DECOMPOSITION OF VINYLIDENE-CHLORIDE COPOLYMERS IN THE PRESENCE OF SELECTED TRANSITION-METAL HALIDES

Because of their high barrier to the transport of oxygen and flavor an d aroma molecules, vinylidene chloride polymers occupy a position of p rominence in the polymer plastics packaging industry. However, at proc essing temperatures these polymers tend to undergo degradative dehydro chlorination. The dehydrochlorination reaction is a typical chain proc ess which is initiated at a defect site (allylic dichloromethylene uni t), present in the polymer as a consequence of random dehydrohalogenat ion during polymerization, drying, etc. This initial dehydrohalogenati on is thought to be catalyzed by metal ions formed by interaction of t he polymer with equipment walls or present by other means. To test thi s, a series of blends of metal halides (5 wt%) with a vinylidene chlor ide/methyl acrylate (5 mol%) copolymer has been examined by thermograv imetry in nitrogen. All the polymer/metal halide blends were more pron e to degradation than the untreated polymer. The effectiveness of the metal halide in promoting the degradative dehydrochlorination correlat es well with the Lewis acidity/Pearson hardness of the metal ion.