Charge-transfer complexes as polymerization inhibitors: 2. Studies on the mechanism of inhibition of the radical polymerizations of acrylonitrile and vinyl acetate using the amine-chloranil complexes

Abstract

The mechanism of inhibition of the bulk and solution polymerizations of acrylonitrile (AN) and vinyl acetate (VA) has been investigated using the charge-transfer complexes of triethylamine (TEA) and N, N-dimethylaniline (DMA) with chloranil. Complete inhibition is achieved by the complexes of both amines for the polymerizations of both monomers. The greater inhibiting efficiency of the TEA complexes is explained in terms of their greater stabilities. The results support the idea that inhibition by quinones involves electron-transfer from the polymeric radicals to the quinone forming molecular complexes of polymeric cations and semiquinone anions. The latter are the actual inhibitors so that the efficiency of inhibition depends on the feasibility of their formation which is determined by the stability of the complexes formed. The nature of the inhibition reaction products is determined by the extent to which the semiquinone anions are found as kinetically independent species in the polymerizing system. The mechanism suggested accounts for the great differences in the inhibiting powers of quinones for the polymerizations of various monomers.