High-temperature relaxation promoting form II-to-form I phase transition of Polybutene-1

Abstract

Amorphous coils between crystalline layers of polybutene-1, especially intercrystalline links within, were thought to play a critical role in form I nucleation, but recent experiments found that it actually played a negative role in form II to form I phase transition, that is, obstructing form I growth by hindering translational movements of form II stems. To reexamine the role of amorphous coils, a high molecular weight PB-1 sample was annealed at a high temperature ranging from 40 to 100 °C after low-temperature nucleation. Results indicated that high-temperature annealing after low-temperature nucleation facilitated disentanglement of amorphous coils, promoting subsequent form I growth. The growth rate of form I doubled after relaxation at 100 °C for 5 min. We also explored nucleation mechanism of form I by moving the relaxation process before nucleation of form I. Results indicated that the form I nuclei were highly fragile crystals on the ends of form II lamellae, suggesting critical role of internal stress in form I nucleation. With this study, we assume that the role of amorphous coils in form II to form I phase transition is indispensable. The seemingly conflicting roles of amorphous coils in form I nucleation and growth can be relieved partly by addition of a high-temperature relaxation process. We suggest addition of a high-temperature relaxation process between nucleation and growth to further expedite phase transition in a high molecular weight PB-1 sample. This study is beneficial to further understand form II to form I phase transition.