STABILITY AND DEGRADATION OF POLYMETHACRYLATES WITH CONTROLLED STRUCTURE

Thermal degradation behaviors for homo- and copolymers of methacrylates prepared by stereospecific living polymerizations as well as radical polymerization were studied. Thermal stability of radically prepared PMMAs can be improved by careful control of end groups and by incorporation of methyl acrylate into the chain. The mechanism of the stabilization was elucidated. Tacticity dependence of thermal stability of PMMAs was examined using isotactic and syndiotactic PMMAs with molecular weights (M(n)BAR) of 2,500-500,000 under nitrogen. Syndiotactic PMMAs showed higher degradation temperatures than the isotactic PMMAs of the same M(n)BAR when the M(n)BAR was lower than 25,000, and vice versa for the higher M(n)BAR. A similar M(n)BAR and tacticity dependence was observed in degradation in air, and the critical M(n)BAR was found to be about 10,000. These phenomena are discussed in terms of zip length of degradation and the difference in flexibility between isotactic and syndiotactic PMMA chains. Thermal degradation behavior of polymethacrylates were examined and classified as single-step and two-step degradations. This was related with the structures of the ester group. The glass transition temperatures of stereoregular homo- and copolymers of methacrylates are also discussed in some detail.