Thermal Properties and Liquid Crystal Phase Behaviors of Well-Synthesized Terphenyl Polyacrylates with Two Alkoxy Tails and Varied Length Alkyl Spacers

Abstract

Side-chain liquid crystalline polymers (SCLCPs) with terphenyl-based side groups have been rarely reported, mainly due to the severe challenge of poor solubility resulting from the ultrastrong π-interactions between the terphenyl aromatic moieties. Herein, a series of terphenyl polyacrylates SCLCPs with ortho- or meta-disubstituted alkoxy tails and varied length alkyl spacers have been synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. For the ortho-disubstituted series side-chain polymers of P(o,6,6)-t with two hexyloxy tails and increased t-methylene alkyl spacer of t = 2, 4, 6, 8, 10, enantiotropic SmC and SmA mesophases are formed, with a gradual increase in SmC to SmA transition temperatures and decrease in clearing temperatures, which is ascribed to the spacer decoupling effect and the enhanced internal plasticization of the elongated alkyl spacers. In addition to exhibiting the enantiotropic SmA and SmC mesophases, P(o,10,10)-6 with two longer decyloxy tails exhibits a SmC phase with an unexpected layer spacing increase at lower temperatures due to partial crystallization of the longer alkyl tails. For the meta-disubstituted side-chain polymers bearing two hexyloxy tails, P(m,6,6)-2 and P(m,6,6)-6 with shorter alkyl spacers generate a poorly developed SmA phase, P(m,6,6)-10 with a longer ten-methylene spacer forms a less developed undulated lamellar phase. This study demonstrates the realization of SCLCPs with terphenyl-like mesogens of ultrastrong π-interactions by controlled polymerization and provides valuable insights into their phase transitions and hierarchical structure organization.