The Shear-Accelerated II-I Phase Transition of Isotactic Poly(1-Butene)

The II-I phase transition of isotactic poly(1-butene) (iPBu) leads to improved mechanical performance. However, this will take several weeks and increase storage and processing costs. In this work, shear forces are introduced into the supercooled iPBu melt, and the effects of isothermal crystallization temperature (T_c) and shear temperature (T_shear) on crystallization and phase transition are explored. Shear-induced transcrystalline morphology of Form II with a significantly shortened crystallization induction period can be observed at relatively high T_c (105 °C). Besides, the shear-induced Form II can transit to Form I faster than the unsheared one. In addition, the phase transition rate increases as the T_shear decreases, with the fastest rate occurring at T_shear of 120 °C. The half transition time (t_1/2) is measured as 6.3 h when T_c = 105 °C, T_shear = 120 °C, which is much shorter than the 20.7 h required for unsheared samples. The accelerated phase transition of iPBu can be attributed to the stretching of molecular chains, resulting from shear treatment. This study provides a quantitative analysis of the influence of the shear treatment and the T_shear on the II-I phase transition rate. It also presents a cost-effective and straightforward approach for expediting the phase transition process.