Recent Studies On β-Crystalline Form Of Isotactic Polypropylene

Isotactic polypropylene shows four distinguishable chain conformation with each being a 2 × 1/3 helix1. Different packing geometries lead to three well known crystalline structures (polymorphs), namely the monoclinic α-form, the hexagonal β-form and the triclinic γ-form. The appearance of these structures is critically dependent upon the ciystallization conditions1–5. Among these three crystalline structures, the monoclinic α-form is by far the most common, being found in normal melt-crystallized or solution-crystallized IPP samples. In the industrial practice, therefore, β- and γ-form have been considered as laboratory curiosities2. The practical way for obtaining β-form with relative high purity is to use nucleating agent. Only a few materials are known to nucleate β-form spherulites6,7.