Re-entrant isotropic phase in a supramolecular disc-like oligomer of 4-[3,4,5-tris(n-dodecanyloxy)benzoyloxy]-4′-[(2-vinyloxy)ethoxy]biphenyl

Abstract

The synthesis of 4-[3,4,5-tris(n-dodecanyioxy)benzoyloxy]-4′-[(2-vinyloxy)ethoxy]biphenyl (7), its cationic polymerization to poly{4-[3,4,5-tris(n-dodecanyloxy)benzoyloxy]-4′-[(2-vinyloxy)ethoxy]biphenyl}(8) with narrow molecular-weight distribution (M_w/M_n⩽ 1.25) and relative number-average degrees of polymerization (DP) from 2.7 to 8, and the characterization of the resulting oligomers by a combination of techniques consisting of differential scanning calorimetry, thermal optical polarized microscopy, and X-ray scattering experiments are presented. Compound 8 with DP = 3.2–3.9 displays a crystalline phase and a columnar hexagonal (Φ_h) mesophase at higher temperatures. Compound 8 with DP ≈ 5 exhibits a Φ_h mesophase and a thermodynamically stable enantiotropic re-entrant isotropic (I_re) phase. Compound 8 with DP > 5 is isotropic. The phase behaviour of the oligomers is explained based on the self-assembling of the tapered structural units of 8 into a supramolecular disc-like architecture in which the polymer backbone is confined to the centre of the disc-like supramolecule. The disc-like supramolecular architectures are responsible for the generation of Φ_h, I_re, and isotropic phases. Various structural suggestions for the influence of the molecular weight of 8 on its phase behaviour are discussed.