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

Medium to high molar mass isotactic polypropenes with different amounts of stereoirregularities were characterised with respect to their crystallisation behaviour and for comparison a random copolymer of ethene and propene with 5.8 wt% ethene is used. The influence of stereoregularity and crystallisation temperature on the γ-content of the crystallised samples is studied by means of wide angle X-ray scattering, atomic force microscopy and light microscopy. The paper deals also with the temperature rising elution fractionation of an i-PP with large amounts of stereoirregularities and the influence of a nucleation agent on the γ-content. It is shown that effects which render the chainfolding in lamellae more difficult, enhance the formation of the γ-modification. The necessity of chainfolding in isotactic polypropene is discussed in terms of a model that is based on the number of chains that emerge from the lamellae surfaces of the α- and the γ-modification, respectively.