COMPUTER-SIMULATIONS OF POLY(ETHYLENE OXIDE) - FORCE-FIELD, PVT DIAGRAM AND CYCLIZATION BEHAVIOR

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 atomi stic simulations to study PVT (pressure, volume, temperature) and cohe sive properties of oligomeric poly(ethylene oxide) (PEG) and related s mall-molecule liquids, and the second to study the extent of ring form ation in polymerization of poly(ethylene glycols) (PEGs) and hexamethy lene diisocyanate (HDI). The atomistic simulations, focusing extensive ly on liquids and amorphous poly(ethylene oxides), demonstrate the abi lity to predict densities with an accuracy of 1%-2% over extended rang es of at least 200K in temperature and 180 MPa in pressure. Densities of related small-molecule liquids, dimethyl and diethyl ether and etha nol at or close to saturation pressure are also well. reproduced to te mperatures 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 ma terial. Additionally, crystal structures can also be well predicted. F or the polymerization studies the Monte Carlo network simulation metho d was modified to mimic diffusion of reactants during the polymerizati on. Application to the PEG/HDI 'linear' polymerization system, using c hain 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 co nditions ranging from the bulk to highly dilute reaction conditions.