Influence of microstructure and semi-crystalline morphology on the β and γ relaxations of the metallocene isotactic polypropylene

In this work, the characteristics of the beta and gamma mechanical relaxations, i.e., temperature and relative intensity, of a series of metallocene iPP samples (MPP) are analysed. The hypothesis that the temperature and the intensity of the glass transition (beta relaxation) and local sub-T(g) motions (gamma relaxation) are related mainly to chain parameters and morphology has been corroborated. On the one hand, it has been found a critical average isotactic length (n(1)) around 30 propylene units, under which the beta and gamma dynamics are promoted with respect to the alpha relaxation. On the other hand, it is apparent that the features which determine the degree of constraint within the inter-lamellar region, i.e., the fraction of low-T(m) crystals. drive the relative intensities of the alpha, beta and gamma relaxation processes.