Rheology, polymorphic crystal transformation, thermal, and mechanical properties of long‐chain branched isotactic poly(1‐butene)

Abstract

ABSTRACTEffects of long‐chain branches (LCBs) on the rheology, crystal polymorphism, polymorphic transformation, and corresponding thermal and mechanical properties at different crystallization conditions, of isotactic poly(1‐butene) (iPB‐1) are systematically studied. The complex viscosity decreases and tangent increases with the increase of LCB concentration, and they inversely correlate with gels. The low branched samples crystallize into pure Form II by compression molding and cooling the melt to room temperature at a low crystallization cooling rate, whereas the moderate‐to‐highly branched samples crystallize into mixtures of Forms II and III, with a 1–30% fraction of crystals of Form III. The transformation of Form II into Form I in low branched iPB‐1 was not significantly decelerated at different crystallization cooling rates, which is important in thermoforming, foaming, and extrusion blowing processes. Upon heating, Form III in highly branched iPB‐1 with gels does not cold‐crystallize into Form II even at a low heating rate. The low‐to‐highly branched samples mainly in Form I exhibit high yield strength, high melting temperature, and lower ductility, while the highly branched iPB‐1 containing gels and mixtures of Forms I, III, and I′ possess brittleness. Under stretching, Form III predominantly transforms into Form I via a solid–solid crystal transition. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2020, 137, 48411.