Influence of stereoirregularities on the formation of the gamma-phase in isotactic polypropene

Medium to high molar mass isotactic polypropenes with different amounts of stereoirregularities were characterised with respect to their crystallisati on behaviour and for comparison a random copolymer of ethene and propene wi th 5.8 wt% ethene is used. The influence of stereoregularity and crystallis ation temperature on the gamma -content of the crystallised samples is stud ied by means of wide angle X-ray scattering, atomic force microscopy and li ght microscopy. The paper deals also with the temperature rising elution fr actionation of an iPP with large amounts of stereoirregularities and the in fluence of a nucleation agent on the gamma -content. it is shown that effec ts which render the chainfolding in lamellae more difficult, enhance the fo rmation of the gamma -modification. The necessity of chainfolding in isotac tic polypropene is discussed in terms of a model that is based on the numbe r of chains that emerge from the lamellae surfaces of the alpha- and the ga mma -modification, respectively. (C) 2001 Elsevier Science Ltd. All rights reserved.