Vinylidene chloride copolymers form the base for a significant segment of the barrier plastic packaging industry. While these materials have many superior properties they tend to undergo degradative dehydrochlorination at process temperatures. In an attempt to identify polymers which might display increased thermal stability, a series of vinylidene chloride/2-[3,4-(1,1-dioxycyclopentyl)phenyl]ethyl acrylate copolymers has been examined by thermogravimetry. These polymers contain a 3,4-dihydroxyphenyl pendant masked as the cyclopentanone ketal. In principle, this moiety could consume evolved hydrogen chloride (to prevent its interaction with the walls of process equipment) to expose phenolic groups which might scavenge chlorine atoms. Both processes should enhance the stability of the polymeric system. In practice, copolymers containing 1.2, 2.6, 4.2 and 4.9 mol% 2-[3,4-(1,1-dioxycyclopentyl)phenyl]ethyl acrylate all undergo thermal degradation at approximately the same rate. The rate of decomposition of these copolymers, as reflected in both the rate constants (k(i)) for initiation and propagation (k(p)) Of the degradation reaction, is not significantly different from that of the vinylidene chloride homopolymer.