Influence of iron(III) chloride on the degradation of the polyisoprene and polybutadiene

The influence of iron(III) chloride, FeCl3, on the degradation of polyisoprene and polybutadiene was investigated. From a 2(3) factorial design the effects of polymer concentration, FeCl3 concentration and temperature on the polymer degradation were evaluated. In solution, efflux time measurements, unsaturation degree and viscometric molar mass determinations were combined with H-1 NMR and infra-red spectroscopies. In the solid state, films of polymers doped with FeCl3 were exposed for several temperatures for different periods in air. It was verified that in solution the FeCl3 induces more degradation of polyisoprene than of poly butadiene. In the solid state, where the mobility of polymer chains is lowered, the FeCl3 induces more cross-linking of polybutadiene than of polyisoprene, if the polymers are exposed, for the same period, at temperatures equal or superior to 80 degrees C. The results lead us to conclude that the degradation occurs by scission of the double beads of the polymers, which is judged to be initiated by cationic species. It is suggested that the intermediate species formed in the polybutadiene chains are less stable than in the polyisoprene ones. The difference in stability would be due to the methyl group on the polyisoprene chains. (C) 2000 Elsevier Science Ltd. All rights reserved.