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

Experimental evidence is discussed indicating that in the case of polypivalolactone (PPVL), the time spent in the melt. and the melt temperature from which the samples are quenched to the crystallization temperature, both affect the subsequent crystallization process, and specifically 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 results suggest that the surprising features of the polymorphic behaviour of PPVL, as reported, may relate to the persistence of structural organization, the most likely being nuclei of different crystalline forms, at a temperature which is more than 40-degrees-C above the phenomenological melting point, i.e. at temperatures comparable to the proposed equilibrium melting temperature of alpha-PPVL.