Unsaturation changes and other radiolytic reactions in polyethylene. II. An examination of crosslinking with gel permeation chromatography

A simple method of determining crosslink yields and examining crosslink statistics in polymers is described. In this method the soluble fraction of materials crosslinked to well above their gel point is examined with gel permeation chromatography and compared with the original material. The results of such an examination of the soluble fractions of irradiated polyolefins indicate that the random statistical crosslinking mechanism first suggested by Charlesby is followed closely by low‐density polyethylenes. The high‐density polyethylenes examined show deviations from statistical behavior, which may be attributed to dimerization or endlinking through vinyl decay. However, other factors may also be involved. The results suggest that G (crosslinks) does not change significantly with dose and that the ratio of chain scission to crosslinks is less than 0.03 in the range up to 80 Mrad in a low‐density polyethylene.