Quantum chemistry-based force field for simulations of poly(propylene oxide) and its oligomers

We present an atomistic force field for simulations of poly(propylene oxide) (PPO) and its low molecular weight oligomers. The force field is parametrized to accurately reproduce the relative conformer energies and rotational energy barriers in 1,2-dimethoxypropane (DMP) and 3,6-dimethyl diglyme (DMD) as determined from high-level ab initio electronic structure calculations. Partial atomic charges have been determined to accurately reproduce the electrostatic potential and dipole moments of important conformers of DMP and DMD as determined from quantum chemistry while yielding a charge neutral repeat unit for use in PPO simulations. The ability of the force field to accurately reproduce conformational energies is examined by comparing gas-phase molecular dynamics simulations of DMP with gas-phase NMR vicinal coupling measurements. The populations for the O-C*-C-O bond from simulations are found to be in good agreement with values determined from the experiments. The accuracy of the nonbonded interactions is examined through comparison of PVT data for liquid DMP from molecular dynamics simulations with experiment and predictions of DMP-water interactions using a quantum chemistry based force field for ether-water interactions with high-level ab initio calculations. In both cases good agreement is found.