f o r polymer 3ZE .
Stage 2 C a t a l y t i c D e h y d r a t i o n o f Polybenzopinacol S t a r t i n g
Material.
Having made a p o l y b e n z o p i n a c o l w i t h a reasonable m o l e c u l a r
weight
t h e next i n t e n d e d s t e p was t h e a c i d c a t a l y z e d d e h y d r a t i o n o f t h e
polybenzopinacol
involving a pinacol-pinacolone
rearrangement
(2 .20) .
OH
Ph
OH
i)
I)
Ph
Ph
ii)
II
D.M.S.O./benzene
T^/CH-COOH
O
C.H S0./p-dioxane
Ph
o
HI
(2 .20)
Ph
m
n
31.
Two p o s s i b l e p r o d u c t s may be produced depending on whether
c h a i n m i g r a t i o n o r phenyl m i g r a t i o n takes p l a c e .
d i f f i c u l t y encountered
The
w i t h t h i s r e a c t i o n i s degradation of the
polymer and whether d e h y d r a t i o n t a k e s p l a c e a t a l l d e s p i t e t h e
f a c t t h a t t h e model monomer can be r e a d i l y c o n v e r t e d
t o t h e ketone:
hence s e v e r a l methods were t r i e d .
Stage 3 Reduction
o f Polybenzopinacolone
O R
(X XI)
u s i n g NaBH^.
] k-
T h i s r e a c t i o n c o u l d be c a r r i e d o u t i n e i t h e r t o l u e n e o r
dioxan
t
(2.21).
OH
Ph
Ph
II
Ph
Ph
(2 .2
Ph
Ph
OH
H
Ph
Ph
Stage k D e h y d r a t i o n o f Polymers ~XJL and/or H E
.
F i n a l l y , a c i d c a t a l y z e d dehydration o f the products t o g i v e
polymersZEST a n d / o r X E (2 . 2 2 ) .
m
OH
Ph
\
Ph
\
Ph
Ph
zn
(2.2
Ph
H
Ph
Ph
OH
II
Ph
XTTT
The l i k e l y properties of polymers with the novel structures
X E a n d S S a r e d i f f i c u l t to predict; but in recent years
considerable efforts have gone into attempts to synthesise
totally conjugated aromatic and heteroaromatic polymers.
CHAPTER 3
SYNTHESIS OF MONOMERS, THEIR PHOTOPOLYMER IZATION
AND SUBSEQUENT REACTIONS
33
PART 1.
3.1
MONOMERS
The F r i e d e l - C r a f t s R e a c t i o n
T h i s r e a c t i o n was
used I n t h e p r e p a r a t i o n o f m-d I benzoyl benzene,,
t h e p r i n c i p a l monomer r e q u i r e d f o r t h i s work.
Friedel-Crafts
r e a c t i o n s can be d i v i d e d i n t o two g e n e r a l t y p e s namely a l k y l a t i o n
and a c y l a t l o n s .
(3.1).
f o l lowing
CH CK Br
3
2
An example o f a F r i e d e l - C r a f t s a l k y l a t i o n i s t h e
A1C1,
^ ! 3 - >
(g)
+
X^yCH CH,
(gf
* +
2
(3.1)
HBr
On t r e a t m e n t w i t h a l e w i s a c i d t h e e t h y l bromide
a f r e e c a r b o n i u m i o n (CH^CH^*) which b e i n g a s t r o n g
3
+
2
A1C1
electrophile
(3.2).
a t t a c k s t h e benzene r i n g
CH CH Br
is converted t o
>
3
C H C H - B r - A l C l 5=£ CH CH
3
2
3
3
2
+ AlCljBr
CH CH2
3
CH CH
3
2
+
»
CH CH,-^>,
_ ^
3
+ HBr
( . )
3
2
HOne o f t h e main disadvantages o f t h e F r i e d e l - C r a f t s a l k y l a t i o n
i s t h a t carbonium
in
i o n rearrangements may
o c c u r , as shown f o r example
3.3.
A1C1
«.
CH CH CH
CHjCh^CHj-Br
3
*
CH ^H-CH
3
2
2
+
2
»
CHJCHCHJ
(3.3)
Hence t h e n - p r o p y l c a t i o n r e a r r a n g e s t o t h e more s t a b l e
cation.
Even i f rearrangement
isopropyl
does not o c c u r , p o l y a l k y l a t i o n
may
and t h e s e f a c t o r s p u t r e s t r i c t i o n s on t h e s y n t h e t i c u t i l i t y o f t h e
reaction.
An improvement on t h i s t y p e o f r e a c t i o n i s t h e F r l e d e l -
C r a f t s a c y l a t i o n i n w h i c h an a c y l i u m i o n i s g e n e r a t e d
(3.4).
3*».
R-cf + A1C1-
[R-C-0 < — »
R-C^O] +
AlClT
(3
3
CI
T h i s r e a c t i o n , however, r e q u i r e s more than one e q u i v a l e n t o f
c a t a l y s t ( A l C l ^ ) because t h e ketone i s b a s i c enough t o f o r m a s a l t
w i t h t h e l e w i s a c i d which reduces t h e c a t a l y t i c a c t i v i t y o f t h e
latter.
it
The most commonly used c a t a l y s t i s aluminium
i s cheap and i t possesses h i g h c a t a l y t i c a c t i v i t y .
c h l o r i d e because
Other c a t a l y s t s
may be employed such as A l B r ^ , F e C l ^ FeBr^, T i C l ^ , NbCl^, Z r C l ^ ,
metal
powders,
iodine etc.
With p a r t i c u l a r r e f e r e n c e t o t h e p r e p a r a t i o n o f m-dibenzoyl benzene
t h e method adopted was an a c y l a t i o n u s i n g i s o p h t h a l o y l c h l o r i d e
with AlCl^
i n t h e presence o f benzene as both reagent
and solvent.
(3.5).
0
II
0
I I
A
J
C
0
I I
1
0
I I
T h i s r e a c t i o n has been e x t e n s i v e l y used by o t h e r w o r k e r s who
reported y i e l d s
I n t h e r e g i o n 20-45%, r e c e n t work i n t h i s department
has a l l o w e d y i e l d s o f pure m a t e r i a l t o be c o n s i d e r a b l y i n c r e a s e d , t h e
experimental
3.2
d e t a i l s are reported
Grignard
Reagents
Grignard
reagents
later.
(organomagnesium compounds, prepared
o r g a n i c hal ides and magnesium) a r e amongst the- most u s e f u l
available.
from
reagents
A common method f o r t h e p r e p a r a t i o n o f an o r g a n o m e t a l 1 i c
compound i s by r e a c t i o n o f an o r g a n i c h a l i d e w i t h a m e t a l .
The
r e a c t i v i t y o f t h e r e s u l t i n g o r g a n o m e t a l 1 i c compound increases w i t h
t h e percent o f i o n i c c h a r a c t e r o f t h e carbon t o metal
bond.
