Phase transformation in quenched mesomorphic isotactic polypropylene

The transformation of mesomorphic phase to α-monoclinic crystal phase in quenched isotactic polypropylene has been investigated by TEM, DSC and time-resolved SAXS and WAXD methods. It is found that even though the initial appearance of the cluster structure in mesomorphic i-PP seems to support the model of a multi-step process for polymer crystallization, results indicate that the transformation is not spontaneous. In the cluster domains, a significant fraction of chain segments must undergo a reorganization process in order to establish the correct registration of helical hands for crystallization. In addition, a fraction of the ordered chains with correct registration of helical hands should also serve as primary nuclei to initiate crystallization. However, the entire cluster domains should not be considered as ‘precursors’. The growth process via secondary nucleation eventually transforms the cluster structure to the lamellar structure.