Abstract
The melting and crystallization behaviour of isotactic polypropylene (iPP) in the α ( monoclinic) and γ (triclinic) crystalline modifications has been studied by differential thermal analysis (d.t.a.) under high pressure. The d.t.a. melting thermograms of the sample prepared by slow cooling from the melt at atmospheric pressure (α form) and high pressure (γ form) show single endothermic peaks up to about 4600 bar in isobaric measurements. Two isolated melting point curves, corresponding to the melting of the α and γ modifications, were obtained and the melting points were fitted to a quadratic equation as a function of the pressure (bar). The slope of the curve at atmospheric pressure has been determined accurately for each crystalline form. Two curves were observed for the pressure dependence of the crystallization peak temperature in the d.t.a. curve. The origin of the separated crystallization curves is discussed in relation to the degradation of the iPP melt-crystallized under high pressure.
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