Effects of nucleating agents on the II–I transition of iPB-1

Abstract

For isotactic polybutene-1 (iPB-1), II–I transition is of great industrial importance; however, the traditional nucleation-controlled solid–solid II–I transition mechanism eventually encountered challenges and the roles of iPB-1 amorphous phase gained the interest of many researchers. With three nucleating agents, namely WBQ-88, TMB-5 and WBG-II, incorporated into iPB-1, the amorphous phase was tuned with a form II crystalline structure remaining fixed. Based on the observed T_m,II decrease and T_m,I increase during the II–I transition as well as the resulting final T_m,I synergistically tuned by nucleating agent incorporation and crystallization conditions, it is proposed that the entire II–I transition of iPB-1 involves a form II consumption process and a form I formation process. The same as-crystallized form II structures of iPB-1 containing various nucleating agents are involved in a fixed form II consumption process. The amount of iPB-1 chain segments in the amorphous phase, which have the ability to crystallize, as well as their actual ability to crystallize synergistically determine the initiation of form I crystallization. Consequently, the started form I crystallization triggers II–I transition by overcoming the energy barrier for form II crystal cells to be destroyed. Both the initiation and the subsequent form I crystallization process can be enhanced by nucleating agent incorporation or isothermal crystallization at different T_c values, comprehensively resulting in a fast II–I transition process with final form I crystalline structures determined. The results provide an understanding of the II–I transition mechanism and shed light on the development of techniques to accelerate the II–I transition for iPB-1 industrial applications.