Chain dimension and crystallization temperature affect the II–I transition of isotactic polybutene-1.

Isotactic polybutene-1 (iPB-1) usually crystallizes into form II from the melt first and it then spontaneously transforms into form I with outstanding properties. The mechanism of the well-known II–I transition of iPB-1 is still an open question. In the present paper, the II–I transitions of iPB-1 samples with different molecular weights were explored via differential scanning calorimetry (DSC) and X-ray scattering (SAXS) techniques after crystallization at various temperatures. It was found that the initial and final stages of the transition process depend on the molecular weight of iPB-1. A slower II–I transition rate was observed with increasing molecular weight. The total crystallinity increases significantly in the initial stages of the transition, especially for iPB-1 with high molecular weight, after crystallization at higher temperature. The long spacing, lamellar thickness, and amorphous layer thickness of iPB-1 samples with different molecular weights increase with the isothermal crystallization temperature. The SAXS results indicated that the initial crystal transition rate of iPB-1 increases with the amorphous size after isothermal crystallization at various temperatures. The transition process was discussed and a mechanism is proposed, which is helpful for understanding the transition. [ABSTRACT FROM AUTHOR]