Influence of Molecular Weight on Phase Transition Entropies of a Thermotropic Nematic Polyester

Abstract

We report the values of isotropisation enthalpies and entropies of some model compounds, oligomers, and polymers of poly(2,2′-methyl-4,4′-oxyazoxybenzene dodecanedioyl), a thermo-tropic nematic polymer with moderately low transition temperatures and regularly alternating rigid-flexible units in the main chain. The values of ΔH_IN and Δ_IN increase rapidly with increasing molecular weight, to reach a plateau at M _n > 3,000 g/mole. Results are interpreted in terms of increasing participation of the flexible aliphatic spacer units in the ordering process of the nematic phase. In the polymer, the entire repeating unit is aligned by the nematic potential.