Characterisation and purity of siloxane side-chain liquid-crystalline polymers by gel-permeation chromatography and dielectric relaxation spectroscopy

A number of siloxane-based side-chain liquid-crystalline polymers have been synthesized and subjected to purification involving increasing numbers of precipitations. Chemical, thermal and dielectric analyses of the products of these precipitations are reported. Continued reprecipitation results in persistent increases in thermal transition temperatures and differing dielectric spectra, but these changes effectively cease after six precipitations. The changes are not believed to be due to removal of unsuccessfully grafted residual alkene since no traces of alkene could be detected chemically after even three precipitations. A possible explanation for continuing changes for greater than three precipitations could be that repeated precipitation leads to an increasingly narrower molecular weight distribution and higher average molecular weight. The observed decrease in mobility of the most reprecipitated samples would be associated with the lower free volume associated with such material.