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The bulk phase of poly(p-xylylene) (PPX) at 295−595 K and isolated PPX chains at 195−995 K have been simulated by molecular dynamics using TraPPE-UA model potentials. Thermodynamic properties, molecular mobility, and structural characteristics have been studied. Transitions observed when heating the model systems have been examined. It has been found that the simple model potential allows us to reproduce satisfactorily a number of experimental characteristics of PPX at relatively high temperatures when experiment shows formation of conformationally disordered phases.

Association equilibrium has been studied by molecular dynamics (MD) for mixtures of cross-associating molecules (n-decamer+p-dimer and n-decamer+p-decamer) in a good solvent. Each monomer of n-decamers carries an associative site (n-sticker); each molecule of the second component contains two terminal associative sites (p-stickers). To model the univalent association between the n-sticker and the p-sticker, a technique based on introduction of dummy atoms has been used. We report MD data on the effects of temperature, chain flexibility, and location of the sticker within the chain on the association equilibrium. We find that the presence of nonassociating monomer units of p-chain has a substantial effect on the association equilibrium. This effect is similar to "crowding" in reactive mixtures known to be caused by the presence of inert molecules. Widely used mean field theories of associating chains (e.g., SAFT or Semenov-Rubinstein theory) do not account for the effect of crowding caused by the inert fragments of reactive chains. We introduce simple empirical corrections for crowding that describe association equilibrium in the presence of nonassociating fragment in a chain-like molecule.

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Thermodynamic properties (configurational energies, compositions, densities) and structural characteristics of coexisting liquid and vapor phases in the ethanol−ethane binary system at the temperature 348.15 K in the pressure range 1.70−7.83 MPa are calculated by the Gibbs ensemble Monte Carlo method. Obtained values are in satisfactory agreement both with the experimental data and the results of the application of the hole quasichemical group-contribution model (at pressures far enough from the critical point). The calculated phase diagram at 348.15 K agrees satisfactorily with the experimental one; the value of the critical pressure obtained from simulations is about 13% lower than that from the experiment.

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