SIDE-CHAIN LIQUID-CRYSTALLINE POLYSILOXANES VIA ANIONIC-POLYMERIZATION - (N-UNDECYLOXY)ARENECARBOXYLIC ACID MESOGENS LINKED TO POLY(DIMETHYLSILOXANE-CO-METHYLVINYLSILOXANE)

A novel, anionic route to well-defined side-chain liquid-crystalline p olysiloxanes is described. The usual cationic approach to these polyme rs leads to polydisperse materials with uncontrolled microstructures. Ring-opening polymerization of pentamethylvinylcyclotrisiloxane yielde d a poly-(dimethylsiloxane-co-methylvinylsiloxane) with a low polydisp ersity ((M) over bar(w)/(M) over bar(n)=1.16), a controlled molar mass , and a uniform distribution of pendant vinyl groups along the chain. Vinyl-containing mesogenic molecules could be attached to the polysilo xane vinyl groups in a two-step hydrosilylation reaction by means of t he coupling agent 1,1,3,3-tetramethyldisiloxane, yielding polymers wit h regularly spaced side groups. The flexible disiloxane link increases the mobility of the mesogenic moieties. In this study, 4-(n-undecylox y)benzoic acid and the novel side group 4'-(n-undecyloxy)-4-biphenylca rboxylic acid were used as mesogens. The thermal behavior of the side- chain liquid-crystalline polymers was investigated by means of differe ntial scanning calorimetry and optical microscopy.