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Using a large polymer chain cluster, we have examined entanglement densities of the polymer chains in the bulk and in the surface by molecular dynamics simulation. The entanglement density was measured by the interchain contact fraction (ICF), which was developed as a structural parameter of the entanglement. It was found that the surface location has a lower ICF than the bulk core does. Different entanglement structures then underwent crystallization processes. It resulted in a multidomain system, in which the directors of the order domains are in isotropic distributed. For calculating the crystallinity of the systems, we developed a method, the site order parameter (SOP), which endows local order to every particle in the system; when determining the order for crystalline phase, one can count the crystallinity. SOP enables us to transform a molecular chain picture into an order image, where white stands for the crystalline phase and black for the amorphous. Snapshots of the simulations show evolution of the nucleation and the crystal growth through SOP images. The dynamic effect of the entanglement was observed in the crystallization behaviors. It shows that the entanglement has a higher density in the bulk and a lower density in the surface. The result shows that a shorter induction period of nucleation and a higher crystal growth rate was found in the surface location, since possessing lower ICF.

A vibrational analysis has been carried out to analyze the chain conformation of poly(lactic acid) in the crystalline state. In conjunction with a normal-coordinate analysis, the Raman spectrum has yielded data regarding conformational distributions. Raman spectra of different helices were simulated using previously published structures, force constants, and intensity parameters. Some of the chain conformations predicted are inconsistent with the data. Only one of the four 31 helical structures predicted by conformational analysis agrees well with experiment. This analysis provides a new understanding regarding the relative probability of a 103 or 31 helix for poly(lactic acid).

Isotropic Raman spectra of poly(ethylene oxide) in aqueous solution and in the melt show differences in the skeletal stretching vibration bands near 800 cm-1 and in the disordered longitudinal acoustic mode feature in the 200−400 cm-1 region. These spectra may be simulated by superposing calculated spectra resulting from a series of normal coordinate calculations performed for an ensemble of conformers. The conformational distribution for poly(ethylene oxide) in the molten state appears to favor the tgg‘ conformer, which dominates the spectrum calculated to match closely the observed isotropic Raman spectrum. It appears that the experimental data suggest that the tgg‘ conformation is present by a greater amount than is predicted by previous simulation methods. On the same basis, it appears that the aqueous solution of poly(ethylene oxide) contains mostly tgt conformers. The results for poly(ethylene oxide) were supported by measurements and computations made using 1,2-dimethoxyethane as a model.

Phase separation behavior associated with ultrathin films of model polyurethanes has been studied by reflectance infrared spectroscopy. Our data clearly demonstrate that the phase separation behavior and the domain size of polyurethanes in the ultrathin film region differ significantly from its bulk state. The kinetics measured are considerably slower than the bulk state. In addition, the degree of phase separation is also highly dependent on film thickness. The phase separation obeys an Aurami type rate process. Using a Monte Carlo simulation method to fix the location and orientation of the nucleating points, the phase separation behavior can be modeled

One of the novel multidimensional charge-transfer (CT) chromophores, 2-[4-(4,5-di(4-nitrophenyl)imidazolyl)phenyl]-4,5-di(4-aminophenyl)imidazole (DNPIPDAPI), was designed and synthesized; the polyimide was formed with it and 2,5-bis(4-aminophenyl)-3,4-diphenylthiophene (TPTDA) (BMI) The thermal and temporal stability of the poling-induced orientation were evaluated. The temporal orientation of the poled polyimide film with DNPIPDAPI was over 1000 h at 150 °C, retaining 85% of the initial d 33 value. Comparing with 1-D chromophores, the synthetic multiple CT chromophore possesses a better property in controlling the decay of the SHG activity.

The orientation and phase separation in ultrathin films (40-300 A) of model polyurethanes with monodisperse hard segments were studied as a function of film thickness and of the substrate on which the polymer is cast. It is found that the thin films are more phase mixed and the hard segments in both domains are more oriented in the plane of the surface than are the bulk polyurethane films. Upon annealing, the excess phase mixing and orientation of the phase domains decreases the mobility of on the surface and prevents further changes.

The molecular simulation technique was successsfully used to calculate structures of polyethylene, poly(p-phenylene terephtalamide) (PPTA) and poly(p-benzamide) (PBA). The calculated unit cell parameters compared favorably with experimental data. The simulated deformation behavior of PPTA is consistent with the expectations because strong specific hydrogen-bonded interactions dominate the stability of the three dimensional structure. The deformation mechanism of PBA in the single chain approximation was found to differ considerably from that in the full three dimensional model.

Mesure par irradiation IR non polarisee de l'orientation moleculaire de l'hexahydroxybenzene hexa(n-octanoate-6,6d 2 et d'un poly(benzene hexa-n-alcanoate)