Thermogravimetric assessment of the suitability of cyclohexa-2,5-dienecarboxylates as stabilizers for vinylidene chloride polymers

Vinylidene chloride (VDC) copolymers display excellent barrier to the transport of oxygen and other small molecules as well as flavor and aroma constituents of food items. For this reason they occupy a place of prominence in the barrier plastic packaging industry. However, they tend to undergo degradative dehydrochlorination during processing. To prevent the development of objectionable color the degradation reaction must be controlled. The dehydrochlorination reaction is a typical radical chain process with an allylic carbon, chlorine atom radical pair as the chain propagating species. The presence of additives that might interrupt this process by scavenging radical moieties, particularly chlorine atoms, should have a stabilizing influence on the polymer. 1,4-Cyclohexadienes are known to be good hydrogen atom transfer agents. Incorporation of this structure into a compound that is nonvolatile, compatible with the polymer, and approved for food contact might generate an effective stabilizer. Accordingly, 2,5-cyclohexadienecarboxylates have been synthesized and used to prepare blends (1, 5 and 10 wt.%) with a standard VDC/methyl acrylate (9 wt.%) copolymer. The stability of the various blends has been determined by thermogravimetry.