A molecular dynamics simulation of bulk atactic polystyrene was performed. A united atom model and an all atom model were developed, in both of which the bond lengths were held fixed and the phenyl group was represented by a rigid, planar hexagon. The degree of success of the simulation was examined by comparing the calculated X-ray scattering intensity curve with experiment. The united atom model reproduces the so-called "polymerization peak", and the calculated curve agrees well with one of the most recently published experimental data. The degree of agreement achieved is in fact comparable to the degree to which two published experimental curves agree with each other. The agreement in the radial distribution function between the calculated and experimentally derived one is good in the r range smaller than 9 Á but deteriorates somewhat for larger r. There are again uncertainties in the experimental radial distribution function itself at large distances, however, as can be seen by comparing experimental curves obtained by two different groups. In contrast to the united atom model, the all atom model was found to give a result which clearly disagrees with experimental results, and one of the commercially available software gave an even worse result. The nature of smearing that accrues in the experimentally determined radial distribution function, as a consequence of the differing q dependencies of C and H atomic scattering factors and the limited q range accessible to experiment, has been examined by calculating the radial distribution function directly from the simulation result.

Poly(β-phenylpropyl l-aspartate) exhibits a novel helix−helix transition in the solid state at around 160 °C. The transition takes place reversibly in a narrow temperature range during a heating and cooling cycle, indicating that it is essentially of a first order. A combined use of circular dichroism, X-ray, and 13C CP/MAS NMR measurements revealed that the transition is due to an interconversion of the helical screw sense from a right-handed α-helix to a left-handed helix. An unwinding and rewinding of the helical screw occurs concertedly along the polypeptide backbone without disturbing the uniaxial orientation of the helix axes.

Phase behavior and ordering characteristics were reported for poly(γ-benzyl l-glutamate) (PBLG) in a mixed solvent containing a denaturant acid, dichloroacetic acid (DCA), + dichloroethane (DCE). The solutions of PBLG prepared so as to be liquid crystal at room temperature were observed to undergo a reentrant isotropic transition at low temperature where conformational disordering of PBLG molecules takes place. The deuterium quadrupolar splitting data obtained by the 2H NMR method were analyzed to elucidate the conformation and orientational order parameter of the α-helix in the liquid crystalline phase. The conformation of PBLG molecules in the isotropic state was estimated from the observed 13C NMR chemical shift. The molecular information gained through these experiments was implemented into the theoretical expression set forth by Flory and Matheson. The phase diagrams calculated on this basis have been compared with those observed. The theory has provided a reasonable picture for the high- and low-temperature phase transitions of the PBLG/DCA/DCE system.

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The binding properties of trivalent ions to polyacrylate and its low molecular weight analogs (monomer, dimer, and trimer) were investigated in dilute aqueous solution (10-2−10-3 M) using Tb3+ ion as a fluorescent probe. The fluorescence intensity and lifetime of the Tb3+ ion depend directly on the number of water molecules bound to their inner coordination sphere. The more efficiently ligands coordinate to Tb3+ ion, the more water molecules are expelled and, consequently, the greater the fluorescence intensity and lifetime observed. Lifetime measurements in H2O and D2O showed that the number of water molecules coordinated to the Tb3+ ion are 6.5, 6.1, 4.9, and 3.6 for monomer, dimer, trimer model compounds, and polyacrylate, respectively. The viscosities of Tb3+−polyacrylate complexes were measured in the presence of a large excess of sodium bromide. Viscosities (ηsp/c) of the polyacrylate solutions follow Huggins' equation, and on addition of Tb3+ ion, the intrinsic viscosities decrease abruptly from 700 to 40 mL/g. The mean end-to-end distances, 〈r 2〉1/2, for polyacrylate in Tb3+−polymer complexes were calculated using the Flory−Fox equation and were found to be reduced from 125 to 48 nm on addition of Tb3+. These results indicate that of the nine water molecules coordinated to Tb3+ ion in aqueous solution, five to six are replaced with carboxylate groups attached to the polymer chain wrapped around the Tb3+.