RADIATION DEGRADATION OF ELASTOMERS

The dependence on molecular structure of the effects of high energy ra diation on a variety of elastomers has been examined by H-1- and C-13- NMR spectra in solution, swollen gel, and the solid state. Scission an d crosslinking yields obtained for an ethylene-propylene copolymer by NMR were in agreement with values from soluble fraction analysis, show ing that the NMR method was quantitative and that the radiation-induce d scission and crosslinking events were randomly spatially distributed . High crosslinking yields in cis-1,4-polybutadiene indicated a kineti c chain reaction producing crosslinks in clusters. A variety of new ch ain ends from main-chain scission were observed in polyisobutylene, pr oviding evidence on the validity of proposed radiolysis mechanisms. In chlorobutyl rubber, crosslinking occurred with very high yield by rea ction of both C-Cl and C=CH-2 groups in the chlorinated isoprene units , but decreased after quite low doses due to depletion of these groups .