Synthesis and properties of novel photocrosslinkable aromatic-aliphatic liquid crystal copolyesters based on poly(ethylene glycol) and cinnamic acid

Firstly, PEGn-TA monomers with carboxyl functional groups were synthesised by terephthalic acid (TA) and poly(ethylene glycol) (PEG) with molecular weight of 200, 400 and 600. Then, photocrosslinkable thermotropic liquid crystal copolyesters derived from PEGn-TA, 4,4ʹ-biphenol, 4-hydroxy-cinnamic acid and 4-hydroxy-benzoic acid were successfully obtained by Vilsmeier adduct solution polymerisation method. Influence of PEG molecular weight on thermal behaviour, liquid crystal mesophase, hydrophilicity, structure and photoactivity were investigated by various measurements. Experimental results indicated that all copolyesters showed nematic mesophase textures, relative low melting temperatures, and two glass transitions as well as better hydrophilicity were observed for those contained higher PEG molecular weight. Photocrosslinking rate was increased first and then decreased due to effect of flexible PEG moieties. The resulted copolyesters with liquid crystal behaviour, excellent hydrophilicity and photoactivity could be potentially used as biomaterial.