Investigation on the fast phase transition mechanism of flow-induced oriented iPB-1

The phase transition mechanism of isotactic polybutene-1 (iPB-1) has always been a central research topic in the fields of polymer physics and industrial application. Phase transition kinetics of the flow-induced oriented form II is significantly faster than the isotropic form II that crystallizes under quiescent condition. In this study, combining the in situ X ray diffraction technique and a homemade extensional rheometer, the influence of amorphous region on the transformation kinetics was been investigated. Results indicated that annealing above the melting temperature (T_m) decreased the phase transition rate, while annealing below the T_m exhibited no obvious impact on the phase transition rate when the annealing time was only 5 min. However, prolonging the annealing time significantly reduced the phase transition kinetics. Remarkably, the crystallinity remained constant during the annealing process, while it exhibited an increase during the subsequent cooling process. The SAXS measurements showed that long spacing decreased after annealing. It is speculated that extended chains in the amorphous region are relaxed and shortened during the annealing process. This work recommends the rapid cooling of iPB-1 products in industrial manufacturing to prevent the relaxation of amorphous chains and promote the phase transition process.