Comparative study of the nucleation activity of third-generation sorbitol-based nucleating agents for isotactic polypropylene

The nucleation activity of the sorbitol derivatives 1,2,3,4-bis(3,4-dimethylbenzylidene sorbitol) and methyldibenzylidene sorbitol are compared with that of talc, a conventional nucleating agent for the monoclinic crystalline phase of isotactic polypropylene. The thermal parameters associated with the dynamic crystallization process are studied as a function of the cooling rate by differential scanning calorimetry, and the nucleating efficiency is assessed by comparison with self-nucleation, the highest values being observed for 1,2,3,4-bis(3,4-dimethylbenzylidene sorbitol) over the whole concentration range. The nature of the polymer crystals formed in the nucleated polymer was studied by X-ray diffraction, and the data show an increase in a prefer-red orientation of the polymer crystallites with increasing concentration of nucleating agent, (C) 2002 Wiley Periodicals, Inc.