The thermal degradation of polyvinyl compounds - III. The effect of inhibitors and end groups on the degradation of polymethyl methacrylate

Abstract

An investigation has been made of the effect of various end groups upon the degradation of polymethyl methacrylate chains. Inhibition of the degradation reaction by 1, 4 diamino anthraquinone has also been studied. That small amounts of such a substance do inhibit the reaction shows conclusively that the mechanism is a chain reaction involving free radicals. 1, 4 diamino anthraquinone and its leuco compound have equal inhibitory power indicating that the dyestuff is the active agent. Experiments show that if leuco compound is used, it is very quickly converted to the dyestuff. These experiments, combined with viscosity measurements, gave additional evidence that in degradation the molecules break initially at the ends. Comparison of the rates of degradation of benzoyl peroxide catalyzed polymers, photopolymer and polymer initiated and terminated by diphenyl cyanomethyl radicals show that double and single bond ends, formed by disproportionation, break most easily. The energies of activation of degradation through them are 30,000 and 42,000 although it is difficult to decide which is which. The energy of activation for degradation through diphenyl cyanomethyl end group is 47,000. The energetics are discussed.