10.569 Synthesis of Polymers
Prof. Paula Hammond
Lecture 28: Introduction to Polymer Functionalization: Motivations, Yield,
Crystallinity, Solubility Issues, Common Functionalization Approaches
Polymer Functionalization
Can make a polymer with desired side group R via
- direct route
H2C
H
H
CH
C
C
R
H
R
n
- or perform reaction on existing polymer H
a)
CH
H2C
CH2
X
n
X
H
reagent
b)
C
CH2
C
n
R
Issues with reactions on polymers
Reactions on Polymers vs Reactions on Small Molecules
Small Molecule
X
Y
X
Y
X
Y
X
react to form
Y
Y
X
Polymer Chain
X
X
X
X
X
+
Y
X
X
Y
nY
1. Yield has different meaning
Small molecules: 80% yield
pre-product 80%
spin process
unreacted molecule
+ reagent 20%
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.
Polymer chain: 80% yield →
no separation to
“pure” component
80
Y
20
form copolymer with 80%
functionalized groups
X
2. Localized concentration effects
(e.g. high MW polymer in intermediate solvents)
Rx
polymer chains may “hide”
access of reagent
Rx
Rx
very large solvent effects
3. Polymer morphology
(e.g. semicrystalline polymers)
Functionalized/etched away
on surface
small
crystallites
→ can be relatively impermeable to solvent + reagent
Block copolymers in selective solvent
solvophobic block
is less accessible
to reaction
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
can be advantageous
for selective modification
of blocks
Lecture 28
Page 2 of 7
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.
Selective Hydrogenation
e.g.
H2
Pt
PB
PE
rubber
CH2
n
waxy crystalline solid
CH2 CH
CH2 CH
polyV-cyclohexane
poly 1,4 cis polyisoprene
(rubbery low Tg)
CH3
CH3
PI
PEP
limit crystallinity
4. Sterics are amplified
Steric hindrance can reduce reactivity of neighboring units
H
CH2 C
+
H
CH2 C
R I
N
N
reactive and can
undergo substitutions
I
polyvinyl pyridine
PVP
R = C4H9 is 4x faster reaction rate than
R = C18H37
+
But rates are the same for
R I
N
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Lecture 28
Page 3 of 7
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.
Note: sterics can often be alleviated with alkyl or ethylene oxide
e.g.
I
R
vs
Y
Y
easier, faster
rate
Y
Y
Y
Y
5. Electrostatics can play a role in reaction rate
RI
N
N
N
N
N
I R
N
R
I
lowered reactivity
by factor of 3
due to charge repulsion
- unfavorable to make a new N+ group here b/c of neighboring +s
- by saturating with salt (e.g. NaCl) helps reduce distance between
+
and - charge
Debye length
∴ more able to react
s close to each other
N
Consider Kinetics
AAAAAAAA
AAABABAAA
k2
ko
AAABAAAAA
k1
vs.
if ko = k1 = k2
Bernoullian distribution of
functionalization
different reactivity than previous with 2A partners
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Lecture 28
Page 4 of 7
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.
e.g. for highly reactive systems
CH3
CH2 C
C
CH3
SOCl2
CH2 C
O
O
C
S
O
Cl
H
O
Cl
Cl
auto-acceleration (a.k.a. autocatalytic effects)
e.g. hydrolysis of PMMA
CH3
CH2
CH3
CH2
C
CH3
C
C
O
O
HO
CH2
C
C
O
O
O
O
CH3
C
(treat with
strong base)
CH3
CH3
HO
k2
O C
H3C
O O
O C
C O C O
C
O
O
H3C
CH3
O
C O C O C O
O
O
O
CH3
k2 > k1 ⇒ autocatalysis
Common Polymer Functionalization
Make polymers that are otherwise inaccessible
1. Polyvinyl alcohol (PVA)
CH2
H
C
OH
O
CH2 CH
isomerizes
OH
not stable!!
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
CH3 CH
stable form
Lecture 28
Page 5 of 7
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.
Polyvinyl Acetate
OH
hydrolysis
free radical
CH2 CH
CH2 CH
or cationic
O
C
CH2 CH
∴ cannot polymerize
CH2 CH
(acid or base)
O
O
OH
C
CH3
O
O
+
CH3
CH3 C
OH
Polyvinyl acetyls are made from PVOH
O
CH2
R CH
CH2 CH
-H2O
+ aldehyde
OH
CH2 CH
O
CH
CH
O
R
Also
CH2
CH2
H
N
Linear polyethylene imine
H
N
N
N
H
aziridine
H2N
Instead use 2-ethyl-2-oxazoline
(EOX)
2. Halogentation of vinyl polymers
- improves water resistance
- improves fire/flame stability (chlorination and some case 1 bromination)
chlorination of natural rubber
Hydrochlorination
HCl
CH3
CH2
C
CH
CH3
H
CH2
CH2
C
CH2
CH2
CH3
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
CH2
C
Cl
CH2
CH2
Cl
Lecture 28
Page 6 of 7
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.
Plain chlorination
Gives more Cl
CH3 Cl
Cl2
CH2
C
C
Cl
H
CH2
Can add more Cl by free radical
→ aromatic substitutions next time
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Lecture 28
Page 7 of 7
Citation: Professor Paula Hammond, 10.569 Synthesis of Polymers Fall 2006 materials, MIT
OpenCourseWare (http://ocw.mit.edu/index.html), Massachusetts Institute of Technology, Date.