Formation and behaviour of low-temperature melting peak of quenched and annealed isotactic polypropylene

The process of low-melting point (LMP) alpha-phase formation in a quenched and annealed isotactic polypropylene (iPP) was studied by means of differential scanning calorimetry. The influence of preparation conditions (quenching and annealing temperatures, annealing times and sample thickness), together with the measurement parameters (heating and cooling rates), on the iPP melting behaviour are analysed. The results reveal a constant yield of LMP crystals over a wide range of quenching temperatures. This study also suggests that the LMP alpha-crystals originate from the crystallization of polymer portions, which are somewhere between the amorphous and the smectic phase on the macromolecular scale of order. (C) 2001 Society of Chemical Industry