The photooxidative gelation of cis-1,4- polybutadiene in solution

Irradiation of dilute solution of cis‐1,4‐polybutadiene in carbon tetrachloride with UV light in the presence of air causes fast formation of white precipitate—insoluble gel. It has been shown that carbon tetrachloride was effective photosensitizer for oxidation of cis‐1,4‐polybutadiene. Separated sol and gel fractions were analysed by infrared spectroscopy for better understanding of gelation process and structure of the gel. Three stages were detected in the process of oxidative photogelation of cis‐1,4‐polybutadiene in carbon tetrachloride solution: pre‐gelation(sol‐stage), gelation (sol/gel‐stage) and post‐gelation (gel‐stage). In the first stage intensive photooxidative reactions between cis‐1,4‐polybutadiene, carbon tetrachloride and oxygen take place, giving products with high content of hydroperoxide and bounded chlorine. When hydroperoxide and chlorine content reached critical value, precipitation‐gelation takes place. It is proposed sequence of free radical reactions which involves: photolysis of carbon tetrachloride to free radicals, addition of solvent radicals to the double bonds of rubber followed by combining of resulting radicals with oxigen to chlorinated polymeric peroxy radicals. Initially formed gel is peroxidic in nature, which photolyses to the more stabile ether gel by prolonged irradiation.