An
35.
o r g a n i c h a l l d e and magnesium r e a c t i n e t h e r t o f o r m what i s o f t e n
r e p r e s e n t e d as R-Mg-X though
the complex.
t h i s formula i s a s i m p l i f i e d form o f
T e t r a h y d r o f u r a n i s a l s o commonly used i n t h e
p r e p a r a t i o n o f G r i g n a r d reagents.
Since t h e carbon
t o magnesium
bond i s p o l a r i s e d w i t h p a r t i a l n e g a t i v e c h a r g e o n R o r X, rearrangements
of
t h e carbonium i o n t y p e a r e not common.
a G r i g n a r d reagent
The advantage o f making
i s i t s a b i l i t y t o react w i t h a carbon-heteroatom
m u l t i p l e bond, f o r example an aldehyde o r k e t o n e , whereby a complex
magnesium a l k o x i d e i s formed f r o m w h i c h t h e a l c o h o l may be l i b e r a t e d
by t h e a d d i t i o n o f d i l u t e a c i d ( 3 . 6 ) .
OH
(3.6)
R
In t h e case o f p r e p a r i n g p - b i s b e n z h y d r o l
i n t e n d e d f o r use i n t h e
p h o t o r e d u c t i o n o f m-dibenzoyl benzene, t h e G r i g n a r d
reagent was f i r s t
prepared by r e a c t i n g bromobenzene w i t h magnesium t u r n i n g s i n d i e t h y l
e t h e r , t e r e p h t h a l d e h y d e was then added t o g i v e ( a f t e r h y d r o l y s i s ) t h e
(3.7) •
f i n a l product
OMgBr
®
"
B
r
d
f e
ether
<Q)-^
Br
terephth- >
aldehyde
j*
H 0/H
,
OMgBr
™~(<5><»>
H
H
, OH
OH
2
H
The f i r s t
may
1
—'
a t t e m p t a t t h i s s y n t h e s i s gave a y e l l o w o i l y wax which
be a s c r i b e d t o a d e h y d r a t i o n p r o d u c t o f s t r u c t u r e
OH/
H
\
OH
Ph-C4\OVCHOCH -HO)-C-Ph
1
Subsequent p r e p a r a t i o n s gave t h e expected
product.
(3.7)
36.
3.3
Sodium B o r o h y d r i d e Reduction o f meta-Dibenzoylbenzene
Complex metal h y d r i d e s o f f e r t h e most c o n v e n i e n t method f o r t h e
r e d u c t i o n o f aldehydes
and ketones t o t h e c o r r e s p o n d i n g a l c o h o l s .
The most commonly used reagents a r e l i t h i u m aluminium h y d r i d e and
sodium b o r o h y d r i d e .
The l a t t e r i s a much m i l d e r r e d u c i n g agent used
i n e t h a n o l o r aqueous e t h a n o l , under which c o n d i t i o n s i t w i l l
reduce
aldehydes
rapidly
and ketones, b u t i s i n e r t towards most o t h e r
f u n c t i o n a l groups.
The p r e p a r a t i o n o f m-blsbenzhydrol
( l , 3 - b i s ( o t - h y d r o x y b e n z y l ) benzene) was c a r r i e d o u t i n t h i s way t o
g i v e t h e t h i r d and f i n a l monomer.
The r e a c t i o n was s t r a i g h t f o r w a r d
and e x p e r i m e n t a l d e t a i l s a r e p r e s e n t e d below.
3.4
Experimental
a)
P r e p a r a t i o n o f m-dibenzoyl benzene ( F r i e d e l - C r a f t s )
To a s t i r r e d s o l u t i o n o f i s o p h t h a l o y l c h l o r i d e (55 grms.,
0.271
ide
moles) i n d r y benzene (400 m i s ) , anhydrous a l u m i n i u m
chlor-
(80 grms., 0.6 moles) was added i n s m a l l p o r t i o n s as a
crushed powder.
Initially
the reaction
proceeded
s p o n t a n e o u s l y due t o e x o t h e r m i c ! t y , a f t e r which t h e i s o m a n t l e
was used t o m a i n t a i n t h e s o l v e n t a t r e f l u x .
The s o l u t i o n went
f r o m a l i g h t brown c o l o u r t o a d a r k brown-green.
The r e a c t i o n
o c c u r r e d o v e r a p e r i o d o f a p p r o x i m a t e l y two hours.
A f t e r c o o l i n g t h e m i x t u r e was removed f r o m t h e f l a s k
3 necked R.B.) and added t o a l a r g e 5 l i t r e c o n i c a l
containing
(2 l i t r e . ,
flask
i c e , w a t e r and a 5% aqueous s o l u t i o n o f sodium
c a r b o n a t e , r a t h e r t h a n t h e HC1 s o l u t i o n u s u a l l y advocated.
The
r e s u l t i n g m i x t u r e i n t h e c o n i c a l f l a s k c o n s i s t e d o f two l a y e r s ,
the
lower one b e i n g t h e aqueous l a y e r which c o n t a i n e d a m i l k y
w h i t e p r e c i p i t a t e o f aluminium h y d r o x i d e .
The t o p l a y e r
c o n t a i n i n g benzene p l u s p r o d u c t was orange i n c o l o u r .
At t h i s
s t a g e d i l u t e h y d r o c h l o r i c a c i d was added which d i d l i t t l e t o t h e
37.
r e a c t i o n m i x t u r e except a l l o w i n g t h e aluminium h y d r o x i d e t o go
Into solution.
evaporated,
dissolved
The two l a y e r s were s e p a r a t e d and t h e benzene
leaving a milky white p r e c i p i t a t e .
i n cyclohexane
and d r i e d
T h i s was
(anhydrous MgSO^)» a f t e r
f i i l t r a t i o n t h e h o t s o l u t i o n was a l l o w e d t o c o o l s l o w l y i n a
3 l i t r e round bottomed f l a s k wrapped i n c o t t o n w o o l .
The
process o r r e c r y s t a l 1 i z a t i o n was repeated s e v e r a l t i m e s , each
t i m e two types o f c r y s t a l b e i n g produced;
a prismatic soft
w h i t e c r y s t a l and a harder t a b u l a r c r y s t a l which was t i n g e d
yellow.
E v e n t u a l l y t h e w h i t e f i n e r c r y s t a l l i n e f o r m became
more dominant than t h e y e l l o w coarse
crystals.
A l a r g e r s c a l e p r e p a r a t i o n was l a t e r necessary
where t h e
f o l l o w i n g amounts o f r e a c t a n t were used : 250 grms. (1.23 moles)
isophthaloyl chloride, 2 l i t r e s
of
AlCl^
( f r e s h l y ground).
(1756 grms) benzene and 400 grms
With t h i s preparation the a d d i t i o n a l
p r e c a u t i o n was taken by b o i l i n g t h e p r o d u c t w i t h d e c o l o u r i z i n g
c h a r c o a l f o r 1 hour, t h i s was then removed by f i l t r a t i o n u s i n g
H y f l o i n a Buchner f u n n e l .
