Thermal oxidation and photo- and biodestruction of the statistical copolymer of ethylene with carbon monoxide

Abstract

Thermal and photooxidation of the statistical copolymer of ethylene containing 1.5% carbonyl units -C(O)- by molecular O₂ was studied at 160–200°C in the presence and absence of phenyl-β-naphthylamine (PNA) antioxidant. The incorporation of a small number of -C(O)- groups into the polyethylene chain insignificantly decreased the rate of thermal (dark) oxidation but substantially accelerated oxidation under the action of light. At the same time, the oxidation of the copolymer occurred at a lower rate than the oxidation of pure polyethylene (PE), which was evidence of an important role played by intramolecular oxidation chain propagation in PE, which is disturbed already at a comparatively low fraction of foreign units. Phenyl-β-naphthylamine noticeably decelerated oxidation. The rate of polymer biodestruction was much higher than the rate of PE biodestruction. The influence of biodestruction on the physicomechanical properties of samples was studied by ultrasonic microscopy. The velocity of sound propagation in PE was somewhat lower compared with the ethylene-carbon monoxide copolymer (ECO). Clearly, the introduction of a small amount of CO molecules into the polyethylene chain changed the microstructure of PE. The structure of ECO was more ordered and denser because of plasticization by metabolites.