Synthesis and characterization of photo-crosslinkable liquid crystalline copolyesters containing arylidene-keto and chalcone moieties

A series of six photo-crosslinkable thermotropic liquid crystalline copolyesters were prepared by polycondensation method at room temperature using tetra-n-butylammonium bromide as the phase transfer catalyst. The diacid chloride involved in this process was adipoyl chloride, the common diol (diol-1), also referred to as bischalcone diol, used was 3,3′-benzene-1,4-diylbis[1-(4-hydroxyphenyl)prop-2-en-1-one] and six different arylidene diols were involved as varying diols (diol-2), in the ratio 2:1:1. The common diol and the six arylidene diols were synthesized by the acid-catalyzed Claisen-Schmidt synthesis. The inherent viscosity η_inh of these six copolyesters was found between 0.35 and 0.45. The microstructure of the repeating unit present in the copolyester chain was confirmed by FT-IR, ¹H–NMR and ¹³C–NMR spectroscopic techniques. Thermal transition temperatures, resolved from the DSC thermograms, were found to be well above room temperature. Optical polarizing microscopy was employed to establish the liquid crystalline property and all the polymers were found to have nematic phase. The photo-crosslinking behaviour of these copolyesters was studied in DMF solution at different time intervals. The copolyesters having methoxy group in them absorb UV-A rays (315–400 nm) for a longer duration, which promotes them to be good candidates for UV filters and sunscreens.