Promoting Form II-Form I Phase Transition of Polybutene-1 by Constantly Alternative Annealing

The slow phase transition from form II to form I has always been an important factor that restricts the processing and application of polybutene-1 (PB-1). After extensive efforts, a set of effective methods for promoting the phase transition rate in PB-1 was established by adjusting the crystallization, nucleation, and growth temperatures. Nevertheless, low-molecular-weight PB-1 (LMWPB-1) faces challenges because this method requires a low crystallization temperature, which is difficult to achieve during extrusion processing. In this study, we attempted to increase the phase transition rate in PB-1 by changing the annealing temperature after processing rather than the crystallization temperature in the classical scheme. The results indicated that regardless of low- or high-molecular-weight PB-1, repeated annealing between 0 and 90 oC could also promote form II to form I phase transition. The initial content of form I increased with the heating and cooling cycles. The half-time of the phase transition (t_1/2) was also shortened after heating/cooling. After 100 heating/cooling cycles, t_1/2 was reduced to one-quarter of that without annealing, which had almost the same effect as the crystallization temperature at 25 °C in promoting the phase transition. This study indicates that annealing after processing is also an important factor affecting the phase transition of PB-1, and should receive sufficient attention.