Page 268 - Carrahers_Polymer_Chemistry,_Eighth_Edition

Copolymerization 231

O O
N
R R 1 R 1 R R 2
HO OH + O NH NH O O
N R 2
(7.31)
O
Flexible polyester Diisocyanate Flexible block copolymer
or polyether

A related product is formed from the analogous reaction using hydroxyl-terminated poly(ethylene
oxide) with aromatic diacids to form a segmented aromatic polyester block copolymer that is sold
under the trade name of Hytrel.
Poly(ethylene oxide) itself is made from ethylene oxide through a base catalyzed ring-opening
polymerization. While the major use of poly(ethylene oxide) is in the manufacture of polyurethane
products, including foams, it can be synthesized giving viscous liquids to solids depending on the

molecular weight. It is used as surfactants, functional fluids, thickeners, lubricants and as plasticiz-
ers. Further, the circuit boards that hold the electronic components of computers are made from
poly(ethylene oxide).
The most widely used chain-reaction block copolymers are those prepared by the addition of
a new monomer to a macroanion. AB and ABA block copolymers called Soprene and Kraton,
respectively, are produced by the addition of butadiene to styryl macroanions or macrocarbanions
(7.32). This copolymer is normally hydrogenated (7.33).

R
R

(7.32)

R
R

B (7.33)

A A

Today, new copolymers are making use of the hard-soft block strategy where the hard segment
is a block portion as polyethylene that readily crystallizes forming a physical crosslink. The soft
segment consists of blocks formed from α-olefi ns such as 1-butene, 1-hexene, and 1-octane where
the substituted alkane-arm discourages crystallization.
A number of siloxane ABA block polymers have been formed. Copolymers of dimethylsiloxane
(A)-diphenylsiloxane (B)-dimethylsiloxane (A) have been synthesized by the sequential polymeri-
zation of reactants. The diphenylsiloxane block acts as a hard block, and the more fl exible dimeth-
ylsiloxane blocks act as soft blocks.
Hard segments have also been introduced using p-bis(dimethylhydroxysilyl)benzene with the
soft block again being dimethylsiloxane.

9/14/2010 3:39:56 PM
K10478.indb 231
K10478.indb 231 9/14/2010 3:39:56 PM