PHASE-RESTRICTED RADIATION CROSS-LINKING IN SEMICRYSTALLINE POLYOLEFINS INVESTIGATED BY 2-DIMENSIONAL SOLID-STATE NUCLEAR-MAGNETIC-RESONANCE

The 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 H-1 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.