beta-modification of isotactic polypropylene: Preparation, structure, processing, properties, and application

The methods of preparation and formation of supermolecular structures in quiescent and sheared melts and the properties of the beta-modification of isotactic polypropylene (beta-iPP) are reviewed. The introduction of selective beta-nucleants is the most reliable method for preparation of samples rich in beta-modification or of pure beta-iPP. The advantages and drawbacks of the known beta-nucleating agents are summarized. It is emphasized that pure beta-iPP can be prepared under laboratory and processing conditions in the presence of highly active and selective beta-nucleants. Nevertheless, there are no literature data-apart from that of the author's groups-which evidenced unambiguously the formation of pure beta-iff. It hints at the insufficient selectivity of beta-nucleants used or at the inappropriate crystallization or melting conditions applied by other scientists. The structure formation during the high-temperature hedritic crystallization is discussed comprehensively and illustrated by polarized light microscopy and scanning electron microscopy micrographs. Some specific features of beta-iPP, namely the high- and low-temperature growth transition, the restricted temperature range of the formation of pure beta-iPP, and the unique melting and recrystallization characteristics (melting and annealing memory effect) are summarized. It was emphasized that impact strength and toughness of beta-iPP markedly exceed those of alpha-iPP. Processing of beta-nucleated iPP and application of beta-nucleated iPP is described briefly.