The thermal stability of some vinylidene chloride copolymers

Vinylidene chloride (VdC) was copolymerised with a series of acrylates and methacrylate monomers to investigate the effect of increasing side chain le ngth on thermal stability and oxygen barrier behaviour. Suspension polymeri sation was used, and the comonomer contents were 7.5 and 12.5 mol%. The hom o-polymer was also synthesised and investigated. Rates of dehydrochlorinati on were measured at 180, 195 and 210 degrees C and the activation energies calculated. The volatile degradation products were examined using chromatog raphy and the degradation residue by IR spectroscopy. Percentage crystallin ity was measured by Xray diffraction and oxygen permeation was measured usi ng the Mocon method. The results showed that the VdC-methacrylate copolymer s had much higher rates of dehydrochlorination and lower activation energie s than the VdC-acrylate copolymers. The behaviour of the homopolymer was in termediate. This relative instability of the methacrylate copolymers is tho ugh to be due to them having greater block character, and therefore a highe r potential for unzipping reactions, and also to the possibility of a neigh bouring group activation process. The crystallinities of the copolymers was less than that of the homopolymer but crystallinity was not shown to be a major factor in determining barrier properties. The VdC copolymers with the best balance between their thermal stability and barrier behaviour were th ose with methyl acrylate, which are presently used commercially. Increasing the acrylate comonomer side chain length confers no stability advantage. ( C) 1999 Elsevier Science Ltd. All rights reserved.