Thermal degradation of styrene-methacrylic acid copolymers

Copolymers of styrene and methacrylic acid (MAA) with widely differing compositions have been studied by thermal volatilisation analysis (TVA) and thermogravimetry. The condensable volatile degradation products have been identified after separation by subambient TVA. The cold ring fraction (tar/wax products) and the structural changes in the residue in the course of degradation have also been examined. The copolymers are intermediate in stability between polystyrene (PS) and poly(methacrylic acid) (PMAA). The degradation products are mainly those expected by comparison with those obtained from the homopolymers, but methacrylic acid is formed in greater amount in the copolymer degradation and the distribution of MAA units leads to less intramolecular dehydration. Anhydride rings formed, however, reduce the zip length of depolymerisation to monomers, and both rings and isolated MAA units reduce the possibilities for transfer by polystyryl radicals.