Page 187 - Carrahers_Polymer_Chemistry,_Eighth_Edition

150 Carraher’s Polymer Chemistry

TABLE 5.1
Major Technique Used in the Production of Important Vinyl Polymers
Free Radical Low-density polyethylene (LDPE)
Poly(vinyl chloride)
Poly(vinyl acetate)
Polyacrylonitrile and acrylic fi bers
Poly(methyl methacrylate)
Polyacrylamide
Polychloroprene
Poly(vinyl pyridine)
Styrene–acrylonitrile copolymers, SAN
Polytetrafl uoroethylene
Poly(vinylene fl uoride)
Acrylonitrile–butadiene–styrene copolymers (ABS)
Ethylene-methacrylic acid copolymers
Styrene–butadiene copolymers (SBR)
Nitrile rubber (NBR)
Polystyrene
Cationic Polyisobutylene
Butyl rubber
Polyacetal

Anionic Thermoplastic Olefin Elastomers (Copolymers of
butadiene, isoprene, and styrene
Polyacetal
Complex High-density polyethylene (HDPE)
Polypropylene
Polybutadiene
Polyisoprene
Ethylene–propylene elastomers

5.1 CHAIN GROWTH POLYMERIZATION—GENERAL
The next three chapters will deal with polymers formed from chain growth polymerization. Chain
growth polymerization is also called addition polymerization and is based on free radical, cationic,
anionic, and coordination reactions, where a single initiating species causes the growth of a polymer
chain.
The kinetic chain reaction typically consists of three steps—initiation, propagation, and termina-
tion. The initiators for free radical, anionic, and cationic polymerizations are organic radicals, car-
banions, and carboniums. Chain growth is exothermic with the polymerization mainly controlled
by the steric and resonance factors associated with the monomer. Generally, the less resonance sta-
bilization the more heat is given off during the reaction. Also, the greater the steric factors the less
heat is given off during the polymerization.

5.2 CATIONIC POLYMERIZATION
The art of cationic polymerization, like that of many other types of polymerization, is at least a century
old. However, the mechanisms for these reactions have only recently become better understood.
The first species produced in cationic polymerizations are carbocations, and these were unknown

as such before World War II. It is now known that pure Lewis acids, such as boron trifl uoride and
aluminum chloride, are not effective as initiators. A trace of a proton-containing Lewis base, such

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