Self-assembly of coil-rod-coil triblock copolymers depending on lateral methyl groups at the interface of rod and coil segments

Triblock coil-rod-coil compounds, consisting of four biphenyls and a p-terphenyl unit linked together with ether bonds as a rod segment, incorporating lateral methyl or ethoxymethyl groups at 2 and 5 positions of the benzene ring of p-terphenyl and poly(ethylene oxide) (PEO) with a degree of polymerization of 7, 12, 17, incorporating lateral methyl groups between the rod and coil segment as the coil segments, were synthesized. The compound structures were characterized with H-1 NMR and matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) mass spectroscopy. The self-assembling behavior of the compounds is investigated by means of differential scanning calorimetry (DSC), small-angle X-ray scattering (SAXS), and optical polarized micrograph (POM) in the bulk state. These compounds spontaneously self-assemble into lamellar, hexagonal perforated lamellar, rectangular columnar, and oblique columnar structures in the crystalline phase, and hexagonal perforated lamellar, bicontinuous cubic, and oblique columnar structures in the liquid crystalline phase, respectively. The results revealed that the lateral methyl groups attached to the interface of rod and coil segments strongly induce the compounds to self-assemble into various supramolecular nanostructures in the crystalline phase and the liquid crystalline mesophase.