TABLE OF CONTENTS Copolymerization involves the simultaneous chain polymerization of a mixture of two or more monomers [89 92].Aside from the general kinetic considerations which govern these chain reactions, as described earlier, there is imposed an additional feature, i.e., the relative participation of the different monomers during the growth of the chain. This new parameter is most important, since it controls the composition of the copolymer. Systems involving more than two monomers are difficult to resolve in this respect, but it has been found possible to treat the case of a pair of monomers with relative ease [91, 93 95].
In the chain addition polymerization of two monomers, regardless of the mechanism involved, the growing chain always must make a choice of reacting with one of the two monomers. Furthermore, there are two kinds of growing chains, depending on which type of monomer unit occupies the growing end. Thus, four types of propagation steps can be written as follows for any chain copolymerization of two monomers assuming that the reactivity of the chain end depends only on the chain end monomer unit (terminal model [89]):
where 
and M 1 refer to the growing chain and the monomer, respectively, as before, while the subscripts refer to the two kinds of monomer in the mixture. It can be seen that these four propagation reactions lead to four propagation rate constants, as shown. Hence the rate of consumption of each monomer may be expressed by the...
