Effects of cis–trans isomerization on the photopolymerization behavior of N-vinyl amide monomers

Abstract

Photopolymerization behavior of three commercially available N-vinyl amide monomers was compared in air and nitrogen. Additionally, a series of N-substituted N-vinyl formamides was synthesized and their reactivities under photolytic initiation conditions (1 mol% 2,2-dimethoxy-2-phenylacetophenone (DMPA) at 40°C) were studied. Of the five derivatives synthesized, only the benzyl derivative and the N-vinyl formamide (NVF)/methacrylate derivative showed any reactivity toward free radical bulk photopolymerization. It was determined by 13C-NMR analysis that, while the more reactive NVF exists predominantly in the trans conformation with respect to the planar C–N amide bond, the cyclic commercial monomers and the N-substituted derivatives of NVF exist totally or mostly in the cis conformation. The increased cis isomer content has a deleterious effect on polymerization. The cis amide bond is less reactive due to electronic and steric hindrance around the propagating radical center, and the predominance of this isomer leads to low overall reactivity to photolytically catalyzed bulk polymerizations of these monomers.