Reactivities of substituted acyclic and cyclic enolethers in photoinduced cationic polymerization

Abstract

The reactivities of different acyclic and cyclic enolethers in photoinduced cationic polymerization are investigated. While an β-methyl moiety leads to an increase of reactivity of the enolether in cationic polymerization, methyl substituents in β-positions decrease it. Two β-subtituents prevent homopolymerization completely. Ring strain in cyclic enolethers leads to a higher reactivity but is overruled by effects of sterical hindrance. It is shown that the type of photoinitiator affects the reaction rate of photoinduced cationic polymerization. In this respect different pyridinium salts were investigated. The difference in reactivities of these photoinitiators is due to the correspondence of their absorption spectrum with the emission spectrum of the source of UV irradiation used. Inefficient molar masses of polymers from β-substituted enolethers are explained by side reactions which can be suppressed by lowering the reaction temperature.