Mechanical degradation of organosilicon polymers

Abstract

Many studies have been made in recent years, in which the EPR method was used to elucidate the mechanism of mechanical degradation of polymers. It was shown that degradation of organic synthetic and natural polymers takes place by the radical mechanism. An analysis of EPR spectra of primary “mechanical” free radicals formed during polymer decomposition suggests that homolytic breakdown of chemical bonds in chains of main macromolecular valences in the initial mechano-chemical stage [1–3]. To stabilize active free radicals formed during the decomposition of polymers, experiments should be carried out at low temperature. Drilling or milling of polymers in liquid nitrogen is a simple method of decomposing polymers at low temperature, which ensures intensive cooling of the products of decomposition. During the decomposition of polymers under these conditions EPR signals are always observed which indicate the formation of free radicals. “Mechanical” free radicals were obtained from many organic polymers decomposed in liquid nitrogen. EPR spectra have been reported in separate papers [1,2, 4–7] of free radicals stabilized at liquid nitrogen temperature in pieces of polyethylene, polyvinylchloride, polytetrafluorethylene, polyisobutylene, polymethyl methacrylate, polyvinylacetate, polystyrene, polyisoprene, polyethylene sulphide, polypropylene sulphide, thiokols, ebonite, polycarbonate, polyepoxide, polycaprolactam, polyurethane and keratin proteins. We also observed EPR spectra of free radicals in polypropylene and polyethylene terephthalate.