Topochemical polymerization of dumbbell-shaped diacetylene monomers: relationship between chemical structure, molecular packing structure, and gelation property

Abstract

Herein, we have synthesized novel photopolymerizable dumbbell-shaped diacetylene liquid crystal (LC) monomers by locating a diacetylene dicarboxylic acid group at the center and chemically connecting swallow-tails, such as hydrophobic alkyl chains (abbreviated as AT₃DI) and amphiphilic biphenyl mesogens (abbreviated as BP₃DI), with bisamide groups. Major phase transitions of dumbbell-shaped diacetylene monomers were identified using differential scanning calorimetry (DSC), polarized optical microscopy (POM), and Fourier transform infrared spectroscopy (FT IR). Molecular packing structures were studied based on structure-sensitive wide-angle X-ray diffraction (WAXD) and small-angle X-ray scattering (SAXS) analyses. Mainly, due to nanophase separations and strong intermolecular hydrogen bonding, AT₃DI formed a low-ordered lamellar LC phase at room temperature. BP₃DI self-assembled into highly-ordered crystal phases (K₁ and K₂) at lower temperatures below a low-ordered lamellar LC phase, in which BP₃DI were intercalated with each other to compensate the mutual volume differences. From the photopolymerization of AT₃DI and BP₃DI, it was realized that the topochemical reactions of dumbbell-shaped diacetylene monomers were closely related to their chemical structures as well as molecular packing structures.