Translation and Rotation of Spherulites during the Crystallization of Isotactic Polypropylene with Reduced Chain Entanglements

The isothermal crystallization of isotactic polypropylene (iPP) spherulites was observed under chain entanglements, reduced chain entanglements, and unconfined thick film conditions using polarized optical microscopy (POM). While spherulite translations and rotations were not observed in entangled iPP samples, the growing spherulites in the entanglements-reduced crystallizing melt conspicuously translated and/or rotated, even when their sizes exceeded the sample film thicknesses. Our entanglements-reduced samples were prepared by first slowly crystallizing a commercial entangled iPP in mineral oil (and then extracting the mineral oil with hexane) and by a direct polymerization method, respectively. The purity of the entanglements-reduced iPP samples and the extent of chain entanglements were examined by thermogravimetric analysis (TGA), gel permeation chromatography (GPC), and rheological measurements. Our findings seem to provide new clues into the crystallization of high molecular mass polymers.