Molecular Dynamics Simulation of Azobenzene Liquid Crystalline Polymers

Abstract

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 1 400) 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.

Molecular dynamics simulation of diffusion of O2 and CO2 in blends of amorphous poly(ethylene terephthalate) and related polyesters

“…The Dreiding 2.21 force field described by Mayo et al [37] and implemented in Cerius 2 OFF module was applied since it was found to be very suitable and reliable for the molecular simulation of aromatic polymers in accordance with previous studies [37][38][39][40][41][42]. This force field is parametized for a large class of organic molecules involving H, C, O, S, P, F, Cl and Br, allowing it to be applied to bio-and synthetic polymers [35][36][37][38][39][40][41][42]. It was found that the Dreiding 2.21 force field leads to accurate geometries for various polymeric systems and can be used to calculate and minimise the energy of a simulated polymeric system.…”

“…The non-canonical 'T-damping' thermostat described by Berendsen et al [46,47] was used for isothermal-isobaric NPT-MD simulations. Molecular dynamics studies [25][26][27][28][29][30][31][32][37][38][39][40][41][42][43] have proven to provide a better insight into the physical phenomena exhibited by polymers. In the case of polymers, this technique can actually be used to predict physical (density, diffusion, and free volume) properties of a polymeric system.…”

“…The Mie 6-12 potential [39][40][41][42][43][44], that is often referred to in the literature as the Lennard-Jones 6-12 potential function (uZA/r 12 KB/r 6 ), was used to calculate the non-bonded van der Waals interactions. A and B are parameters which determine the size of the attraction (KB/r 6 ) and repulsion (A/r 12 ) interactions between the atoms which are separated by a distance r equal to the sum of r i and r j , where r i and r j are van der Waals radii of the non-bonded atoms i and j.…”

Thermal and kinetic characteristics in non-isothermal conditions of some aromatic copolyethers containing an octomethylenic spacer

“…For a better understanding of this behavior, theoretical conformational analyses were e®ectuated. In our previous studies, the molecular modeling was very helpful in explaining the speci¯c degradation phenomena [8,12,13] or supra-molecular behavior [14,15,16,17]. If the polar surface is less than 5-5.5%, these studies indicate that the degradation process is not a®ected by the chain polarity [12,13].…”

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

“…In fact, an important goal in the synthesis of LCP is to design molecules with the necessary order to form a mesophase yet with sufficient chain flexibility so that the crystal melting temperature (T m ) is reached within the range of normal processing temperatures. Due to their unique physical properties like high strength and modulus, good thermal endurance, small linear expansion coefficient (comparable with ceramics), high chemical resistance, significant attention has been devoted to these materials [9][10][11][12][13][14][15]. One of the distinguishing structural properties of these polymers is the ease in producing a uniform molecular orientation [16][17].…”