Molecular simulation and experimental characterisation of monotropic and enantiotropic polymers containing azobenzene and diphenyl mesogens

Abstract

Molecular simulation techniques have been applied to previously synthesised liquid crystalline polymers containing azobenzene and diphenyl mesogenic groups within the chain. Single chains and amorphous unit cells of aromatic polymers with a degree of polymerisation of 4–16 and containing propylene and diethyletheric (oxydiethylene) spacers were used. The energy was minimised and then molecular dynamics were performed for 1000 ps at seven temperatures between 10 and 600 K. The axial ratio or coefficient of asymmetry was calculated from computer-generated structures. The predictive capability of the orientational order parameter was used to estimate the degree of orientation and the liquid crystalline–isotropic transition temperature of the polymers. The simulated results for the monotropic polymers agreed very well with Maier–Saupe mean field theory and experimental data, though the enantiotropic polymer did not show a good agreement. The predicted glass transition and decomposition temperatures of the simulated polymers are also reported.