Macromolecular Chemistry
Mn 
 MiNi
 Ni
Lecture 6
Mw 
WiMi
Wi

2
NiMi

 NiMi
Mw
PI 
Mn
Chemistry 367L/392N
Molecular Weight
Distribution in Polymeric
Materials
Molecular weight
Chemistry 367L/392N
Radical Chain Growth Polymerization

Among the initiators used for radical chain-growth
polymerization are diacyl peroxides, which
decompose as shown on mild heating
O
O
O

O
Dibenzoyl
peroxide
O
2
A benzoyloxy
radical
O
2
+ 2 CO 2
A phenyl
radical
Chemistry 367L/392N
Initiation
H2C
CH
CH2
CH
Chemistry 367L/392N
Propagation
CH2
CH
H2C
CH
CH2
CH
H2
C
CH
Chemistry 367L/392N
Termination
Coupling
Ph*
n Ph*
n
R
2 Ph*
R
R
R
n
R
R
2 Ph*
+
n
R
R
n Ph
H3C
R
Disproportionation
Chemistry 367L/392N
Radical Generation

Thermolysis
R• + N2 + • R'
R N N + • R'
R N N R'
Thermal decomposition of azo-compounds
CN
NC
N
N
N
CN
2,2’-azobis(2-methylpropanenitrile)
(AIBN)
N
CN
1,1’-azobis(1-cyclohexanenitrile)
Chemistry 367L/392N
Thermolysis of peroxides -O-OR O O R'
R O
R' O
+
Thermal decomposition of peroxides
O
O
O
O
O
O
Benzoylperoxide (BPO)
di-tert-butylperoxide
+
Na O O
S
O
O
O
O
S
+
O O Na
sodium persulfate
Chemistry 367L/392N
Photolysis
R
O
O
R'
R
h
C
O
O
C
+
R'
Photolysis of benzoin (R=R’=H).
Chemistry 367L/392N
Redox Initiators
O
O
+
H
Fe
2+
O
+
Fe
3+
+
_
OH
+
Fe(III)
Redox decomposition of cumyl hydroperoxide
-O S
3
O
O
S3O -
+
Fe(II)
SO4
--
+
SO4*-
Redox decomposition of persulfate
Chemistry 367L/392N
Self initiation of monomer
+
H
Diels-Alder
dimerization
[1,3]-H shift
molecular-assisted
homolysis
Alder ene-reaction
Chemistry 367L/392N
d[I ]
kd  dt
kd
→ 2 R·
I
-E/kT
e
k = kmax
[I]
t 
1/ 2
[Time]
ln 2
k
= 0.693/kd
d
For efficient polymerization rate - need sufficient radicals.
Too few - slow, poor conversion with t
Too many - exothermic, low mol. wt
AIBN
64
82
100
120
10 hrs
1 hr
6 mins
1 min
Optimum = 75-90 o C --> Reaction Time ~ 2-3 (t 1/2 )
Chemistry 367L/392N
Decomposition of Thermal Initiator
kd
→ 2 R·
I
Efficiency factor ( f ):
CN
O
O
O
N
N
O
CN
di-tert-butylperoxide
f = 0.65
R 
i
dt
O
O
O
AIBN
f = 0.75
d [ R •]
O
di-tert-butylperoxalate
f=0.95
 2 f k [ I]
d
Chemistry 367L/392N
Temperature of 1 hr t1/2
Chemistry 367L/392N
Kinetics of free radical polymerization
 Steady state assumption:
Ri = Rt
- d[M·]
Ri=
= 2 kt [M·]2 Where kt = ktc+ ktd
dt
fk d [ I ]
2 fk [ I ]  2 k [ M ] 2
So…
d
[M·]=
t
kt
What is the Propagation rate ( Rp )
-d[M]
= kp[M][M·]
Rp=
dt
-d[M]
= kp[M]
Rp=
dt
fkd[ I ]
kt
Chemistry 367L/392N
Kinetics of free radical polymerization
Average kinetic chain length ( Ӯ )
Rp Rp

Ӯ 
Ri Rt
k p [M ]
k p[M ]
[ M ][ M ]

2
ӮKp
2
2 kt [ M ]
2kt [ M ]
( fktkd[ I ]
Disproportionation : DP = Ӯ
Combination :
DP = 2Ӯ
Chemistry 367L/392N
Arthur K. Doolittle Award
The Arthur K. Doolittle Award, established by the Union
Carbide Corporation, is given to the authors of an outstanding
paper presented before the PMSE Division at each national
meeting of the ACS. A prize in the amount of $1,000.00 is
financed with the gift of royalties from A. K. Doolittle's book,
Technology of Solvents and Plasticizers. All papers are
evaluated on the basis of content, with emphasis on
originality and development of new concepts, and on the
quality of presentation. Recipients are selected by an
anonymous panel of judges appointed by the Chairman of the
Doolittle Award Committee.
Chemistry 367L/392N
TEMPO Controlled Polymerization
1993 M. K. Georges, R. P. N. Veregin, P. M. Kazmaier and G. K. Hamer (Xerox
Corporation), "Narrow Molecular Weight Resin by Free Radical Process."
I
I
O
+
O
N
N
(2,2,6,6-tetramethylpiperidinyl-1-oxy)
TEMPO
Monomer
Polymer
Polymer
+
O
O
N
N
DP =
[monomer]
[Initiator]
Chemistry 367L/392N
Controlled Free Radical
Polymerization
Chemistry 367L/392N
Control of polymer Architecture
O
O
O
N
O
+
O
CH3
AIBN
O
O
O
O
OCH3
OTEMPO
O
OCH3
O
OCH3
O
OTEMPO
Chemistry 367L/392N
O
O
O
OCH3
O
O
OCH3
O
OCH3
O
OTEMPO
OTEMPO
O
O
O
O
OCH3
O
OCH3
O
OCH3
O
Ph
Ph
Ph
Ph
Chemistry 367L/392N