COLUMNAR MESOPHASE BEHAVIOR OF POLY(DI-N-ALKYLSILOXANE)S

Poly(di-n-alkylsiloxane)s substituted with ethyl up to hexyl side chai ns are capable of forming a columnar mesophase with a nearly hexagonal unit cell. The polymer chains are stretched, but bath the backbone as well as the alkyl side chains are conformationally disordered. The st ability of the mesophase (i.e. its temperature interval) strongly incr eases on going from ethyl to butyl substitution, and remains almost co nstant on going from butyl to hexyl side chains. It decreases upon dec reasing molecular weight of the polymer chains, or if defects are intr oduced into the side chains. Introduction of side chains that facilita te intermolecular dipolar interactions or introduce rigidity stabilize s the columnar mesophase. (C) 1997 Elsevier Science Ltd.