中科大聚合反应原理专论课件-Chapter 2 - Controlled Free Radical Polymerization

COOCH3
CN
. CH3
CH3 C (MMA)n-1MMA COOCH3 +St
.Ph
+ C Ph CN
CH3
Ph
CH3 C (MMA)n (St)m C Ph
COOCH3
CN
b. B-O·radical
• Borinate radical can be produced by heating, for example:
• C(R2)3 should be stable radicals, • Can exist in high concentration.
• Stable during the polymerization, no substitution reaction, or dehydrogenation,
. . Ph N=N CPh3 heat Ph + CPh3
. . Ph + CH2=CH
Ph CH2 CH
Propagation
. . Ph (CH2 CH )n CH2 CH + CH2=CH Ph (CH2 CH )n+1CH2CH . . Ph (CH2 CH )n CH2 CH + CPh3 Ph (CH2 CH )n CH2 CH CPh3
is possible.
§2-2 Difference between anionic and free radical polymerization
Table 2-1. Comparison of free radical with living anionic polymerization
Active Species
method of free radical polymerization
Process conditions: bulk, solution, suspension, emulsion polymerizations.
Medium: water and common organic compounds
Some side reactions
Benzene Ph N=N CPh3 heat
N2 + Ph. + Ph3C.
Ph. +
Ph .
H 1
1 + Ph3C.
Ph
H 2
H CPh3
Ph . + Ph3C.
H
Ph3CH + Ph
Another compounds as initiator
C
Radical polymerization of MMA, St, and MA
for example,
. . Ph3 C + Ph3 C
Ph3C H
Thus azo compounds were synthesized
Ph N N CPh3
Initiation reaction
Ph N N CPh3
Ph
CH2 CH
Ph N2 CPh3 Ph CH2 CH
Initiation and polymerization mechanism
Initiation
CC
CPh3
CPh3
• Triphenyl methyl radicals are very stable and
can exist in high concentration
• Fast equilibrium, reduce the concentration of chain radicals
Chapter 2
Controlled Free Radical Polymerization
§2-1 The significances of living free radical polymerization
1. Importance in polymer industry
(1) Most of polymer materials are produced by the
(1) The compounds with triphenyl methyl group
CC C
Ph3CCH2CH2CH2OH N N CPh3
Theoretical consideration
• Homolytical split of C-C bond in polymerization condition
Preparation of block copolymers Comparing two radicals
.N N N
a
.N N N
b
Radical stability b >> a
4. Design of initiator
• The component of initiator: R1-C(R2)3
10-9 ～ 10-7 102 ～104 106～108 0.1 ～ 10
§2-3 Progress of living free radical polymerization
1. Living polymerization system containing Cr++ and peroxides
(3) Initiation efficiency
R group has big effect on the activity of radical pair, steric hindrance of the group is a key factor.
O
O
R
R
O
O
OO COOC
R=
O OO C OO C
OO
30
COOC
O
KPO
OO
20
C OO C
O
f (%)
10
BPO
0 0
5
10
15
20
25
Temperature (oC)
The influence of temperature on the f value
2. Initiation system by thermal decomposition
CH2 CH
CPh3
CH2 CH CPh3
Reversible termination
The reaction of free radicals
Ph3C CHPh2 heat Ph3C. + .CHPh2
Ph3C .
O2, ROH fast
Ph3COOH
Ph2CH.
O2, ROH fast
Ph2CHOOH
C8H17 O O B
. . heat C8H17 O + O B
Partially control polymerization of MMA
c. Triazolinyl radical
N RNNFra bibliotek. . heat
N
R +N
+nM
N
. R (M)n-1 M +
.N
N N
N R (M)n N
N
Controllable radical polymerization of MMA, St, MA and Vinyl acetate
(1) Ageing
OO C OO C
+ Cr2+
.O
O
C O + Cr3+ -O C
+
.O
O
C O Cr3+ -O C
(2) Initiation and propagation reactions
. O
O
C O Cr3+ -O C
MMA
. O
C
O
CH2
CH3 C
Cr3+ -O
O C
C=O
OCH3
(4) Developing new products
Products from homopolymerization are limited. The synthesis of new monomers is very difficult. Copolymerization can produce a variety of new
O
O
R=
Ketopinyl peroxide
(过氧化茨烷酮酰)
Initiation efficiency ( f ) = number of radical residues in the polymer/ number of radicals produced
The effect of polymerization temperature
• The bond between R1 and C(R2)3 can be C-C, C-O, C-N, C-S etc
• The bond between R1 and C(R2)3 should be weak and can be split homolytically in the polymerization condition
Initiation rate Conc of (mole/sec) active
species
(mol.L-1)
kapp
(L/molsec)
kt
τs
(L/mol-s) (Sec)
Anionic Very fast
10-4 ～ 10-2 2 ～3800 small
Long
Free radical
10-10 ～ 10-8
Ph2CH.