The influence of spacer chain conformations on the nematic ordering of main chain polymers

Abstract

We present a new molecular field theory of the nematic ordering of main chain polymers that allows molecular structure and conformations to be taken explicitly into account. The theory is based on the self-consistency conditions which follow from the invariance of the segmental order parameters with respect to translations along the contour of the polymer. The orientational order parameters of the segments of a polyethylene chain in a nematic medium are calculated and tested with Monte Carlo simulation. The calculations are extended to thermotropic main chain liquid crystalline polymers (LCPs) consisting of rodlike mesogenic units jointed by n-alkane spacers. The temperatures of the nematic–isotropic phase transitions of these LCPs are evaluated for the first time in terms of molecular structure parameters and are contrasted with the temperatures calculated for the respective monomer, dimer and trimer compounds.