Conformations of 2,4-Diphenylpentane: A Quantum Chemistry and Gas-Phase Molecular Dynamics Simulation Study

Rearrangement of Nanoporous Cavity Structures in Crystalline Syndiotactic Polystyrene Associated with Stress-Induced Phase Transition

This work demonstrates the possibility of rearranging nanoporous cavity structures in crystalline syndiotactic polystyrene (s-PS) by applying external stresses. A molecular dynamics (MD) simulation was performed for the s-PS crystal with increasing or decreasing of each stress tensor component, starting from the nanoporous ε form. Upon uniaxial compression along the b-axis, the ε form was transformed into a lower density porous form, accompanied by significant elongation of the a-axis. The new form, named the S-I form, was stable only under the stress and was transformed into the γ form after release of the stress. The cavity structure was drastically changed by the transition. The straight cylindrical channels in the ε form, which may be used for the separation of organic solvents, were rearranged to narrower zigzag channels in the S-I form, which is suitable for the precise separation of gases. The molecular cavities disappeared after release of the stress, associated with the transition to the γ form.

Effect of encaged aromatic guests on the shape and connectivity of molecular cavity in crystalline polystyrene evaluated by molecular simulations

The delta form of crystalline syndiotactic polystyrene is a clathrate molecular compound in which various aromatic molecules are encaged. We have investigated the size, shape, and connectivity of the molecular cavity in the crystal using a molecular dynamics simulation. The effects of the guest species on the cavity structure were investigated in detail. In order to systematically vary the guest structure, various aromatic guests, e.g., benzene, toluene, p-xylene, m-xylene, o and mesitylene were examined. The interstitial spaces between the guests and the polymer chains were analyzed by cluster analysis of the free volumes. The individual cavity volumes into which the guests are clathrated were also evaluated. It was found that the guest molecules can greatly affect not only the cavity size and shape but also the connectivity of the cavities. The transport of small molecules in the crystal is discussed in connection with the cavity structure.