THE INFLUENCE OF SPACER CHAIN CONFORMATIONS ON THE NEMATIC ORDERING OF MAIN-CHAIN POLYMERS

We present a new molecular field theory of the nematic ordering of mai n chain polymers that allows molecular structure and conformations to be taken explicitly into account. The theory is based on the self-cons istency conditions which follow from the invariance of the segmental o rder parameters with respect to translations along the contour of the polymer. The orientational order parameters of the segments of a polye thylene 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 mesogen ic 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 wit h the temperatures calculated for the respective monomer, dimer and tr imer compounds. (C) 1996 American Institute of Physics.