Molecular dynamics simulation of azobenzene liquid crystalline polymers

This paper presents a computational conformational study undertaken to explain the liquid crystalline behaviour of some polyethers with high transition temperature values. The study is based on a very significant number of polymers and copolymers (over 1400) that were simulated to investigate the correlation between the chain geometry, flexibility, inter-chain interactions and orientational properties over liquid crystalline behaviour. Some of the simulated polymers were synthesised from 3,3-bis(chloromethyl)oxetane and various bisphenols with linear or bent geometry, such as 4,4'-dihydroxyazobenzene, 4,4'-dihydroxydiphenyl, bisphenol-A, 4,4'-dihydroxybenzophenone and 4,4'-dihydroxydiphenylsulfone. These polymers are of great interest as they allow chemical modifications due to the reactivity of the oxetane ring. For certain structures the molecular simulation evidenced difficult conformational changes associated with the distribution of the structural units in the chain. The phase transfer catalysis technique used for the polymer synthesis can generate different transfer ratios (from aqueous to the organic phase) for each bisphenol, with direct implications to the chain conformation. Therefore, the reaction conditions of the phase transfer catalyst can strongly influence chain conformation and the physical properties.