Characterization of side-chain liquid crystal polymers using dynamic mechanical thermal analysis and dielectric thermal analysis

Ten members of a homologous series of side-chain liquid crystal polymers, the poly[[α-(4-methoxybiphenylyl-4′-oxy)-ω-alkyl]methacrylate]s, have been characterized using dynamic mechanical thermal analysis (DMTA) and dielectric thermal analysis (DETA). For the undecyl and dodecyl homologues both techniques revealed a smectic-smectic transition not detected in previous studies either by differential scanning calorimetry or by optical microscopy. It is proposed that this corresponds to a monolayer-bilayer smectic A transition. A weak transition at ca. -30°C is detected using DMTA for polymers with spacer lengths 4-8 and by analogy with poly(methyl methacrylate) may indicate the absorption of small amounts of water. DMTA also proved to be particularly effective in deconvoluting transitions and for the propyl homologue established the existence of a smectic phase suggested by optical microscopy.