Nuclear magnetic resonance study of molecular motions in some crystalline polymers

Nuclear magnetic resonance linewidth studies are made concerning the molecular motions in crystalline polymers moh as polyethylene, polytetrafluoroethylene, and trans-1,4-polybutadiene. (1) The γ (local mode) relaxation of polyethylene is studied based on the temperature variation of mobile fraction. The range of the β (primary) dispersion of linear polyethylene is shown to spread far wider than that of branched polyethylene, whereas its lower limit (Tg−) is the same for the two. (2) Concerning polytetrafluoroethylene, a third NMR component is found in addition to narrow and broad-line components, and the third phase of molecular aggregation is assumed to be intermediate between the amorphous and crystalline phases. The notion of the intermediate phase (an array of rodlike molecules) is instrumental in clarifying the complicated viscoelastie behavior by admitting two glass transitions in the polymer. (3) At the solid-phase transition of trans-1,4-polybutadiene, a huge-scale motional narrowing of the NMR absorption line takes place, indicating the onset of rodlike rotation of the molecules belonging to the crystalline phase. Above the phase transition temperature, the polymer crystal is “plastic”.