A direct method has been developed for determining G(crosslinks) for irradiated polymers using the analytical ultracentrifuge. The sedimentation velocity technique is employed to follow changes in the molecular weight of a narrow distribution polystyrene sample irradiated in vacuum with 60Co γ‐rays. It is shown that G(crosslinks) can be determined at low doses before significant structural changes have occurred in the polymer. At about one‐fifth of the gel dose G(crosslinks) was found to be 0.019 compared to a value of 0.040 obtained from gel‐sol fraction measurements. It is concluded that G(crosslinks) may increase with dose due to processes such as the addition of radicals to double bonds formed during the irradiation.
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Kells et al. (1968) studied this question.
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