Phase‐restricted radiation crosslinking in semicrystalline polyolefins investigated by two‐dimensional solid‐state nuclear magnetic resonance

Abstract

AbstractThe utility of two‐dimensional wideline separation (2D WISE) NMR in following the phase dependence of the radiation‐induced crosslinking of multiphase materials has been demonstrated. Crosslink production in semicrystalline polyolefins by high‐energy electron irradiation in air was monitored via the experimentally resolved 1H lineshapes of the respective amorphous and crystalline regions. It was shown that radiation‐induced crosslinks can be primarily restricted to one phase or the other by proper functionalization, or nonfunctionalization, of the host polymer. Poly(1,23‐tetracosadiyne), a diacetylene‐functionalized polyethylene, was synthesized and shown to predominantly undergo crystalline‐phase crosslinking for dosages of 100 kGy and less. Thus, chain mobility within amorphous regions may be maintained upon radiation‐induced crosslinking. In comparison, linear polyethylene exhibited amorphous‐phase crosslinking for electron beam radiation dosages of at least 400 kGy; application of 2D WISE NMR represents a direct method for following this well‐known process.