The thermal degradation of polyvinyl compounds IV. The thermal degradation of the methyl methacrylate copolymers with glycol dimethacrylate and acrylonitrile

Abstract

The effect upon degradation of cross-links, formed by copolymerizing small amounts of glycol dimethacrylate with the methyl methacrylate, and small amounts of acrylonitrile units in the chains has been investigated. Cross-links make no difference to the degradation characteristics according to rate measurements. Molecular weights could not be measured in this case owing to the insolubility of the polymer. The methyl methacrylate-acrylonitrile copolymer degrades in quite a different way from polymer composed of homogeneous methyl methacrylate chains. In this case the chain ruptures initially at or near the acrylonitrile units, the molecular weight falling very rapidly in the initial stages of the reaction. One side of the break is terminated by an acrylonitrile unit which cannot degrade but the other side may sooner or later degrade to the next acrylonitrile unit along the chain. The induction period observed is probably due to the time taken to build up an appreciable concentration of such degradable ends. A quantitative calculation agrees well with this theory.