Abstract
Nuclear magnetic resonance in solid polyβ2βpyrrolidone has been studied over the temperature range 77β450Β°K. Experimental evidence concerning the differently ordered regions that contribute to the composite NMR curves has been obtained. Experimental techniques and results are described in detail. A detailed comparative interpretation of twoβcomponent NMR curves as a function of temperature is offered in terms of motion in differently ordered regions. The width of the component corresponding to the crystalline regions was found to be independent of temperature over a certain range above that of liquid nitrogen; this is taken to indicate a rigid structure. At higher temperatures there is a gradual decrease in line width indicating increasing segmental molecular motion. The NMR line width representing amorphous regions was found not to change over approximately the same range of low temperatures; it then decreases faster with increasing temperature than that of the crystalline regions; it finally decreased sharply and became the narrow component above the glass transition temperature. The glass transition temperature in polypyrrolidone appears to decrease with increasing water content. Comparison of the temperature of glass transition of dry polypyrrolidone with those of other polyamides supports the observation that the temperature of this transition is lower, the smaller is the ratio of NH groups to methylene groups in a polyamide. Empirical second moment values at liquid nitrogen temperature and at room temperature, as well as an estimate of theoretical second moment for an assumed sheet model, are reported.