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Conformation Selected Direct Formation of Form I in Isotactic 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 <i>T</i><sub>g</sub> to a critical temperature <i>T</i><sub>cr</sub> = 35 °C, far below the crystallization
temperature <i>T</i><sub>c</sub> 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