CHARACTERIZATION AND PURITY OF SILOXANE SIDE-CHAIN LIQUID-CRYSTALLINEPOLYMERS 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 n umbers of precipitations. Chemical, thermal and dielectric analyses of the products of these precipitations are reported. Continued reprecip itation results in persistent increases in thermal transition temperat ures and differing dielectric spectra, but these changes effectively c ease after six precipitations. The changes are not believed to be due to removal of unsuccessfully grafted residual alkene since no traces o f 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 increa singly narrower molecular weight distribution and higher average molec ular weight. The observed decrease in mobility of the most reprecipita ted samples would be associated with the lower free volume associated with such material.