Prediction of liquid crystalline properties of poly(1,4-phenylene sebacate-oxybenzoate) by Monte Carlo simulation

Abstract

A Monte Carlo simulation study was undertaken to predict the liquid crystalline potential of a group of poly(1,4-phenylene sebacate-oxybenzoate) polymers. Molecular modelling procedures have been used to determine statistical parameters of isolated chains, with the objective of achieving a description which defines the tendency of a polymer molecule to form a liquid-crystalline phase, its mesogenicity. Initial attention was focused on the persistence length parameter as the most promising in this context to provide a description of mesogenicity which is equally applicable to molecules that consist of rigid segments separated by flexible sequences. A range of known mesogenic molecules has been modelled using RIS Metropolis Monte Carlo (RMMC) method based on carefully determined bond-rotation potentials which enabled the direct estimation of several key structural properties of the polymer chains. Evidence is presented to suggest that for liquid-crystalline polymer (LCP) molecules the nematic to isotropic transition occurs when the ratio of the persistence length to diameter (the persistence ratio) reaches a value of 5. The predictive possibilities of this criterion are explored in the estimation of the nematic–isotropic transition temperatures of the simulated polymers. RMMC was also applied to a well known LCP (poly( p-phenylene terephthalate)) in order to confirm the validity of the simulations. The results provide detailed quantitative information concerning the structural, orientational and liquid crystalline properties of the investigated copolymers as well as qualitative insights into the factors affecting the chain conformation.