Linear Rod−Coil Multiblock Oligomers with a Repeating Unit-Dependent Supramolecular Organization

Abstract

A series of linear rod−coil multiblock oligomers of the (rod−coil)n type (n = 1, 2, 3, 13) consisting of a rigid rod segment made up of three biphenyls connected though methylene ether linkages and a poly(propylene oxide) with degree of polymerization of 13 as a coil segment were prepared, and their thermal behavior and supramolecular organization in the solid and melt states were investigated. In opposition to the behavior of conventional oligomers, transition temperatures of these multiblock oligomers associated with both crystalline melting and isotropization decrease with increasing the number of repeating units (n). Small- and wide-angle X-ray diffraction investigations were carried out to elucidate the details of supramolecular structure. All of the oligomers were observed to be self-organized into ordered supramolecular structures that differ significantly on variation of the number of repeating units. The (rod−coil)1 shows a lamellar crystalline and a bicontinuous cubic liquid crystalline structures. In contrast, the (rod−coil)2 shows a 2-D rectangular crystalline and a tetragonal columnar liquid crystalline structures, while the (rod−coil)3 and the (rod−coil)13 display a hexagonal columnar structure in both their solid and melt states. These results demonstrate that systematic variation of the number of repeating units in the rod−coil multiblock oligomers can provide a strategy to regulate the supramolecular structure, from 1-dimensional lamellar, 2-dimensional rectangular to 2-dimensional hexagonal structures in the solid state and from bicontinuous cubic, tetragonal columnar to hexagonal columnar in the melt state.