Recent developments in alternating copolymerization

Alternating copolymers exhibit several characteristic types of behavior. Their glass points T g are sometimes derived from the mean of two homopolymers. It was found that T g of copolymers of different degree of alternation can be expressed as a molar mean of each diad involved in the copolymer. The melting points are not clear except for some polymers of extremely high degree of alternation. High orientation was observed on stretching and greatly enhanced tensile property is exhibited. Alternating copolymers constitute versatile material such as rubber, functional polymer. etc. There have been developed several methods for the preparation of alternating copolymers. For the copolymerization of olefin and diolefin a modified Ziegler catalyst was developed. By controlling the number of coordination sites of the catalyst, the alternating coordination of olefin and diolefin is. made possible. The polymerization mechanism was established by determining the polymer structure using ozonolysis. For the copolymerization of an electron‐donating monomer and an electron‐accepting monomer two mechanisms are considered, one involving the donor‐acceptor intermediate complex and the other without such complex. The discrimination of these mechanisms is very difficult because there is little difference in the stereoregularity as well as sequence regularity according to the mechanisms. In the copolymerization of butadiene and acrylic monomer complexed with EtA1Cl 2 and VOC1 3 , there exists a maximum rate of polymerization at a definite monomer composition which is not changed by the amount of EtA1Cl 2 . This fact can be explained only by the complex mechanism. Other interesting methods for the preparation of the alternating copolymer, such as copolymerization through a zwitterion intermediate and ring‐opening polymerization, are reviewed.