Phase Structure and Molecular Ordering

Phase Structure and Molecular Ordering.—Polyethylene remains the most popular subject for such studies, four papers dealing with solid polyethylene and two with molten polyethylene. Kitamaru e/ ah have studied the phase structure of bulk- and solution- crystallized polyethylene by broad-line n.m.r. Both types of samples show three components, a broad crystalline component, a narrow liquid-like component and an intermediate component 

Arai et al. have studied the effect of rolling and drawing on structure of polyethylene. A gradual decrease with temperature of the second moment of cold-drawn samples, absent in undeformed and hot-drawn samples, was attributed to intermediate regions less mobile than amorphous polymer. 

Other polymers whose phase structure has been studied are polypropylene, poly(tetrahydrofuran), and polyurethanes. The detection of four components in the wide-line spectrum of polypropylene fibres was claimed, the narrowest being attributed to absorbed water. In the study on poly(tetrahydrofuran), the molecular orientation in drawn and rolled sheets was examined. The anisotropy of the H wide-line spectra were well-explained by uniaxiai and double orientations of crystallites. Assink observed two-component free induction decays in polyurethanes at room temperature, attributed to glassy and rubbery constituents. Immediately after quenching from 170 °C, a linear polyurethane showed a continuum of domain compositions, but after a few hours, the original two-phase structure was re-established. 

Two-component systems have received some attention. - Poly(vinyl-idene fluoride -poly(methyl or ethyl methacrylate)s blends have been mentioned in the previous section. A study of compatibility in blends of poly(vinyl chloride) and ethylene-vinyl acetate copolymer (EVA) has been reported. Spin-lattice relaxation time measurements were bi-exponential corresponding to rigid [poly(vinyl chloride)] and mobile (EVA) phases. A precipitated mixture showed intermingling of EVA in the poly(vinyl chloride) phase, but phase separation occurred on heating. Cashell et a/. have contributed a short note on the effects of magnetic susceptibility inhomogeneities of lincwidths in carbon black-filled 

Cackovic, R. Hosemann, and J. Loboda-Cackovic, J. Polymer ScL, Polymer Letters, 1978,16,129. 

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