Thermotropic liquid crystalline-cum-photocrosslinkable poly(benzylidene arylphosphate ester)s containing the cyclopentanone moiety

A new class of linear unsaturated polyarylphosphate esters based on dibenzylidene cyclopentanone, possessing liquid crystalline-cum-photocrosslinkable properties has been synthesized from 2,5-bis(m-hydroxyalkyloxybenzylidene)cyclopentanone (m=5,6,8,10) with various aryl phosphorodichloridates (aryl=phenyl, naphthyl, biphenyl) in chloroform at ambient temperature. Their chemical structures were confirmed by FTIR, and 1 H, 13 C and P-31 NMR spectroscopy. Intrinsic viscosity showed that all the polymers were materials of moderate molecular mass. Phase behaviour was investigated with differential scanning calorimetry and hot stage polarizing optical microscopy, under which all the polymers showed anisotropic behaviour. The T-m and T-i of the polymers decreased with the increasing flexible methylene chain in the polymer backbone. The thermal behaviour of the polymers was studied by thermogravimetric analysis, and their photocrosslinking properties investigated by UV spectroscopy. The crosslinking proceeds via 2 pi-2 pi cycloaddition reactions of the dibenzylidene exocyclic double bond of the polymer backbone. The pendant biphenyloxy-containing polymers show faster crosslinking than the pendant naphthyloxy- and phenyloxy-containing polymers. The rate of crosslinking increases as the methylene chain lengthens in the polymer backbone.