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

Abstract

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.

An FTIR and X‐ray diffraction study of the crystal phase transition in isotactic polybutene‐1

“…The direct formation of the form I from the melt of iPB‐1 has been reported by DSC characterization together with the thermal history of heating and cooling 39–41 . However, only thermal not structural properties can be obtained from such measurements.…”

Effect of an additive TAB-1 on crystallization behaviors and tensile properties of iPB-1

“…Both the T g and the T m values here were determined by differential scanning calorimetry (DSC) and the adopted heating rate is 10 °C min −1 . 52 An additive (trade name TAB-1) which can accelerate the II-I transition of iPB-1 as previously reported 51 was obtained from Weihai Ultron PolyMater Technology Co., Ltd., China.…”

“…The prior chain segmental conformation adjustment and selection are crucial to melt crystallization and polymorph selection of a polymorphic polymer melt. 39,50,52 The adjustment of the chain conformation of iPB-1 tends to be more difficult during melt crystallization relative to that of polyethylene and polypropylene due to the large side ethyl groups of iPB-1 which results in larger entropic barriers of melt crystallization. The iPB-1 melt is a strong rather than a fragile liquid.…”

Thermomechanical properties of poly(1‐butene) synthesized by Ziegler–Natta catalyzed polymerization of 1‐butene in the presence of nucleating agents

“…1 Form II produced spontaneously on bulk crystallization has an 11 3 helix geometry and a tetragonal unit cell. Form I which is isostructural with form I 0 has a 3 1 helix geometry and a trigonal unit cell, and it is obtained by spontaneous crystal-crystal transformation of form II on aging, [36][37][38] whereas form I 0 is produced by direct crystallization. Form III, produced only from dilute solution, has a 4 1 helix conformation and an orthorhombic cell geometry.…”