Polymerization of acrylonitrile by electron transfer initiation

The homogeneous polymerization of acrylonitrile by electron transfer initiators is investigated. In a rigorously purified system at low temperatures it is demonstrated that “living” polyacrylonitrile is formed, and that its molecular weight can be predetermined. The number‐average molecular weight of “living” polyacrylonitrile is approximately given by 2M/I, where M represents grams of monomer and I is the number of moles of the initiator. For polyacrylonitrile prepared by homogeneous anionic polymerization with an electron‐transfer initiator, it is found that the viscosity average molecular weight calculated by using the conventional values of K and α in the Mark‐Houwink equation is considerably smaller than the osmotic number‐average molecular weight. This clearly indicates a structural difference between the free‐radical and anionic polyacrylonitrile; the anionic polyacrylonitrile appears to have a highly branched structure formed by a chain transfer process to the polymer.