Approaches towards a comprehensive theory of the cationic polymerisation of olefins

Some of the factors which influence, or must be contained in, a Comprehensive Theory of the cationic polymerisation of olefins are discussed from new points of view, starting from the author's new theory concerning initiation by metal halides. Alleged determinations of the rate constant k are criticised because they ignored two equilibria which make the concentration of growing polymer chains [P ] in general less than the nominal concentration, c0, of initiator. One of them is a binary ionogenic equilibrium involving metal halide MtXn and polymer halide PnX. The other is between metal halide and olefin. An equation relating [P ] to c0 is deduced which takes account of these equilibria. The importance of the second equilibrium is illustrated by the way in which it provides simple explanations of hitherto obscure phenomena. Some of these arise during the interaction of aluminium halides with olefins in different circumstances, others concern the different interactions which can take place between titanium tetrachloride and 1,1‐diphenylethylene. The fact that titanium tetrachloride appears to be able to initiate without co‐initiator in some systems, but requires one in others is explained by the self‐ionisation of the metal halide and the effects of impurities.