Pulsed n.m.r. studies of the crystallization kinetics of polyethylene from the melt and solution

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Abstract
Pulsed n.m.r. techniques have been used to determine the crystallization rates of polyethylene samples, both commercial polydispersed and monodispersed, in bulk and in approximately 5 % (by mass) solution in tetrachloroethylene. Where comparable, the results agree well with those obtained by Mandelkern (1956)using volume change measurements, but extend his temperature range towards the more rapid crystallization rates. The crystallization-time curves show the existence of an induction period, and a residual amorphous fraction which is lower in solution crystallization. The results agree well with the relation between bulk crystallization rates and degree of supercooling proposed by Mandelkern et al. (1954) provided appropriate melting temperatures,T m , are used. The technique has several advantages for the determination of polymer crystallization rates.