Page 269 - Carrahers_Polymer_Chemistry,_Eighth_Edition

232 Carraher’s Polymer Chemistry

CH 3
CH 3 CH 3

HO Si Si OH HO Si O
+
CH CH H
3
3
CH 3
(7.34)

CH 3 CH 3

R Si Si O
CH 3
Si
CH
CH 3 3
H C
3
O R
Block copolymers, with segments or domains of random length, have been produced by the
mechanical or ultrasonic degradation of a mixture of two or more polymers such as hevea rubber
and poly(methyl methacrylate) (PMMA) (Heveaplus).
Thus, there have been prepared a number of different block copolymers, including a number that
utilize the hard-soft strategy.

7.5 GRAFT COPOLYMERS
The major difference between block and graft copolymers is the position of the second kind of unit.
Thus, information that applies to block copolymers can often be applied to graft copolymers. So,
domains where physical cross-linking occurs via crystallization can occur in either block compo-
nents or within graft copolymers where the necessary symmetry occurs.
Graft copolymers of nylon, protein, cellulose, or starch, or copolymers of vinyl alcohol have
been prepared by reaction of ethylene oxide with these polymers. Graft copolymers are also pro-
duced when styrene is polymerized by Lewis acids in the presence of poly-p-methoxystyrene. The

Merrifield synthesis of polypeptides is also based on graft copolymers formed from chloromethay-
lated polystyrene. Thus, the variety of graft copolymers is great.
The most widely used graft copolymer is the styrene-unsaturated polyester copolymer (Equation
7.35). This copolymer, which is usually reinforced by fibrous glass, is prepared by the free radical

chain polymerization of a styrene solution of unsaturated polyester.

O
O O R H 2 C
O O R O
O
+ R
R 1 O (7.35)
R

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