MELT TEMPERATURE EFFECTS ON THE POLYMORPHIC BEHAVIOR OF MELT-CRYSTALLIZED POLYPIVALOLACTONE

Experimental evidence is discussed indicating that in the case of poly pivalolactone (PPVL), the time spent in the melt. and the melt tempera ture from which the samples are quenched to the crystallization temper ature, both affect the subsequent crystallization process, and specifi cally the relative proportions of the alpha- and gamma-modifications. Neither thermal degradation nor heterogeneous nucleation by extraneous substances appear to account fully for the observed phenomena. The re sults suggest that the surprising features of the polymorphic behaviou r of PPVL, as reported, may relate to the persistence of structural or ganization, the most likely being nuclei of different crystalline form s, at a temperature which is more than 40-degrees-C above the phenomen ological melting point, i.e. at temperatures comparable to the propose d equilibrium melting temperature of alpha-PPVL.