Solid State Phase Transitions in Poly(ethylene oxide) Crystals Induced by Designed Chain Defects

Abstract

We have used Cu(I)-catalyzed azide–alkyne cycloaddition to synthesize a new series of poly(ethylene oxide)s having in the center of their chains two 1,2,3-triazole (TR) rings separated by (CH2)n spacers with 2 ≤ n ≤ 4 (PEO11-TR-(CH2)n-TR-PEO11). The degree of crystallinity obtained by temperature-dependent WAXS measurements indicates that only one out of the two PEO11 chains of the three polymers forms a 72 helix upon cooling to −10 °C and crystallizes into a monoclinic unit cell known from PEO homopolymer. A solid-state phase transition occurs for all samples during heating below their melting temperature. Solid-state 13C MAS cross-polarization and single-pulse NMR spectroscopy indicate the complete incorporation of the chain defects into the PEO crystals (PEO-TR phase) during this transition. The 2D WAXS pattern of an oriented PEO11-TR-(CH2)2-TR-PEO11 sample generates a structural model where the crystal lattice of the initial PEO phase becomes highly distorted during the solid-state phase transition du...