Properties and molecular self-assembly of liquid crystalline hard–hard diblock and hard–soft–hard triblock copolymers influenced by Flory–Huggins interaction parameter and volume fraction of distinct segments

Abstract

Two series of hybrid liquid crystalline (LC) diblock copolymers (DBCs) and triblock copolymers (TBCs) composed of hard and soft blocks with great control over their molecular masses, dispersities (M_w/M_n = Đ ≤ 1.38) and compositions were prepared via reversible addition-fragmentation chain transfer polymerization in anisole solvent using new p-dodecylphenyl-N-acrylamide monomer, azobisisobutyronitrile initiator, poly(2-[2-(4-cyano-azobenzene-4-oxy)ethylene-oxy]ethyl methacrylate) and poly(2-[2-(4-cyano-azobenzene-4-oxy)ethylene-oxy]ethyl methacrylate)-block-poly(n-butyl methacrylate) macroinitiators. Structures and properties of BCs were characterized by proton nuclear magnetic resonance, gel permeation chromatography, differential scanning calorimeter, optical polarizing microscope, atomic force microscope and grazing-incidence small angle X-ray scattering. Kinetic behavior indicated that block copolymerization proceeded with controlled/living characteristics. Every BCs revealed three endothermic transitions corresponding to glassy phase transition, smectic-to-nematic phase transition (T_S-N) and melting phase transition. DBC-1, DBC-2, TBC-1 and TBC-2 with high-LC volume fractions exhibited strong T_S-N contrasted to DBC-3, DBC-4, TBC-3 and TBC-4 having low-LC contents. DBC-1, DBC-2, DBC-3, TBC-1 and TBC-2 evidenced smectic C structure while TBC-3 containing low-LC segment (39 wt%) showed nematic structure. Morphologies of block copolymer thin films in mixed solvent (Tetrahydrofuran/cyclohexane) vapor annealing system varied significantly, depending on the volume fractions of building blocks and the interactions between the blocks and solvents.