Radiolysis of polyisobutene. Part I. Yields of fractures, double bonds, and gas

Purified polyisobutene with approximately a random molecular weight distribution and a number‐average molecular weight of 3.5 × 105 was irradiated in vacuo at about 25°C. with 4 M.e.v. electrons. The degradation of the polymer was studied by osmometry and viscometry and the G (fracture) value determined as 4.1. The G value for total unsaturation was determined as 5.3 by a chemical method suitable for olefins branched in the vicinity of the double bond. Little or no internal unsaturation was detected by ozonolysis of the irradiated polymer. Hydrogen and methane were formed with G values of 1.3–1.6 and 0.8–0.5, respectively. At doses greater than about 10 Mrad all the above G values decreased. The G value for isobutene formation (≤ 0.1) remained approximately constant up to a dose of at least 150 Mrad. On lowering the temperature of irradiation to −196°C. the yield of fractures was markedly decreased while the yield of hydrogen plus methane was scarcely affected. This is interpreted as evidence that the degradation reaction is due predominantly to the direct fracture of carbon–carbon bonds rather than to any reaction associated with gas formation. The observed ratio of double bonds to fractures is shown to be consistent with this interpretation.