Synthesis of high χ block copolymers with LC moieties and PMMA segments using RAFT polymerization, and their nanostructure morphologies

Abstract

Homopolymers with side-chain liquid crystalline (LC) units were prepared by RAFT polymerization of a new LC monomer, N-(4-dodecylphenyl)-4′-vinylbenzamide. The resulting polymers had low polydispersity, Mw/Mn < 1.2. Optical and thermal investigations confirmed that both the monomer and homopolymers have smectic structures. New diblock copolymers (BCPs) with different ratios of LC monomer, which forms rod-like hard blocks, and methyl methacrylate, which forms coil-like soft blocks, were successfully prepared using RAFT polymerization. We confirmed that polymerization of the block copolymers proceeded with controlled/living characteristics. With a large Flory-Huggins interaction parameter (χ) between the hard and soft blocks and facile formation of LC phases, the new rod-coil BCPs yield highly ordered nanostructures over a large area upon directed self-assembly. Simple solvent annealing of the BCPs produces thin films having in-plane or sphere morphology with long range ordering of 1 μm along the surface of substrate without a guiding template. The observed morphologies were dependent on the composition ratio of the LC hard block to the soft PMMA segment, indicating the role of mesogenic blocks in stabilization of the well-defined nanostructures. Our findings suggest the great potential of new BCPs for nanolithographic pattern formation by directed self-assembly process.