Synthesis And Self-assembly Of PCBOA Side-Chain Liquid Crystalline Block Copolymers

Liquid crystalline block copolymers(LCBCs)have been extensively studied in recent years owing to their organization at different scales with hierarchical structures,and the interplay between the LC ordering and the microphase-separated domain morphologies attracts great interest.We focus here on the synthesis and self-assembly of PCBOA LCBCs.The details are as follows:(1)A series of narrowly distributed diblock copolymers composed of amorphous components and side-chain LC:poly(butyl acrylate)-block-poly[8-(4'-cyano-4-biphenyl)-1-octanoyl acrylate](PBA-b-PCBOA),with LC block weight fraction(f_w,PCBOA)ranging from 25%to 87%,were synthesized by atom transfer radical polymerization(ATRP).GPC results show that all polymers have narrow PDI,and ¹H NMR results prove of the detailed structure and molecular weights of diblock copolymers.DSC and POM results show that in two series of samples,the isotropization temperatures decrease with the decrease of LC content.The SAXS and AFM results reveal the diblock copolymers with different compositions 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-coating thin film,the lamella phase separation domain size decreases with increasing annealing time.On the other hand,at lower cooling rate,the lamellar morphology with smaller domain size is observed.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.(2)The triblock copolymers containing two different liquid crystalline polymers,poly(butyl acrylate)-block-poly[8-(4-cyano-4'-biphenyl)-1-octanoyl acrylate]-block-poly(2,5-bis-[4-methoxyphenyl]oxycarbonyl)styrene)(PBA-b-PCBOA-b-PMPCS)are synthesized through three ATRP steps.The structure of the block copolymers are characterized by GPC and ¹H NMR.The liquid crystalline properties of triblock copolymers are roughly studied by DSC and POM.