Chain stiffness of liquid crystalline polyesters. 1. Characteristic ratio and persistence length

Calculations of the characteristic ratios (C infinity) and persistence lengths (L-p) of novel liquid crystalline polyesters (LCPEs) containing the dihydroxy-alpha-methylstilbene (DH alpha MS) fragment were performed. The RIS Metropolis Monte Carlo (RMMC) method was used. RMMC enables the direct estimation of several: key conformational properties of polymer chains from atomistic simulations. Calculations were also performed for a single-chain analogue of VECTRA(TM) A900 (a commercial LCPE). The results, including the similar calculated exponential decrease of C infinity and L-p, with increasing absolute temperature, were very similar. The DH alpha MS isophthalate repeat unit, which is present at 10% by mole in the DH alpha MS-based LCPE, introduces 'kinks' and reduces the calculated C infinity and L-p, to the same level as for VECTRA(TM) A900. If it is replaced by DHaMS terephthalate, C infinity and L-p increase to almost 20% greater than those of VECTRA(TM) A900 which does not contain any moieties with a propensity to introduce kinks. Finally, DH alpha MS polycarbonate was calculated to be much stiffer than an ordinary random coil polymer, but much more flexible than any of the LCPEs which were modelled. (C) 1998 Elsevier Science Ltd. All rights reserved.