Computer simulations of poly(ethylene oxide): force field, pvt diagram and cyclization behaviour

Parametrization of a force field capable of quantitatively describing the gas, liquid and crystal phases of alcohols, ethers and polyethers is described. Two applications are reported, the first employing atomistic simulations to study PVT (pressure, volume, temperature) and cohesive properties of oligomeric poly(ethylene oxide) (PEO) and related small-molecule liquids, and the second to study the extent of ring formation in polymerization of poly(ethylene glycols) (PEGs) and hexamethylene diisocyanate (HDI). The atomistic simulations, focusing extensively on liquids and amorphous poly(ethylene oxides), demonstrate the ability to predict densities with an accuracy of 1%–2% over extended ranges of at least 200K in temperature and 180MPa in pressure. Densities of related small-molecule liquids, dimethyl and diethyl ether and ethanol at or close to saturation pressure are also well reproduced to temperatures close to the critical temperature. Densities calculated for methoxy-terminated oligomers are used to predict the density of melt and amorphous high-molar-mass PEO with an accuracy of better than 1%. Similarly, solubility parameters have been calculated as a function of chain length for poly(ethylene glycol) oligomers and used effectively to obtain estimates of the solubility parameter of high-molar-mass material. Additionally, crystal structures can also be well predicted. For the polymerization studies the Monte Carlo network simulation method was modified to mimic diffusion of reactants during the polymerization. Application to the PEG/HDI ‘linear’ polymerization system, using chain configurations generated with the atomistic force field, reveals a major improvement in the ability of the method to predict the extent of ring formation without adjustable parameters for polymerization conditions ranging from the bulk to highly dilute reaction conditions. ©1997 SCI