Mechanical relaxations in γ‐ray‐polymerized polyethylene

Dynamic mechanical properties of cold‐compacted films of polyethylene prepared by γ‐ray‐induced polymerization in bulk at 30°C are discussed in connection with the fine structure. The cold‐compacted films show a broad α‐relaxation at a lower temperature than do single‐crystal mats or melt‐crystallized polymer. From the effects of annealing and swelling by carbon tetrachloride on the relaxation, it is concluded that the α‐relaxation, like the α‐relaxation in the single‐crystal mats, originates from molecular motions within lamellar crystals. This is consistent with the finding that these films are composed of stacked small irregular lamellar crystals. The γ‐relaxation is also similar to that in crystal mats.