difference between cationic and anionic polymerization
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Answer:
Anionic Polymerization Cationic Polymerization
The rate of polymerization is usually slower than that of cationic polymerization because electron-withdrawing substituents on the anionic initiator stabilize the negative charge through charge delocalization.
Cationic polymerization reactions proceed at high rates both at high and (very) low temperatures. A uniform and constant reaction condition, however, is difficult to maintain.
All monomers with (strong) electronegative substituents polymerize readily in the presence of anionic initiators. This includes styrenes, dienes, (meth)acrylates, aldehydes, epoxides, acrylonitriles and cyanoacrylates.
Monomers that polymerize in the presence of cationic initiators include isobutylene, styrene, alpha-methylstyrene, butadiene, vinyl alkyl ethers and many other monomers having electron-donating substituents.
Anionic polymerization reactions are rather insensitive to temperature and can be carried out at both elevated and very low temperatures.
Cationic polymerization reactions are sensitive to temperature. Both the reaction rate and molecular weight rapidly decrease with increasing temperature.
Anionic polymerization reactions typically yield more regular polymers with less branching, more controlled tacticity and narrow molecular weight (MW) distribution. End groups can be tailored for further reactivity.
The high reactivity of the cationic growth centers leads to undesirable side reactions, such as chain transfer and chain termination, which, in turn, lead to high branching, lower MW and broader MW distribution.
Anionic polymerizations are difficult to carry out and are only used on an industrial scale when polymers with regular structure and narrow MW distribution are required.
Cationic polymerizations are difficult to control and are limited to olefinic monomers. Its main commercial use is the production of polyisobutylene (PIB) and butyl rubber.