Direct Formation of Isotactic Poly(1-butene) Form I Crystal from Memorized Ordered Melt

TLDR

Unlike a disordered melt that crystallizes directly into form II, the memorized ordered melt of isotactic polybutene‑1 can recover form I upon cooling. The study investigates crystallization from memorized ordered melt of isotactic polybutene‑1 using in‑situ FTIR microspectroscopic imaging and wide‑ and small‑angle X‑ray scattering. Recovery of form I is attributed to the memorized ordered melt, which preserves the conformation order of form I and remains stable at high temperature, acting as a partially ordered layer at the crystal–melt interface. After partial melting, a small fraction of form I crystals reappears upon cooling, with the memorized ordered melt associating with preserved form I, occupying only a minor portion of the melt, and localizing at the crystal–melt boundary—behavior consistent with nonclassical nucleation and growth theory.

Abstract

Crystallization from memorized ordered melt (MOM) of isotactic polybutene-1 (iPB-1) is investigated with in situ Fourier transformation infrared microspectroscopic imaging and wide- and small-angle X-ray scattering. After being partially melted at high temperature, a small portion of form I crystal of iPB-1 recovers back when the temperature is lowered. This is different from a disordered melt, which crystallizes into form II directly. The recovery of form I crystal is attributed to the presence of MOM, which may keep the conformation order of form I crystal. Experimental evidence show that MOM possesses three characteristics, namely: (i) associating with the preserved form I; (ii) occupying only a small portion of the melt in the partially melted sample; (iii) being stable at high temperature. All this experimental evidence suggests that MOM locates at the boundary of crystal and melt. This is in line with the physical picture of nonclassical nucleation and growth theory or the multistage approach, where a partially ordered melt layer locates at the boundary of crystal and melt.