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 polysiloxanes is described. The usual cationic approach to these polymers leads to polydisperse materials with uncontrolled microstructures. Ring-opening polymerization of pentamethylvinylcyclotrisiloxane yielded a poly-(dimethylsiloxane-co-methylvinylsiloxane) with a low polydispersity ((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 polysiloxane vinyl groups in a two-step hydrosilylation reaction by means of the coupling agent 1,1,3,3-tetramethyldisiloxane, yielding polymers with regularly spaced side groups. The flexible disiloxane link increases the mobility of the mesogenic moieties. In this study, 4-(n-undecyloxy)benzoic acid and the novel side group 4'-(n-undecyloxy)-4-biphenylcarboxylic acid were used as mesogens. The thermal behavior of the side-chain liquid-crystalline polymers was investigated by means of differential scanning calorimetry and optical microscopy.