This time a l l the c r y s t a l s
recovered
were o f one c r y s t a l l i n e f o r m , i . e . f l a k y and w h i t e ( Y i e l d : 73%,
,€
m.p. 102°-104°C, (1 Iterature 103°, 100°, 110°) .
C, 84.19%; H, 5.26%.
H, 4.93%.
b)
H
C a l c u l a t e d f o r C 0 ]k°2
2
:
Found:
C
8
»
3
'
9
0
%
;
l . r . - Appendix A; 1 ) .
P r e p a r a t i o n o f 1,3-bisfec h y d r o x y b e n z y l ) benzene
Sodium b o r o h y d r i d e (33.3 grms.) was added s l o w l y t o an
e t h a n o l - w a t e r m i x t u r e c o n t a i n i n g m-dibenzoylbenzene (125 grms.,
0.44 m o l e s ) .
The whole system was purged w i t h ^
i n order t o
d i s p e r s e t h e l a r g e amounts o f hydrogen produced i n a r e a c t i o n
of
t h i s type.
A f t e r a l l t h e b o r o h y d r i d e had been added t h e
s o l u t i o n was r e f l u x e d f o r a p p r o x i m a t e l y 45 minutes and, a f t e r
c o o l i n g , excess b o r o h y d r i d e was d e s t r o y e d by c a r e f u l
addition
38.
of d i l u t e h y d r o c h l o r i c a c i d .
T h i s r e q u i r e d 600 mis o f approx-
i m a t e l y 8-10% aqueous HC1 and gave a m i l k y s o l u t i o n .
was
The p r o d u c t
p r e c i p i t a t e d by e v a p o r a t i o n o f p a r t o f t h e e t h a n o l and then
r e c r y s t a l 1 I z e d from ethanol/water.
C, 82.62%; H, 5.96%.
( Y i e l d : 82%,
Calculated f o r C ^ H ^
:
Found:
C, 82 . 731%;
H, 6.248% w i t h c o r r e c t i n f r a r e d spectrum Appendix A; 2 ) .
c)
P r e p a r a t i o n o f l,*+-bIs(oc h y d r o x y b e n z y l ) benzene ( G r l g n a r d r o u t e )
A l l apparatus was d r i e d
i n t h e oven and assembled h o t w h i l e
being flushed w i t h dry n i t r o g e n .
The magnesium t u r n i n g s (97.28 grms.
were covered by a p p r o x i m a t e l y 1.5 l i t r e s o f T.H.F. I n a 3 l i t r e ,
3 necked R.B. f l a s k .
The d r o p p i n g f u n n e l was then f i l l e d
with
3 1 ^ grms. (2 moles) o f bromobenzene, which was added s l o w l y .
i o d i n e c r y s t a l was necessary
smoothly.
t o I n t l t a t e t h e r e a c t i o n which
An
proceeded
The t e m p e r a t u r e range was m a i n t a i n e d a t a p p r o x i m a t e l y
65 - 75 C by t h e r e a c t i o n e x o t h e r m i c ! t y and c o n t r o l o f t h e r a t e o f
addition.
T h i s o p e r a t i o n l a s t e d a p p r o x i m a t e l y 2 hours.
A f t e r t h e s o l u t i o n c o o l e d t o below 30 C, t h e t e r e p h t h a l d e h y d e
(65.0 grms. d i s s o l v e d I n a p p r o x i m a t e l y 0.5 l i t r e s o f T.H.F.) was
added dropwlse, g i v i n g a d a r k o r a n g e s o l u t i o n which was v i s c o u s a t
room t e m p e r a t u r e .
which
The m i x t u r e was r e f l u x e d f o r 2 hours
after
I t was added t o a l a r g e excess o f a c i d i f i e d c o l d w a t e r .
S t i r r i n g o f t h i s m i x t u r e produced a w h i t e s o l u t i o n c o n t a i n i n g
Mg(0H)
2
which d i s s o l v e d when more a c i d was added.
o f T.H.F. i n water made I t necessary
The s o l u b i l i t y
t o extract with ether u n t i l
f i n a l l y t h e e x t r a c t was t r a n s p a r e n t orange.
E v a p o r a t i o n o f T.H.F.
and e t h e r gave an orange p r e c i p i t a t e which f a i l e d t o r e c r y s t a l I I z e
in a 1 : I ethanol-water mixture.
A f t e r several attempts t o
p u r i f y t h i s p r o d u c t I t was assumed t h a t t h e d l o l had n o t been
r e c o v e r e d and t h a t p o s s i b l y an excess o f a c i d had been i n t r o d u c e d
d u r i n g t h e work-up w h i c h may have f a c i l i t a t e d an a c i d c a t a l y z e d
39.
dehydration,
The p r e p a r a t i o n was repeated;
t h i s time t a k i n g
p a r t i c u l a r c a r e t o add t h e a c i d I n small q u a n t i t i e s and keep
t h e m i x t u r e a t ambient t e m p e r a t u r e
d u r i n g t h e work up;
r e c r y s t a l 1 i z a t l o n I n a w a t e r : e t h a n o l m i x t u r e (1 : k) gave
f i n e white crystals.
( Y i e l d ; 67%; Found; C, 82.60 %;
H, 6.2%; C a l c u l a t e d f o r C ^ H ^
correct
PART 2.
3.5
: C, 82 . 73%;
H, 6.25 % w i t h
l . r . - Appendix A; 3 ) .
POLYMERIZATIONS
P r e p a r a t i o n o f t h e S o l u t i o n s t o be
Irradiated
The monomers used I n t h e f o l l o w i n g experiments
were d r i e d on t h e
vacuum l i n e (ca. 1 day a t 10
m.m. Hg) and t h e benzene was r e f l u x e d
o v e r sodium and then d i s t i l l e d
p r i o r t o use.
procedures were adopted !n t h e a t t e m p t e d
The f o l l o w i n g
p h o t o r e d u c t i o n o f m-dIbenz-
o y l benzene.
I.
I r r a d i a t i o n o f meta-dIbenzoyl benzene and e i t h e r 1,3 o r \,h
bis
-
(oChydroxybenzyl) benzene i n benzene s o l u t i o n
Equimolar q u a n t i t i e s o f d i k e t o n e and b i s b e n z h y d r o l were weighed
out
I n t o I r r a d i a t i o n vessels
( l o n g pyrex tubes ca. 1 cm. d i a m e t e r )
and s u f f i c i e n t d r y benzene added t o make s o l u t i o n s 0.1 M I n each
monomer.
Only t h e d i k e t o n e d i s s o l v e d c o m p l e t e l y under these c o n d i t i o n s .
The m i x t u r e was streamed w i t h n i t r o g e n t o remove t h e p o s s i b i l i t y o f
r e s i d u a l oxygen quenching t h e c a r b o n y l t r i p l e t s ;
stopped
lamps).
and i r r a d i a t e d
t h e tubes were
In a Rayonet Photochemical Reactor (350 n.m.
