Synthesis and self-assembly of coil–rod–coil molecules with lateral methyl and ethyl groups in the center of the rod segment

Abstract

Rod–coil molecules, consisting of a flexible and a rigid block, have a strong capacity to self-assemble into a variety of ordered nanostructures in the bulk state. In this paper, we report the synthesis and characterization of the self-assembly behavior of coil–rod–coil oligomers. These new materials consist of five biphenyls linked together with ether bonds as a rod segment and incorporate lateral methyl or ethyl groups in the center of the rod building block and poly(ethylene oxide) (PEO) with a degree of polymerization (DP) of 7, 12 and 17 coil segments. Structural investigation of these molecules by means of differential scanning calorimetry (DSC) and X-ray scattering (XRD) in the bulk state reveals that side chains, methyl and ethyl groups in the middle of the rod segment, dramatically influence the self assembly behavior in the liquid-crystalline phase. Molecules containing a lateral methyl group based on PEO coil chain (DP of 12 and 17) self-organize into a hexagonally perforated layer (HPL) structure in the liquid- crystalline phase, while the molecule with a lateral ethyl group based on PEO coil chain (DP of 7) self-assembles into a 2-D rectangular columnar liquid-crystal structure. On further increasing of the coil length of the molecule containing ethyl group, the molecules self-organize into a 1-D lamellar structure in the crystalline phase.