10.569 Synthesis of Polymers
Prof. Paula Hammond
Lecture 33: Ring-Opening Metathesis Polymerization, Oxidative Coupling,
Electrochemical Polymerization, Case Study: Electro-Active Polymers
SFRP
- Useful for modifying surfaces
- Generation of high adhesive surfaces
Mechanism of Olefin Metathesis (exchange double bonds)
Transalkylation
R
CH
CHR'
RCH
CHR
+
R
CH
CHR
R'CH
CHR'
Transalkylidenation
R'CH
CHR
R'CH
CHR'
+
RCH
CHR'
RCH
Actual
Rate
CHR
The double bonds exchange
Cyclic Alkene
n
+
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.
Ring Opening Metathesis Polymerization (ROMP)
Catalytic Process ⇒ Efficacy of process is dependent on catalyst
Polymer is also dependent on monomer structure
Potential monomers
1. C=C must be in a strained ring system
ROMP
(no strain)
ROMP
100% conversion
far from equilibrium
ROMP
100% conversion
ROMP
[M]eq
cyclooctane
cyclobutane
cyclopentane
(not as strained)
Mono, Bi and Tricyclic ROMP Monomers
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Lecture 33
Page 2 of 10
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.
n
n
n
n
tricyclic
m
Reactivity of Bi and Tricyclic >> Monocyclic
O
O
CF3
CF3
O
CO2Me
CO2Me
A
C
B
Examples of Norbornadienes
oxygen at bridge pinnacle
2. For typical monocyclic alkenes:
Substituents available are limited
O
R
R ≠ NH2,
C OH , -OR’ ,
OH
Must use something less reactive.
3. Can’t polymerize cyclic alkene with R-substituent directly on C=C bond.
Won’t undergo ROMP.
CH3
Whereas
CH3
will undergo ROMP.
For bicyclics, (and tricyclics)
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Lecture 33
Page 3 of 10
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.
→
→
→
→
much faster rxn rates
always get 100% conversion due to high ring strain
less prone to secondary rearrangements of backbone (shuffling)
side reactions with catalyst are minimized
∴ can introduce some polar substituents
ex
CF3
Cl
AcOH2C
F
CH2OAc
Schrock catalysts: W, Mo
(MIT)
Grubbs catalyst: Ru
(CalTech)
Norbornene will polymerize in its
functionalized forms → functionalized polymers
n
n
R
R
O
AcOH2C
AcOH2C
n
AcOH2C
CH2OAc
End-Capping Living ROMP – Wittig Reaction
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Lecture 33
Page 4 of 10
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.
Aldehyde
Schrock Initiator
+
[Mo]
X
CHO
n
[Mo] = Mo(NAr)(O-t-Bu)2
X
+ [Mo]=O
n
+
[Mo]
n
CHO
+
[Mo]=O
n
Living ROMP
Ri very rapid with specific catalyst
∼ tolerant catalysts for functional groups
→ very low PDI → 1.03 – 1.05
“perfect polymers” almost nature-like
O
H
X C H
+
Mo
C
X
desired
H
end
C
group
X
O
Conducting Polymers
Conjugated polymers that allow e- transfer along chain.
Polyacetylene
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Lecture 33
Page 5 of 10
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.
C
C
C
C
C
chains should be
oriented macroscopically
C
eπ-orbitals overlapping
→ huge delocalization of ee- can move back and forth on polymer chain ⇒ conjugation
⇒ conjugation
polyacetylene from HC≡CH (gas)
slightly explosive
1st record of polyacetylene → 2-N type polym.
(gas bubbled through solvent with solid phase catalyst)
⇒ powder ⇒ intractable (Tm too high insoluble)
James Feast
monomer
F3C
W/Sn
n
W/Al
F3C
F3C
CF3
CF3
heat
+
n
CF3
Durham Route
Synthesis of Diblocks
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Lecture 33
Page 6 of 10
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.
+
Ln[W]
Ln[W]
n eq.
n
norbornene
catalyst
+
Ln[W]
m eq.
n
R
R
feast monomer
Ln[W]
m
R
n
R
O
R'
Ln[W]
O
+
H
R'
m
R
+
R
R'
m
R
n
n
R
TriBlock Copolymers Containing Durham Polyacteylene
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Lecture 33
Page 7 of 10
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.
+ 100
N
or
[Mo]
100
Mo
LH
O
[Mo]
100
+ 100 F3C
100
F3C
LD
F3C
CF 3
+ 0.5
or
O
O
O
conjugated
aldehyde
for Wittig
O
100
F3C
100
100
100
F3C
CF 3
CF 3
100o, 30 min
-200
CF3
CF3
100
100
100
100
Shirakawa: coated walls of Schlank tube with catalyst, then admitted
acetylene gas
⇒ form a thin film on glass walls
silver, brittle, insoluble, intractable
⇒ confirmed e- conductivity
∼ 0.1 S/cm – 1 S/cm
Difficult to isolate acetylene
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Lecture 33
Page 8 of 10
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.
Conjugated Polymers (common)
Heeger and MacDiarmid
Pyrrole
N
H
N
n
H
polypyrole
Aniline
NH2
N
H
polyaniline
N
H
x
y
Thiophene
polythiophene
S
S
favorable properties in terms of stability
can be functionalized
n
Oxidation and Reduction Approaches to Polymerization
- Electrochemical
- Chemical (introduction of a reagent)
cathode
anode
1. Reduction at cathode
R
electrolyte
C CH2
R
+ e-
C CH2
H
H
radical anion
2. Oxidation at anode
R'
C CH2
H
- e-
R
C CH2
H
radical cation
Generate combination
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
Lecture 33
Page 9 of 10
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.
Often radicals combine to generate dionic species.
Electropolymerization of Pyrrole
Initiation
+.
N
N
H
H
+ e-
Propagation
+.
2
+
N
H
H H
N
H
N
N
N
H H
H
+.
H
N
+
N
H
x
+.
H
+ 2H+
+.
N
N
N
+ 2H+
H
H
+ ex+1
Termination
H
+.
N
H
H2O
N
N
O
H
N
H
x
10.569, Synthesis of Polymers, Fall 2006
Prof. Paula Hammond
x
Lecture 33
Page 10 of 10
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.