Methyl methacrylate/2,2-chloroacrylonitrile and styrene/2,2-chloroacrylonitrile copolymers of various molar ratios have been prepared by free-radical, addition polymerisation and characterised by nuclear magnetic resonance spectroscopy and microanalysis. The photodegradation by 254nm radiation of thin copolymer films has been studied at ambient temperatures. Spectroscopic examination of the residual films, separation of degradation products by a recently developed, low-temperature, thermal volatilisation analysis technique, cumulative, quantitative product analysis and product identification by spectroscopic techniques have enabled the photodegradation processes to be studied in depth. The results indicate that, as the proportion of 2,2-chloroacrylonitrile in the copolymer with methyl methacrylate is increased, the well-established degradative behaviour of poly(methyl methacrylate)--- a rapid decrease in molecular weight and formation of products from ester decomposition--- is gradually replaced by crosslinking, unsaturation, insolubility, the production of hydrogen chloride from 2,2-chloroacrylonitrile units and methyl chloride from both monomers. Around the 1 : 1 molar ratio a highly absorbing surface layer begins to be formed. The effect of 2,2-chloroacrylonitrile units on polystyrene photodegradation is less marked. The major reaction is hydrogen chloride formation. For the same molar ratio, the rate of formation of hydrogen chloride from 2,2-chloroacrylonitrile copolymers with styrene is considerably greater than with methyl methacrylate. This is attributed to the different absorption coefficients of radiation of the two co-monomers. Solvent participation in photodegradation reactions is indicated by anomolous molecular weight measurements on the methyl methacrylate system and by post-irradiation absorption spectra of copolymer films of both systems. The effect of pre-irradiation on the thermal degradative behaviour of copolymer films has been studied. The nature of the degradation products remains unchanged but the effects of crosslinking and unsaturation on the methyl methacrylate system are reflected in thermogravimetric analyses and differential condensation thermal volatilisation analyses on the system. The initiation processes involved, the scissioning reactions, the development of unsaturation in the copolymers and the related discoloration of copolymer films are discussed in the course of the work. Comparisons are drawn with studies on similar polymer systems and various references are listed which have been found relevant to the present study
