Conformation Selected Direct Formation of Form I in Isoactic Poly(butene-1)

Though the transition from metastable to stable crystal (from form II to form I) of isotactic poly(butene-1) (iPB-1) after melt crystallization looks to be unavoidable, form I direct formation in bulk iPB-1 via a bypass of form II is still a charming approach to the crystalline structure control in iPB-1. However, the physics behind this transition still remains elusive and there are many arguments. In this work, DSC and WAXS were used to investigate the crystallization behaviors of iPB-1 in detail and direct formation of form I in bulk iPB-1 was found able to occur within a temperature range from the glass transition temperature T _g to a critical temperature T _cr = 35 °C, far below the crystallization temperature T _c of form II. The temperature-dependent 3/1 helix conformation formation within this temperature range was proposed to interpret the further direct formation of form I. Formation of iPB-1 polymorphic structures seem to be controlled by temperature-dependent helix conformation formation. The results may trigger further discussions or shed light on the understanding of the physics behind polymer crystallization and polymorph selection processes as well as the development of crystal structure controlling techniques and applications of iPB-1.