I t was hoped, f o l l o w i n g t h e precedent
o f the reported
B e l g i a n work, t h a t as t h e r e a c t i o n proceeded t h e d i o l monomer would
d i s s o l v e ; however, a f t e r s e v e r a l days t h e o n l y o b s e r v a b l e
change was
the yellowing o f the s o l u t i o n .
spectroscopy
of
An a n a l y s i s by i n f r a r e d
t h e s o l i d recovered a f t e r e v a p o r a t i o n o f s o l v e n t i n d i c a t e d t h a t no
r e a c t i o n had o c c u r r e d ;
i t was concluded
t h a t t h e d i o l monomers were
too
I n s o l u b l e t o a l l o w t h e g r a d u a l d i s s o l u t i o n process r e p o r t e d by
the
B e l g i a n group t o o p e r a t e I n t h i s
case.
In an a t t e m p t t o o b t a i n homogeneous s o l u t i o n s o f b o t h monomers
In benzene p r o g r e s s i v e l y h i g h e r d i l u t i o n s were examined; however, t h e
d i l u t i o n s required f o r s o l u b i l i t y
(ca 0.008 M) I n v o l v e d
Inconveniently
small q u a n t i t i e s o f monomer and l a r g e volumes o f benzene.
Even t h e n
t h e r e was no d e t e c t a b l e r e a c t i o n a f t e r i r r a d i a t i n g f o r p r o l o n g e d (COL 1 u > t e k
p e r i o d s ; f o r example, t h e I n f r a r e d spectrum o f t h e s o l i d r e c o v e r e d
a f t e r I r r a d i a t i o n o f a 0.0077 M s o l u t i o n o f meta-dIbenzoyl benzene
and 1, 3-bts («*. hydroxybenzyl) benzene I n benzene I s shown I n
Appendix A, No. k and I n d i c a t e s no a p p r e c i a b l e consumption o f carbony.
Ii,
I r r a d i a t i o n o f meta-dIbenzoyl benzene and 1, 3 b i s (o< hydroxyb e n z y l ) benzene In benzene s o l u t i o n a t r e f l u x
Since b o t h monomers were f o u n d t o be s o l u b l e I n h o t benzene, I t
was decided t o a t t e m p t t h e r e a c t i o n by I r r a d i a t i n g t h e r e f l u x i n g
solution.
The apparatus used f o r e x p e r i m e n t s d e s c r i b e d h e r e I s shown
In diagram 3.1 w i t h accompanying r e f e r e n c e t a b l e .
The use o f a
f i l t e r s o l u t i o n (see (b) below) p r e v e n t s unwanted r a d i a t i o n r e a c h i n g
the
reactants.
The s o l u t i o n e n t e r s t h e r e a c t o r a t 5. and leaves a t
18., when no f i l t e r was used t h i s space was purged w i t h d r y n i t r o g e n .
To t h e two B.19 cones (21.) two d o u b l e w a l l e d condensers were f i t t e d ;
one o f them h a v i n g a
of
the reaction flask.
bleed passing through t h e c e n t r e t o t h e bottom
C i r c u l a t i o n o f t h e f i l t e r s o l u t i o n was a c h i e v e d
by a p e r i s t a l t i c pump which a l s o pumped t h e s o l u t i o n t h r o u g h a s p i r a l
condenser f o r t h e purpose o f keeping I t c o o l .
of
t h e r e a c t o r was enclosed i n a l u m i n i u m f o i l
escape o f harmful U.V.
radiation.
F i n a l l y t h e major
so p r e v e n t i n g t h e
part
a)
The f i r s t a t t e m p t i n v o l v e d i r r a d i a t i n g
1, 3 - b i s («>*hydroxy-
b e n z y l ) benzene (1.45 grms.) and m- d l b e n z o y b e n z y l ) benzene (1.43 grms.)
In 250 mis o f benzene a t r e f l u x f o r s e v e r a l days.
On c o o l i n g t h e
c r y s t a l s which p r e c i p i t a t e d were pure u n r e a c t e d 1, 3 - b i s (oc hydroxyb e n z y l ) benzene ( l . r . - Appendix A; 5) whereas t h e m a t e r i a l
by e v a p o r a t i o n o f s o l v e n t appeared
isolated
t o be a m i x t u r e o f monomers ( l . r . -
Appendix; 6) .
b)
The above experiment was r e p e a t e d under
except f o r t h e i n c o r p o r a t i o n o f a f i l t e r
NaBr
(74.09 grms.) and H g ( N 0 )
3
2
identical
conditions
s o l u t i o n which c o n t a i n e d
(0.25 grms.) d i s s o l v e d I n 250 m i s .
T h i s s o l u t i o n c u t s o u t most o f t h e lamp o u t p u t o f wavelength
ca 310 n.ni.
less than
A l t h o u g h t h e t . l . c . showed t h e presence o f two components
o t h e r than t h e monomers, an i n f r a r e d s p e c t r o s c o p i c a n a l y s i s o f t h e
s o l i d p r o d u c t from t h i s r e a c t i o n
(Appendix A; 7) i n d i c a t e d an a l m o s t
I n s i g n i f i c a n t consumption o f c a r b o n y l .
Attempts t o separate t h e
components o f t h e p r o d u c t by column chromatography proved u n s u c c e s s f u l
because a s u i t a b l e s o l v e n t c o u l d n o t be f o u n d .
The r e a c t i o n between
m-di benzoyl benzene and 1,4 - b i s («* h y d r o x y b e n z y l ) benzene was n o t
a t t e m p t e d I n view o f t h e f a i l u r e o f t h e a t t e m p t w i t h t h e meta
III.
Isomer.
Reactions i n a c e t o n i t r l l e as s o l v e n t
A c e t o n l t r i l e was found t o d i s s o l v e a l l t h e monomers I n v o l v e d I n
t h i s work.
The a c e t o n l t r i l e used was d i s t i l l e d f r o m
using a
f r a c t i o n a t i n g column (80 cms x 2 cms) c o n t a i n i n g g l a s s h e l i c e s .
Two s o l u t i o n s (0.066 M and 0.0025 M) o f t h e monomers I n f r e s h l y
d i s t i l l e d a c e t o n i t r l l e were p r e p a r e d i n c y l i n d r i c a l
f i t t e d w i t h t e f l o n Rotaflow taps.
vacuum l i n e
reaction vessels
The s o l u t i o n s were degassed on a
(10 m.m. Hg) by t h r e e f r e e z e - t h a w c y c l e s , a f t e r which
t h e y were l e t down t o a t m o s p h e r i c p r e s s u r e under t h e presence o f d r y
nitrogen.
The tubes were I r r a d i a t e d
i n a Rayonet Reactor
U IAUKAM j.I
1.
2.
3.
h.
5.
6.
7.
8.
