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

摘要

Calculations of the characteristic ratios (C∞) and persistence lengths (L_p) of novel liquid crystalline polyesters (LCPEs) containing the dihydroxy-α-methylstilbene (DHαMS) 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 A900 (a commercial LCPE). The results, including the similar calculated exponential decrease of C∞ and L_p with increasing absolute temperature, were very similar. The DHαMS isophthalate repeat unit, which is present at 10% by mole in the DHαMS-based LCPE, introduces 'kinks' and reduces the calculated C∞ and L_p to the same levels as for VECTRA A900. If it is replaced by DHαMS terephthalate, C∞ and L_p increase to almost 20% greater than those of VECTRA A900 which does not contain any moieties with a propensity to introduce kinks. Finally, DHαMS 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.