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.