Broad line NMR studies on radiation effects on polymers

Our previous studies on the radiation effect on polymers made by using the broad line (BL) NMR technique are autoreviewed with emphasis on the usefulness of this technique. The BL NMR was widely applied, before the prevalence of the modern pulse NMR technique, to study the change of molecular motion caused by either the crosslink or the main-chain scission in solid polymers, since both line-shape and line-width of the BL NMR are sensitive to the molecular motion. Low-and high-density polyethylenes grafted with butadiene by γ-rays were examined before and after the crosslinking induced by heat-treatment with dicumyl peroxide. The crosslinking was found to occur between grafted polybutadiene branches. Polytetrafluoroethylene irradiated with neutron-beam was examined before and after heat-treatment. The results show that heat-treatment causes the formation of paracrystals of radiation-scissored polymer chains and hinders the molecular motion. Response of fluorinated ethylene-propylene copolymer to the neutron-irradiation was quite different: a small fluoropropylene fraction inhibited the paracrystal formation. (author)