Synthesis and dielectric properties of novel liquid crystalline triblock copolymers with cyanobiphenyl moieties and poly(n-butyl acrylate) segments

Abstract

In this work, self-assembly method was used to improve the dielectric constant of triblock copolymers. A series of ABA triblock copolymers with a defined length of poly(n-butyl acrylate) (PBA, B block) segment and different lengths of liquid crystalline (LC) poly[11-(4-cyano-4′-biphenoxy)undecyl methacrylate] (P11CBMA, A block) segments were synthesized by using the atom transfer radical polymerization method. The well-defined triblock copolymers P11CBMAm-b-PBAn-b-P11CBMAm possess three different B/A ratios (n=50, m=17, 43, 53). Due to the supramolecular cooperative motion effect, the copolymers can form worm-like microstructure (WLC=52.8%), cylinder-like nanostructure with P11CBMA phase embedded in PBA matrix (WLC=73.9%), and wide stripe structure with LC domains distributed unevenly in a continuous PBA matrix (WLC=77.7%) after annealed at 160°C (above Ti) under N2 for 24h, respectively. In order to study the influence of microphase separated morphology of triblock copolymer on the dielectric properties, solvent annealing was also used to develop various nanostructures. After thermal or solvent annealing, the dielectric constants of block copolymers increased dramatically while their loss factors remained the same. For different block copolymers, the dielectric constants increased with the increase of the LC block length. For diverse treatments, dielectric permittivities of samples varied widely with different nanostructures. The results show that the dielectric constants of block copolymers could be tuned by the block ratios and the self-assembled microstructures. These findings will inspire researchers using self-assembly method to design and develop novel flexible materials with high dielectric permittivity. © 2014 John Wiley & Sons, Ltd.