Influence of main-chain and molecular weight on the phase behaviors of side-chain liquid crystalline polymers without the spacer

Abstract

A series of end-on side-chain liquid crystalline polymers (SCLCPs) based on a biphenyl mesogen, poly(4,4′-alkoxybiphenyl acrylate) (PBiA-m, m = 1, 4, 6, 10, 18), were successfully synthesized by free radical polymerization or reversible addition fragmentation chain transfer (RAFT) polymerization. The chemical structures of the monomers were confirmed by ¹H NMR and mass spectrometry. The phase structures and transition behaviors were studied using DSC, POM and 1D WAXD. The experimental results found that PBiA-m showed the bilayer smectic phase and a higher clearing point (T_i) compared with poly(4,4′-alkoxybiphenyl methacrylate) (PBiMA-m). In addition, poly(4,4′-hexyloxybiphenyl methacrylate) (PBiMA-6) and poly(4,4′-hexyloxybiphenyl acrylate) (PBiA-6) with different molecular weights (M_n) and low molecular weight distributions have been successfully synthesized via the RAFT polymerization. The results indicated that all the polymers exhibited a bilayer smectic phase and T_i increased as the M_n of PBiMA-6 and PBiA-6 increased. Moreover, PBiA-6 had a higher T_i compared with PBiMA-6 with a similar M_n value. All the results suggested that the main-chain (acrylate and methacrylate) and M_n had a great influence on the properties of SCLCPs without the spacer.