The oxidative decomposition of poly(methyl methacrylate)-crosslinked poly(butyl acrylate) core-shell polymers

The thermo-oxidative stability of polymer samples based on submicrometric three-layer bead particles was evaluated by dynamic thermogravimetry (TG). Polymer particles synthesized in emulsion consist of a poly(methyl methacrylate) core, a butyl acrylate crosslinked copolymer interlayer and a methyl methacrylate butyl acrylate copolymer shell. The comparative mass loss study in oxygen and nitrogen leads to the following conclusions. Oxygen retards the decomposition to volatiles of the polymer sample isolated from the emulsion in powder form at lower temperatures at the beginning of the process. The second stage of the TG record which is relevant to the mass loss of the butyl acrylate copolymer shows a higher rate of formation of volatiles. In oxygen, the densified polymer samples prepared by melting the particle polymer powder do not show a substantial difference compared to the TG curves observed for powder samples. However, the thermodegradation in nitrogen is shifted by more than 60 degrees C to higher temperatures. We explain the different course of the TG curves by a denser packing of core-shell particles in the processed samples. The diffusion of reaction products from the reaction cage is slowed down with a positive effect on thermostability. Oxygen acts in the opposite way through the oxidative polymer chain scission of macromolecules and increases the rate of initiation of depolymerization. Increasing the rate of heating of the sample in oxygen only has a small effect on shifting the volatilization to higher temperatures. This is less evident than in nitrogen. (C) 1997 Elsevier Science Limited.