Thermotropic main-chain liquid-crystalline photodimerizable poly(vanillylidenealkyloxy alkylphosphate ester)s containing a cyclopentanone moiety

摘要

A new class of main-chain liquid-crystalline photodimerizable vanillylidene-containing alkylpolyphosphate esters were synthesized from 2,5-bis[m-hydroxyalkyloxy(vanillylidene)] cyclopentanones with various alkylphosphoro- dichloridates by solution polycondensation in chloroform at ambient temperature.Their chemical structures were confirmed by FT-IR,~1H,~(13)C and ~(31)P NMR spectroscopic analysis.Dilute-solution viscosity values were measured in order to obtain the intrinsic viscosities of the synthesized polymers.Mesogenic properties and phase behavior were investigated by the use of hot-stage optical polarized microscopy and differential scanning calorimetry.Thermogravimetric analysis revealed that all of the polymers were stable up to 170-230 deg C and decomposed with high char yields.The shorter methylene-chain-containing polymers did not show a liquid-crystalline phase,while the longer methylene-chain- containing polymers showed grainy and nematic textures.The T_g,T_m and T_i values of the polymers decreased with increasing flexible methylene chain length in the polymer backbones.The photocrosslinking properties of the polymers were studied by UV light/UV spectroscopy;the crosslinking proceeds via 2pi-2pi cycloaddition reactions of the vanillylidene exocyclic double bonds of the polymers.The rate of crosslinking was faster for the pendant ethoxy-containing polymers than that of the pendant methoxy-containing polymers.