Purity of liquid‐crystal polysiloxanes, 1. Isolation procedures

The removal of the alkene side‐chain precursor from liquid‐crystal (1.c.) polysiloxanes during their isolation by precipitation has been monitored by thin‐layer chromatography. The commonly used procedure involving only three precipitations has been shown to be frequently insufficient to remove the alkene completely from the 1.c. polymer. Using 8 to 10 precipitations and monitoring the removal of alkene to <0,1 wt.‐%, the resultant polymers have been found to have both higher glass transition temperatures and higher clearing temperatures; more consistent phase transition temperatures are also obtained from batch to batch.