AbstractVarious low‐density polyethylenes ranging in initial weight‐average molecular weight (M̄w) from 7600 to 589000 having a ratio of M̄wto number‐average molecular weight (M̄n) of about 5 were irradiated by γ‐rays in vacuo at 30°C. Gel fractions were determined and analyzed by using the equation derived by Charlesby and Pinner. The following relationships were obtained when M̄wwas used as the molecular weight:documentclass{article}pagestyle{empty}begin{document}$$ begin{array}{rcl} r_g=2.85times 10^3 bar{M}_w^{-1}{rm C}hbox{=hskip-1pt=}{rm C}_0 ^{ - 0.21} q_0=5.98times 10^{-3}{rm C}hbox{=hskip-1pt=}{rm C}_0 ^{0.21} p_0=2.98times 10^{-3}{rm C}hbox{=hskip-1pt=}{rm C}_0 ^{0.21} end{array} $$end{document}wherergrepresents the gel point dosage (Mrad), CC0is the sum of the initial contents of terminal vinyl and vinylidene unsaturations (mole/g polyethylene), andq0andp0are the probabilities of crosslinking and main‐chain scission per monomer unit for a unit radiation dose in Mrad, respectively. Similar relationships to the equations described above were also obtained when M̄nwas used. From the results, 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 va
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