Effect of double bonds on the γ-radiation-induced crosslinking of polyethylene

Various low-density polyethylenes ranging in initial weight-average molecular weight from 7600 to 589,000 having a ratio of weight-average molecular weight to number-average molecular weight of about 5 were irradiated by γ rays in vacuo at 300C. Gel fractions were determined and analyzed by using the equation derived by Charlesby and Pinner. The gel point dosage (Mrad), the sum of the initial contents of terminal vinyl and vinylidene unsaturations (mole/g polyethylene), and probabilities of crosslinking and main-chain scission per monomer unit for a unit radiation dose in Mrad. It was concluded that terminal vinyl and vinylidene unsaturations play an important role for the gel formation in the γ-radiation-induced crosslinking of polyethylene in vacuo at room temperature. (U.S.)