Role of amorphous phase in II-I transition of iPB-1/iPP blends

Isotactic polybutene-1 (iPB-1) possesses excellent physical and mechanical properties, but its applications are limited owing to the slow II-I transition after melt processing. The concerned II-I transition mechanism is a long-lasting hot topic. After an isotactic polypropylene (iPP) was melt-blended into iPB-1, a good model system for II-I transition study to discuss on roles of amorphous phase was consequently obtained with amorphous phase tuned but form II crystalline structures almost kept fixed according to the affected crystallization and melting behaviors of iPB-1 in iPB-1/iPP blends. Both DSC and FTIR results revealed the enhanced II-I transition behaviors of iPB-1 in the blends and FTIR results especially confirmed form I direct crystallization from amorphous phase of iPB-1/iPP blends prior to form II consumption due to II-I transition. The earlier the direct form I crystallization, the faster II-I transition of iPB-1 in the iPB-1/iPP blends. It was proposed that form I direct crystallization of the iPB-1 chain segments which have ability to crystallize but remained in the amorphous phase lowered the energy barrier of transition from adjacent form II crystals to packed-mesophases due to the local volume contract resulting in a stretch to iPB-1 chains with parts contained in the adjacent form II crystals. Consequently, the II-I transition of adjacent form II crystals were triggered to start and it generated a ripple effect on the entire II-I transition process. The results are of great significance on understanding of iPB-1 II-I transition process and also of importance for iPB-1 industrial applications.