9.
10.
11.
12.
13.
\h.
1516.
17.
18.
19.
20.
21.
22.
232k.
25.
26.
Pyrex f l a s k
Outer q u a r t z J a c k e t
Inner q u a r t z j a c k e t
U shaped tube I s low p r e s s u r e
S t r a i g h t t u b e I s medium p r e s s u r e
C o o l i n g w a t e r o r gas f l u s h I n l e t
A r c t u b e s u p p o r t tube
Rubber s l e e v e .
I n l e t and o u t l e t f o r gas f l u s h o n l y
E a r t h t e r m i n a l f o r a r c t u b e s u p p l y c a b l e green c o r e
Two ceramic I n s u l a t e d t e r m i n a l s f o r a r c tube power s u p p l y
red and b l a c k c o r e s
Terminal cover
\
Cable clamp
I n l e t f o r supply cable
Terminal b l o c k
2 screws t o r e t a i n t e r m i n a l c o v e r
Rubber s l e e v e clamps
Ceramic I n s u l a t e d leads f r o m t e r m i n a l s t o a r c tube
C o o l i n g w a t e r o r gas f l u s h o u t l e t
BAO cone and socket
B^5 cone and socket
B19 cone and socket
Reagent l e v e l t o p e r m i t gas f l u s h above reagent
Space f o r gas f l u s h o n l y
Arc tube s u p p o r t c l i p s
Space f o r c o o l i n g water o r gas f l u s h
Space f o r magnetic s t i r r e r
10
11
**3.
(3500 A tamps) f o r 55 hours and t h e p r o d u c t recovered by e v a p o r a t i o n
of the solvent.
The
I n f r a r e d spectra o f the products
(Appendix
A,
8 and 9 r e s p e c t i v e l y ) I n d i c a t e d t h a t a g a i n I n s i g n i f i c a n t c a r b o n y l
consumption had o c c u r r e d .
a check on t h e t e c h n i q u e ;
This very d i s a p p o i n t i n g r e s u l t
prompted
I r r a d i a t i o n o f an e q u l m o l a r s o l u t i o n o f
benzophenone and b e n z h y d r o l
I n a c e t o n t t r t l e under t h e same c o n d i t i o n s
gave benzoplnacol q u a n t i t a t i v e l y , t h e I n f r a r e d spectrum o f t h e t o t a l
recovered p r o d u c t I s shown I n Appendix A;
10.
The d i s a p p o i n t i n g outcome o f t h e a t t e m p t e d
polymerizations
d e s c r i b e d above f o r c e d t h e a u t h o r t o examine t h e o p t i m i z a t i o n o f t h e
r e d u c t i v e p h o t o p o l y m e r i z a t i o n o f meta-d(benzoylbenzene u s i n g
Isopropanol
as hydrogen donor.
3.6
P h o t o r e d u c t i o n o f m-dIbenzoylbenzene I n Benzene :
Isopropanol
Mixtures
I.
Experimental
The
I n v e s t i g a t i o n o f t h e optimum c o n d i t i o n s under w h i c h a h i g h
m o l e c u l a r w e i g h t p o l y b e n z o p l n a c o l may
i s o p r o p a n o l as a donor was
experiment was
be formed i n t h e presence o f
attempted.
r u n a f t e r which
F i r s t l y , a preliminary
s i x tubes were p r e p a r e d , c o n t a i n i n g
v a r y i n g benzene I s o p r o p a n o l m i x t u r e s and
Irradiated.
The
solid
p r o d u c t s were i s o l a t e d by e v a p o r a t i o n o f t h e s o l v e n t and t h e i r r e s p e c t i v e
m o l e c u l a r w e i g h t s were t h e n
a)
Experiment 1
I n a m i x t u r e o f 12.5
reaction vessel.
determined.
m-Dlbenzoylbenzene (2.1^75 grms.) was
mis I s o p r o p a n o l + 62.5
The
s o l u t i o n was
t o I r r a d i a t i o n a t A = 350
mis benzene i n a c y l i n d r i c a l
n i t r o g e n streamed and t h e n exposed
n.m. f o r 62.2
was o r i g i n a l l y c o l o u r l e s s but a f t e r
dissolved
hours.
The
benzene s o l u t i o n
I r r a d i a t i o n I t was
f a i n t w h i t e p r e c i p i t a t e a t t h e bottom o f t h e t u b e .
yellow with a
The
infrared spectra
o f t h e p r e c i p i t a t e d m a t e r i a l and t h e s o l i d o b t a i n e d on e v a p o r a t i o n o f
t h e s o l v e n t were I d e n t i c a l and showed no c a r b o n y l s t r e t c h i n g
(Appendix
A; 1 1 ) .
b)
Experiment 2
S i x pyrex tubes o f a p p r o x i m a t e l y 100 mis
c a p a c i t y c o n t a i n i n g 3 grms (0.01048 moles) m-dIbenzoylbenzene d i s s o l v e d
I n m i x t u r e s o f benzene and Isopropanol were made up as shown i n t h e
table.
Isopropanol
mis
Benzene
mis
2
3
5
6
10
15
28
27
25
The
Ratio
i s o p r o p a n o l : benzene
1
1
i
1
1
1
2k
20
15
tubes were p l a c e d
a t 350 n.m. f o r one week.
t h e tubes and a l l
:
:
:
:
:
:
No. o f moles
isopropanol
\k
0.026
0.039
0.065
0.079
0.1308
0.196
9
5
A
2
1
I n a Rayonet 'Werry-Go-Round" and i r r a d i a t e d
There was some p r e c i p i t a t i o n
t h e s o l u t i o n s were y e l l o w .
i n some o f
The p r e c i p i t a t i o n was
g r e a t e s t i n t h e tubes c o n t a i n i n g t h e h i g h e r c o n c e n t r a t i o n o f
i s o p r o p a n o l and t h e r e was a g r a d u a l
r e d u c t i o n i n t h e amount o f
p r e c i p i t a t e as t h e I s o p r o p a n o l c o n c e n t r a t i o n decreased.
The tubes
having a 1 : \k and 1 : 9 r a t i o showing no p r e c i p i t a t i o n .
The
p r e c i p i t a t e s were i s o l a t e d by f i l t r a t i o n and t h e s o l u b l e p r o d u c t
recovered
by e v a p o r a t i o n .
The i . r . s p e c t r a o f a l l p r o d u c t s were
v i r t u a l l y t h e same and showed almost c o m p l e t e c a r b o n y l
a t y p i c a l example I s recorded
11.
consumption,
i n Appendix A, No. 12.
