Influence of liquid crystalline formation on the phase behavior of side-chain liquid crystalline block copolymers

A series of narrowly distributed diblock copolymers composed of amorphous components and side-chain liquid crystalline (LC) polymer, poly (butyl acrylate)-block-poly [8-(4-cyano-4'-biphenyl)-1-octanoyl acrylate] (PBA-b-PCBOA), with side-chain LC block weight fraction (f(w,PCBOA)) ranging from 25% to 87%, were synthesized by atom transfer radical polymerization (ATRP). Their thermal property, LC behavior, bulk phase behavior and thin film morphology were studied by differential scanning calorimetry (DSC), polarizing optical microscope (POM), small-angle X-ray scattering (SAXS) techniques and atomic force microscopy (AFM), respectively. The results show the diblock copolymers with different composition could present sphere, lamellar and cylinder morphologies before the order disorder transition. As the mesogen units self-organize to form smectic phase, the lamellar morphology dominates during the majority LC block weight fraction range (f(w,PCBOA) = 46%-77%) to minimized the surface energy. Interestingly, for spin-coated thin film, the lamella phase separation size decreased with increasing annealing time. For the copolymer with f(w,PCBOA) of 67%, a thermoreversible order order transition (OOT) and lamella to lamella/modified layer (L/ML), were observed. (C) 2015 Elsevier Ltd. All rights reserved.