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 (Ti) 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 (Mn) 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 Ti increased as the Mn of PBiMA-6 and PBiA-6 increased. Moreover, PBiA-6 had a higher Ti compared with PBiMA-6 with a similar Mn value. All the results suggested that the main-chain (acrylate and methacrylate) and Mn had a great influence on the properties of SCLCPs without the spacer.