M o l e c u l a r Weights o f t h e P o l y b e n z o p i n a c o l s Prepared i n Benzene Isopropanol
a)
Apparatus
The
apparatus
used f o r t h e s e d e t e r m i n a t i o n s was a Model 115
M o l e c u l a r Weight Apparatus made by Perkin-Elmer ( H i t a c h i ) ; t h e
e s s e n t i a l f e a t u r e s o f t h e apparatus
diagram 3.2.
a r e presented
schematically i n
The d e t e r m i n a t i o n o f m o l e c u l a r w e i g h t depends on t h e d i f f e r e n c e
i n vapour p r e s s u r e between a drop o f pure s o l v e n t and a d r o p o f a
solution
( o f t h e m a t e r i a l under i n v e s t i g a t i o n )
i n t h e same s o l v e n t ;
such d i f f e r e n c e s a r e n o t e a s i l y measured d i r e c t l y .
In p r a c t i c e
two c l o s e l y matched t h e r m i s t o r s each capable o f h o l d i n g a d r o p o f
s o l v e n t o r s o l u t i o n a r e placed i n a t h e r m o s t a t e d c o n t a i n e r i n which
a pool o f pure s o l v e n t I s m a i n t a i n e d I n e q u i l i b r i u m w i t h I t s s a t u r a t e d
vapour.
Each t h e r m i s t o r i s p a r t o f a Wheatstone B r i d g e .
A drop o f
pure s o l v e n t i s p l a c e d on one t h e r m i s t o r and a drop o f s o l u t i o n on t h e
o t h e r , t h e r a t e o f e v a p o r a t i o n and c o n d e n s a t i o n w i l l
the
d i f f e r between
two t h e r m i s t o r s c o n s e q u e n t l y s e t t i n g up a t e m p e r a t u r e
differential.
The r e s u l t i n g o u t o f balance p o t e n t i a l o f the b r i d g e can be measured
w i t h c o n s i d e r a b l e accuracy and when t h e system
Is calibrated with
m a t e r i a l o f known m o l e c u l a r w e i g h t t h e m o l a l c o n c e n t r a t i o n o f t h e
unknown s o l u t i o n can be o b t a i n e d and hence t h e m o l e c u l a r w e i g h t o f
the
solution.
SOLUTION
DROP
SATURATED
, S O L V E N T VAPOR
SOLVENT
DROP
"I
D.C. W H E A T S T O N E
BRIDGE
METER
TO
REFERENCE
THEHMISTOR
TO SAMPLE
THERMISTOR
S O L V E N T L I Q U I D PHASE
Diagram 3.2
E s s e n t i a l F e a t u r e s o f Model 115 M o l e c u l a r Weight Apparatus
b)
The
Determinations
The
I n s t r u m e n t was
and c h l o r o f o r m as t h e s o l v e n t .
c a l i b r a t e d u s i n g b e n z l l as t h e s t a n d a r d
The
I n s t r u m e n t c o n s t a n t K, which
t h e s l o p e o f t h e graph r e p r e s e n t i n g t h e o u t o f b a l a n c e p o t e n t i a l
measured In a r b i t r a r y u n i t s p l o t t e d a g a i n s t t h e m o l a l
(AR)
concentration.
The c o n s t a n t used I n t h e s e p a r t i c u l a r d e t e r m i n a t i o n s was
The m o l e c u l a r w e i g h t o f t h e p r o d u c t f r o m Experiment
Is
51273*
1 was
o b t a i n e d by
measuring t h e o u t o f balance p o t e n t i a l f o r s e v e r a l s o l u t i o n s o f
d i f f e r e n t c o n c e n t r a t i o n and e x t r a p o l a t i n g t o z e r o c o n c e n t r a t i o n u s i n g
a l e a s t squares p r o c e d u r e .
K
I s t h e n g i v e n by t h e e x p r e s s i o n
=K
1Im A R
C->0
/
and f o r t h i s sample was
/r
L
5080.
Before the values of M„for the products from the s i x pyrex
(Experiment 2) were d e t e r m i n e d ,
r e - c a l i b r a t e d g i v i n g an
"the I n s t r u m e n t was
i n s t r u m e n t c o n s t a n t o f 56292.
cleaned
The
tubes
and
molecular
w e i g h t s determined f o r t h e s i x p r o d u c t s a r e t a b u l a t e d below, t o g e t h e r
w i t h t h e c o r r e l a t i o n c o e f f i c i e n t s f o r t h e l e a s t squares f i t o f t h e
extrapolated
line.
Isopropanol:Benzene R a t i o
mis
1:14
1:9
1:5
1:4
1:2
1:1
It
Correlation
Coefficient
0.700
0.878
0.999
-
0.@65
0.931
D.P.
14.8
15
14.1
16.5
9.7
7.7
4280
4310
4060
4750
2800
2230
i s c l e a r f r o m t h e t a b l e t h a t as t h e c o n c e n t r a t i o n o f
isopropanol decreases t h e m o l e c u l a r w e i g h t o f t h e p r o d u c t
increases and then reaches a p l a t e a u v a l u e , t h i s t r e n d
e a s i l y seen i n g r a p h i c a l f o r m I n F i g u r e 3.3.
initially
I s more
There a r e a number o f
CO
c
a
CD oC
CL
O
CO
OO
CD
CD
CD
l±J
ID
C/)
C3
oo 2
o o o o
ID
o CO
12:
f a c t o r s which may c o n t r o l t h e m o l e c u l a r w e i g h t a t t a i n e d and many
o f these were d i s c u s s e d I n S e c t i o n 2.k\
however, I t seems p r o b a b l e
t h a t t h e lower m o l e c u l a r w e i g h t s o f t h e p r o d u c t s which
from the solutions
precipitated
having h i g h e r I s o p r o p a n o l c o n c e n t r a t i o n s r e s u l t
s i m p l y f r o m t h e i r b e i n g removed f r o m s o l u t i o n b e f o r e c o m p l e t i n g
reaction,
t h a t Is a simple s o l u b i l i t y e f f e c t c o n t r o l s t h e
attained.
On t h e o t h e r hand, t h e f a c t t h a t t h e p o l y m e r i z a t i o n
tends- t o a l i m i t i n g m o l e c u l a r w e i g h t o f c a . 4350 ( i e a D.P. ^ 1 5 )
may be a r e s u l t o f t h e r a t i o o f In-cage c h a i n t e r m i n a t i n g r e a c t i o n s
t o out-of-cage chain extending reactions;
t h i s r a t i o may be
a f f e c t e d by aspects o f monomer and s o l u t i o n s t r u c t u r e and may w e l l
v a r y f r o m system t o system.
In t h e l i m i t e d time a v a i l a b l e t o t h e
a u t h o r i t was decided n o t t o pursue t h i s m a t t e r f u r t h e r b u t t o
examine t h e subsequent steps o u t l i n e d I n S e c t i o n 2.5.
PART 3-
REACTIONS OF P0LYBENZ0PINAC0L I J J a
The t h r e e intended s t e p s t o polymers TfTT and/or 237" have a l r e a d y
been d i s c u s s e d I n S e c t i o n 2.5 and f o r t h e purpose o f I n v e s t i g a t i n g
t h i s proposed
sequence o f r e a c t i o n s 12.83 grms o f p o l y b e n z o p i n a c o l
I H a was prepared by I r r a d i a t i o n o f m-di benzoyl benzene i n a 15:1
solution.
