The crystallization of polypropylene with reduced density of entanglements Part B Polymer physics

The crystallization of polypropylene with different density of macromolecular entanglements was studied in isothermal and non‐isothermal conditions. The growth rate of spherulites increased with reduced concentration of entanglements. Reduction of entanglements shifted the temperature of transition between Regimes II and III, which means that more regular growth of crystals was possible at lower temperature. The range of temperatures at which polypropylene cavitated in regions of melt occluded by spherulites was limited to 137–139°C, with weak dependence on entanglements density. DSC studies showed that isothermal crystallization is faster in less entangled polymers, however the crystallinity degree and long period of structure (by SAXS) were similar for studied materials. When the crystallization was completed during fast cooling, the differences between individual samples were more significant. The partial disentangling, overcoming some limitation for movements of macromolecules, made possible easier crystallization, even at low temperature of Regime III. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 748–756