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

Abstract

Effects 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 0 possess brittleness. Under stretching, Form III predominantly transforms into Form I via a solid-solid crystal transition.

Research on the 2-Chloro-4-amino-6,7-dimethoxyquinazoline Solubility in 12 Monosolvents at Various Temperatures: Experimental Measurement and Thermodynamic Correlation

“…In addition, the relative stability of polymorphs of drugs depends on free energies. Such a polymorphic transformation is often detrimental to the efficacy of the formulation. , The extent of polymorphic transition depends on the processing conditions and the relative stability of the polymorphs. The same infrared absorption peaks and intensity could be used to prove that there is no crystal transition and polymorphic transformation of the solute.…”