The I n f r a r e d s p e c t r n ^ o f t h i s s t a r t i n g m a t e r i a l
Is
recorded I n Appendix A, No.133.7
The D e h y d r a t i o n o f Polybenzopinacol
The p i h a c o i - p i n a c o i o n e rearrangement
(ETJa)
i s a well
known
reaction;
f o r t h e model system, benzopinacol t o b e n z o p i n a c o l o n e , t h e r e a c t i o n I s
quantitative.
In I n i t i a l
experiments w i t h Polymer U J a
Iodine i n
a c e t i c a c i d and d i m e t h y l s u l p h o x i d e were t r i e d as c a t a l y s t s s i n c e t h e y
were known t o be e f f e c t i v e f o r t h e model compound r e a c t i o n .
Experiment
1
Polybenzoplnacol
( H I a - 1 grm) was r e f l u x e d
a m i x t u r e o f benzene (2k m i s ) , g l a c i a l a c e t i c a c i d
crystal.
In
(25 mis) and an l o d i
Only a f t e r 20 hours r e f l u x l n g d i d t h e r e a c t i o n go t o
c o m p l e t i o n as j u d g e d by I n f r a r e d s p e c t r o s c o p y
(Appendix A; No.15).
A molecular weight determination on t h e product I s o l a t e d from t h i s
r e a c t i o n showed t h a t d e g r a d a t i o n had t a k e n p l a c e ( S ^ = 706, D.P. =
2.4)
T . l . c . I n d i c a t e d t h e presence o f one component o n l y .
Experiment 2
1:1
Polybenzopinacol
(TTTa - 1 grm) was r e f l u x e d
(v/v) m i x t u r e o f D.M.S.O. and benzene f o r s e v e r a l hours
which no r e a c t i o n had t a k e n p l a c e as j u d g e d by i n f r a r e d
(Appendix A; No. \k).
D.M.S.O. which was
in a
after
spectroscopy
The spectrw»»shows t h e presence o f o c c l u d e d
v e r y d i f f i c u l t t o remove d e s p i t e prolonged pumping
on t h e vacuum l i n e .
H I g g l n s and coworkers worked on t h e p o l y b e n z o p i n a c o l s r e s u l t i n g
f r o m p h o t o c o n d e n s a t i o n o f p, p ' - d I b e n z o y l d f p h e n y l e t h e r , p,p'-dI benzo y l diphenylmethane and p , p ' - d I b e n z o y l - 1 , 2 - d i p h e n y l e t h a n e and
achieved t h e d e s i r e d d e h y d r a t i o n u s i n g s u l p h u r i c a c i d - d i o x a n e s o l u t i o n s
T h e i r a n a l y s i s suggested t h a t t h e rearrangement
place ( I . e .
expected d i d n o t t a k e
m i g r a t i o n o f a phenyl group) b u t I n s t e a d c h a i n m i g r a t i o n
t o o k p l a c e , t h u s t h e i r a n a l y s t s p r e d i c t s s t r u c t u r e XL r a t h e r t h a n X
(see 2.5 Stage 2 ) .
Experiment 3
stirred solution
Polybenzopinacol
( a t room t e m p e r a t u r e ) o f cone. h^SO^ (25 mis) and
1,4 d i o x a n (150 m i s ) , which was
i e f t s t i r r i n g f o r 16 h o u r s .
r e s u l t i n g dark-brown s o l u t i o n was
for
( i l i a - 5 grms) was added t o a
t h e n added t o Iced w a t e r ,
s e v e r a l m i n u t e s , and t h e n f i l t e r e d .
The s o l i d was
i n T.H.F. and s l o w l y added t o a l a r g e volume o f w a t e r
The
stirred
redissolved
(ca. 2 l i t r e s ) .
The p r o d u c t d i d n o t p r e c i p i t a t e , as expected by analogy w i t h H i g g i n s '
work, b u t formed an e m u l s i o n .
T h i s e m u l s i o n c o u l d o n l y be broken by
a d d i n g l a r g e q u a n t i t i e s o f d i l u t e HC1
formed.
The
p r e c i p i t a t e was
a f t e r which a p r e c i p i t a t e
recovered by f i l t r a t i o n , washed w i t h
Na^CO^ s o l u t i o n , t h e n w a t e r , and e v e n t u a l l y d r i e d on t h e vacuum
line.
The
I n f r a r e d spectrum o f t h i s p r o d u c t
(Appendix A; No.16)
I n d i c a t e d complete consumption o f OH f u n c t i o n and f o r m a t i o n o f an
i n t e n s e c a r b o n y l a t I675 cm"', c o n s i s t e n t w i t h t h e f o r m a t i o n o f
e i t h e r X o r XT.
apparatus was
At t h i s stage I n t h e work t h e m o l e c u l a r w e i g h t
not f u n c t i o n i n g and so i t was
not p o s s i b l e t o d e t e r m i n e
I f t h e d e h y d r a t i o n had been accompanied by d e g r a d a t i o n as i n
Experiment
1; however, t h e avoidance o f h i g h temperatures
in this
l a s t procedure g i v e s cause f o r o p t i m i s m t h a t I t o c c u r r e d w i t h o u t
degradation.
3.8
Reduction o f Polymer X and/or X I
The a t t e m p t e d r e d u c t i o n w i t h sodium b o r o h y d r l d e o f a t o l u e n e
s o l u t i o n o f t h e p r o d u c t Experiment
3, S e c t i o n 3-7 was
u n s u c c e s s f u l as j u d g e d by t h e I n f r a r e d spectrum o f t h e
p r o d u c t (Appendix A; No.17).
totally
Isolated
Repetition of the reaction using
dloxane
as s o l v e n t r e s u l t e d i n a p r o d u c t i n w h i c h t h e c a r b o n y l f u n c t i o n a t
I675 cm ' I n t h e I n f r a r e d spectrum
(Appendix A; No.
18) was
almost
-
c o m p l e t e l y consumed and r e p l a c e d by a broad band a t 3220 cm '
assigned t o h y d r o x y l ; t h i s r e s u l t b e i n g c o n s i s t e n t w i t h t h e f o r m a t i o n
of
3.9
polymers 211
and/or fit 11 (see S e c t i o n 2 . 5 ) •
D e h y d r a t i o n o f Polymers 211 and/or XEEL
in o r d e r t o t r y and complete
the
t h e sequence o f proposed r e a c t i o n s
p r o d u c t o b t a i n e d as d e s c r i b e d i n t h e p r e v i o u s s e c t i o n was
i n a m i x t u r e o f a c e t i c a c i d , benzene and
Iodine.
A f t e r t h e usual
I s o l a t i o n and d r y i n g procedure a p r o d u c t was o b t a i n e d , t h e
spectrum o f which
I s shown I n Appendix A; No.19.
refluxed
infrared
I f e v e r y t h i n g had
gone a c c o r d i n g t o p l a n t h i s p r o d u c t s h o u l d have been e i t h e r X T J T and/or XT.
