Polymerization-induced self-assembly of liquid crystalline ABC triblock copolymers with long solvophilic chains

Abstract

Understanding the self-assembly of liquid crystalline (LC) block copolymers is challenging because of the complex influencing factors. In this article, we studied the influence of the solvophilic chain length on the self-assembly of the LC ABC triblock copolymer poly(N,N-dimethylaminoethyl methacrylate)-b-poly(benzyl methacrylate)-b-poly[2-(perfluorooctyl)ethyl methacrylate] (PDMA-b-PBzMA-b-PFOEMA) by polymerization-induced self-assembly, where PFOEMA served as the LC block. PDMA₇₂ was used for preparing PDMA-b-PBzMA spheres with varying sizes, which were subsequently used as seeds for mediating the seeded reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of FOEMA to target PDMA-b-PBzMA-b-PFOEMA assemblies. By regulating the degree of polymerization (DP) of PBzMA and PFOEMA, a range of morphologies, including spheroids, cylinders, and spherical multicompartment micelles (MCMs), were achieved. The morphology evolution of these assemblies was further investigated by transmission electron microscopy, small angle X-ray scattering, and differential scanning calorimetry, which revealed that together with the microphase segregation of PBzMA/PFOEMA, the interchain repulsion of PDMA competes with the LC anisotropic ordering of the PFOEMA block, thus dictating the morphology of PDMA-b-PBzMA-b-PFOEMA assemblies. When the DP of PBzMA is low, LC anisotropic ordering of PFOEMA predominates, and therefore ellipsoids and cylinders are generated. When the DP of PBzMA is high enough, the microphase segregation would impair the LC anisotropic ordering of PFOEMA, hence affording spherical MCMs, where the interchain repulsion of PDMA favors a spherical shape, and the microphase segregation of PBzMA/PFOEMA results in a multicompartmental nanostructure of the micellar core. Our study thus demonstrated the influence of interchain repulsion of the solvophilic block, the microphase segregation and the LC ordering of the solvophobic blocks on the self-assembly of LC copolymers, which would be beneficial for designing LC assemblies as drug carriers and nano-actuators.