Phenolic Polymer Solvation in Water and Ethylene Glycol, I: Molecular Dynamics Simulations.

Interactions between pre-cured phenolic polymer chains and a solvent have a significant impact on the structure and properties of the final postcured phenolic resin. Developing an understanding of the nature of these interactions is important and will aid in the selection of the proper solvent that will lead to the desired final product. Here, we investigate the role of the phenolic chain structure and the solvent type on the overall solvation performance of the system through molecular dynamics simulations. Two types of solvents are considered: ethylene glycol (EGL) and H2O. In addition, three phenolic chain structures are considered, including two novolac-type chains with either an ortho-ortho (OON) or an ortho-para (OPN) backbone network and a resole-type (RES) chain with an ortho-ortho network. Each system is characterized through a structural analysis of the solvation shell and the hydrogen-bonding environment as well as through a quantification of the solvation free energy along with partitioned interaction energies between specific molecular species. The combination of simulations and the analyses indicate that EGL provides a higher solvation free energy than H2O due to more energetically favorable hydrophilic interactions as well as favorable hydrophobic interactions between CH element groups. In addition, the phenolic chain structure significantly affects the solvation performance, with OON having limited intermolecular hydrogen-bond formations, while OPN and RES interact more favorably with the solvent molecules. The results suggest that a resole-type phenolic chain with an ortho-para network should have the best solvation performance in EGL, H2O, and other similar solvents.

Phenolic Polymer Solvation in Water and Ethylene Glycol, II: Ab Initio Computations.

Ab initio techniques are used to study the interaction of ethylene glycol and water with a phenolic polymer. The water bonds more strongly with the phenolic OH than with the ring. The phenolic OH groups can form hydrogen bonds between themselves. For more than one water molecule, there is a competition between water-water and water-phenolic interactions. Ethylene glycol shows the same effects as those of water, but the potential energy surface is further complicated by CH2-phenolic interactions, different conformers of ethylene glycol, and two OH groups on each molecule. Thus, the ethylene glycol-phenolic potential is more complicated than the water-phenolic potential. The results of the ab initio calculations are compared to those obtained using a force field. These calibration studies show that the water system is easier to describe than the ethylene glycol system. The calibration studies confirm the reliability of force fields used in our companion molecular dynamics study of a phenolic polymer in water and ethylene solutions.

Structure and energetics of Li(+)-(BF4(-))n, Li(+)-(FSI(-))n, and Li(+)-(TFSI(-))n: ab initio and polarizable force field approaches.

The Li(+)-BF4(-) and BF4(-)-BF4(-) interactions are studied using second order perturbation theory (MP2) and coupled cluster singles and doubles approach, including the effect of connected triples, CCSD(T). The MP2 and CCSD(T) results are in excellent agreement. Using only the MP2 approach, the interactions of Li(+) with bis(trifluoromethane)sulfonimide anion (TFSI) and Li(+) with bis(fluorosulfonyl)imide anion (FSI) are studied. The results of these high level calculations are compared with density functional theory (DFT) calculations for a variety of functionals and with the APPLE&P force field. The B3LYP approach well reproduces the accurate calculations using both a small and large basis set. The M06 and M06L functionals in the larger basis set are in good agreement with the high level calculations. While the APPLE&P force field does not outperform the best functionals, the APPLE&P results agree better with the accurate results than do some of the functionals tested.