51
T h i s r e s u l t poses i m p o r t a n t q u e s t i o n s ; namely i s i t j u s t t h e
l a s t stage o f t h e sequence which has f a i l e d t o go a c c o r d i n g t o p l a n ,
o r was t h e s t a r t i n g m a t e r i a l f o r t h e l a s t s t a g e n o t as o r i g i n a l l y
assumed.
I t I s p o s s i b l e t h a t t h e c a r b o n y l a b s o r b t l o n s observed I n
spectrum 19 r e s u l t s f r o m t h e p r o d u c t
h y d r o x y l s present
o f esterlfIcation o f the
i n t h e s t a r t i n g m a t e r i a l ; a c e t a t e c a r b o n y l would
be c o n s i s t e n t w i t h t h e band a t 1750 cm
1675
The s t r o n g band a t
cm ' might be a s c r i b e d t o an a c e t y l a t ton p r o d u c t o f t h e
a r o m a t i c r i n g s , acetophenone c a r b o n y l absorbs a t ca 1685 cm"',
a l t h o u g h t h i s e x p l a n a t i o n seems somewhat u n l i k e l y .
C l e a r l y t h i s f i n a l r e s u l t r a i s e s q u e s t i o n s which can o n l y be
answered by f u r t h e r experiment,
restricted
PART k.
The
u n f o r t u n a t e l y the author's
time d i d n o t a l l o w these e x p e r i m e n t s
t o be c a r r i e d o u t .
CONCLUSIONS AND SUGGESTIONS FOR FURTHER WORK
investigation o f the photoreductive polymerization of
m-dibenzoyl benzene demonstrates some o f t h e d i f f i c u l t i e s w h i c h can
be encountered
I n syntheses o f t h i s t y p e .
A l t h o u g h i t may be
p o s s i b l e t o improve on t h e m o l e c u l a r w e i g h t s o b t a i n e d f o r polymer TTTa
In t h i s work by m a n i p u l a t i o n o f r e a c t i o n c o n d i t i o n s t h e r e s u l t s
r e p o r t e d here suggest t h a t such Improvements a r e l i k e l y t o be s m a l l .
OH OH
Ph Ph
TTTa
The f a c t o r s l i m i t i n g t h e a t t a i n a b l e m o l e c u l a r w e i g h t a r e n o t
c o m p l e t e l y c l e a r b u t a r e p r o b a b l y complex; on t h e one hand
simple
s o l u b i l i t y o f monomers has been d e m o n s t r a t e d t o be i m p o r t a n t and
on t h e o t h e r i t may be f a c t o r s such as s t e r i c h i n d r a n c e o f t h e g r o w i n g
chain and the way
i n which
i t I s c o l l e d and/or s o l v a t e d .
A p r e l i m i n a r y e x a m i n a t i o n of t h e proposed
u s i n g polymer
out
EEIa as s t a r t i n g m a t e r i a l was
I n t h e t i m e a v a i l a b l e to t h e a u t h o r .
these r e s u l t s t h e f i r s t
sequence o f r e a c t i o n s
a l l t h a t c o u l d be c a r r i e d
However, on t h e b a s i s of
two s t e p s appear to proceed as
expected
a l t h o u g h t h e s i n g l e a t t e m p t a t t h e t h i r d s t a g e was u n s u c c e s s f u l .
I f t h i s p r o j e c t I s I n v e s t i g a t e d f u r t h e r I t would seem a p p r o p r i a t e
to examine t h e s y n t h e t i c scheme proposed
i n S e c t i o n 2.5
I n more d e t a i l
b e f o r e spending f u r t h e r t i m e on a t t e m p t i n g to o b t a i n h i g h e r m o l e c u l a r
w e i g h t samples of t h e s t a r t i n g m a t e r i a l , polymer
In t h e I n i t i a l
stages of any c o n t i n u a t i o n ,
TJIa.
i n v e s t i g a t i o n by means
of c o n v e n t i o n a l t e c h n i q u e s such as m o l e c u l a r w e i g h t measurements and
'H n.m.r. s p e c t r o s c o p y would seem to be t h e o b v i o u s f i r s t s t e p ;
u n f o r t u n a t e l y I n t h e l a t t e r stages of t h e p r e s e n t a u t h o r ' s work t h e s e
t e c h n i q u e s were n o t a v a i l a b l e .
I f t h e programme was
the
b r o u g h t to a s a t i s f a c o r y s y n t h e t i c c o n c l u s i o n
problem of d i s t i n g u i s h i n g between I s o m e r i c s t r u c t u r e s of t h e
p o s s i b l e p r o d u c t s remains.
Here a g a i n , however, s i m p l e t e c h n i q u e s
may w e l l be a b l e to p r o v i d e d e f i n i t i v e answers; f o r example on
o z o n o l y s i s polymer A l i i , s h o u l d t h e o r e t i c a l l y be degraded c o m p l e t e l y
to
m- d|benzoylbenz?ne, whereas t h e I s o m e r i c polymer 2 1 s h o u l d y i e l d
benzophenone and a p o l y m e r i c k e t o n e .
APPENDIX A
Vacuum System
V o l a t i l e compounds were handled I n a c o n v e n t i o n a l vacuum
system I n c o r p o r a t i n g
I n f r a r e d Spectra
557 G r a t i n g
a mercury d i f f u s i o n pump and r o t a r y o i l
pump.
were recorded w i t h b o t h a P e r k i n - E l m e r k57 and
Infrared
U l t r a v i o l e t Spectra
Spectrophotometer.
were recorded w i t h a Unlearn SP800
spectrophotometer.
Carbon and Hydrogen A n a l y s i s
2*40 CHN A n a l y s e r .
were c a r r i e d o u t w i t h a P e r k l n - E l m e r
APPENDIX B
INFRARED SPECTRA
5^.
INDEX TO INFRARED SPECTRA
Spectrum No.
Compound (where known)
1
m-dibenzoylbenzene
2
m-blsbenzhydrol
3
p-bisbenzhydrol
Reference t o Diagram
or Script
(a)
- Diagram
-
k
-
3.5
5
-
3.5
" ) a)
6
-
3.5
M ) a)
3.5
" ) b)
7
8
9
10
11
12
13
\k
15
polybenzopinacol
"
( d e r i v e d f r o m merrygo-round r e a c t i o n s )
-
0
3.5
III)
3.5
iii)
3.5
lii)
3.6
i ) Experiment 1
3.6
I) Experiment 2
Part 3
Introduction
3.7
Experiment 2
3.7
Experiment 1
Experiment 2
16
X and/or XI
3.7
17
X I I and/or X I I I
3.8
18
X I I and/or X I I I
3.8
19
XIV and/or XV
3.9
55.
X)
40
50
60
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sir.Tion
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424.
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