Photolysis of Copolymers in Solution

Preliminary investigations of the photolysis of poly-(methyl acrylate) homopolymer in solutions of methyl acetate, chloroform, methylene chloride and benzene were carried out. The light source employed was a Hanovia Chromatolite Lamp which produces, primarily, radiation of wavelength 2537A. The resulting chain scission reaction of the polymer was followed by monitoring the change in molecular weight of the polymer samples after varying periods of irradiation. Molecular weight analyses were determined using a Mechrolab High Speed Membrane Osmometer. The rate of chain scission of poly-(methyl acrylate) in solution was found to be independent of polymer concentration over the range 1 - 10% W/V, and to be little affected by the solvent used, other than that expected from optical filtering considerations. The two homopolymers of methyl methacrylate and methyl acrylate and a series of copolymers covering the entire composition range were prepared and the photodegradation of solutions of these samples was carried out. The characteristics of the photo-induced chain scission reaction across the composition range were studied and compared with those observed in the photolysis of thin films of the same polymer system. Differences observed, in particular an enhanced rate of chain scission of poly-(methyl methacrylate) in solution compared with that found in film photolysis, have been explained in terms of Glass Trans- ition Temperatures. Photo-oxidation has also been carried out with both thin films and solutions of these polymer samples and the relative degradation characteristics have been compared. Differences observed have been rationalised in terms of the subsequent reactions available to the polymer radicals obtained after the initial photo-induced cleavage of the ester side groups. Copolymers of methyl methacrylate with methacrylonitrile and styrene, covering the entire composition ranges, were prepared and irradiated in solution with methylene chloride. Methacrylonitrile, being structurally very similar to methyl methacrylate did not appear to have a significant effect upon the rate of chain scission of methacrylate-rich copolymers but it has been shown that the strong radiation-absorbing benzenoid nucleus of the styrene comonomer has a protective effect upon methacrylate-rich copolymers due to preferential absorption of the degradative radiation at stable aromatic sites. Some copolymers of methyl methacrylate and maleic anhydride were prepared and it has been shown that incorporation of even a very small quantity of maleic anhydride as comonomer greatly enhances the rate of the photo-induced chain scission reaction of methacrylate-rich copolymers