A molecular dynamics simulation was done to analyze the glass transition temperature and the elasticity of polybutadiene using a single polymer chain. The radius of gyration of a free polymer chain without constraint was calculated at various temperatures to decide the glass transition temperature. When the end-to-end distance of a single polymer chain is constrained, a shrinkage force exerts on both ends. This constrained force was calculated for various end-to-end distances at 300K, by using POLYGRAF. The constrained force was estimated in two different ways for an average during 200ps calculations for each distance. One estimate came by calculating directly the force exerted between the end atoms, and the other came by estimating from the free energy expression of the system. The constrained force was compared with that of the Gaussian chain model. For the free polymer chain, a bend was found in the line relating radius of gyration and temperature, and its temperature was almost the same the an experimental glass transition temperature. The simulated force was in agreement with that of the Gaussian chain model before reaching a straight conformation, however, it increased rapidly when the polymer chain was further extended to a large end-to-end distance. An energetic force due to the van der Waals interaction among non-bonding atoms affected the elasticity of the polymer chain when it was in the random-coiling conformation at a small end-to-end distance.

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A new system utilizing an Imaging Plate (IP) was used to take X-ray fiber diagrams instead of the conventional photographic method. The IP has a large effective area, wide dynamic range, and high sensitivity. Presented here is an interactive computer program system for processing fiber diffraction data obtained by the IP. The system runs on the graphics workstation and it consists of three programs. The first program is to obtain the center of the diffraction pattern, the second one is to determine cell constants, and the third one is for intensity measurement. It was assumed that the shape of reflections is an ellipse and the background intensity along the radial and azimuthal directions changes linearly. The integrated intensity was measured by accumulating an intensity at each pixel within the ellipse after subtracting the background intensity. This system was applied to the structural analysis of a poly [ (4, 4′-diphenylene) pyromellitimide] fiber. The agreement factors with and without unobserved reflectons were R=0.202 and 0.143, respectively. This showed the high quality of the intensity data obtained by the new system presented here.

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In order to elucidate the stick-like spectra, e. g., C-13 high-resolution NMR spectra of polymers, two kinds of knowledge bases (KB) were designed on the basis of spectral information. One KB is for each stick-like spectrum and the other is for the spectrum of each polymer as a whole. Based on these KB, an expert system, PCMRES, was set up on a personal computer to compare the KB data with the input data for unknown compounds. After the first inference about the KB for individual peaks, the second inference about the latter KB, together with some empirical rules, is performed, and the preferable candidates are displayed. The KB includes about 1000 peaks of 100 samples. The final results are checked by comparing the stick-like spectra on the display. The basic concept of KB design can be applied to interpret other kinds of stick-like spectra.

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Diffusion of small molecules (penetrants) in polymers was studied by molecular dynamics simulation; special attention was paid on the anomaly of the diffusion found by Muller-Plathe et al. [Chem. Phys. Lett., 199, 237 (1992) ] . A simple model mimicking amorphous polyethylene, which contains oxygen molecules as a penetrant, was used. Also studied for comparison was Ar liquid as a representative of simple liquids. It was certainly confirmed that the penetrant diffusion approaches the hydrodynamic limit after 0.1ns, even when its self-diffusion coefficient is comparable to that of Ar liquid, i. e., -10-5cmcm2/s. Detailed analysis on hopping motions of the penetrant showed that the residence time distribution for the penetrant is fairly broad, possibly due to slower relaxation of the surrounding polymer segments. This feature, which was not observed for Ar liquid, was considered to cause the anomaly in the time scale comparable to the mean residence time. Based on this observation, the time scale necessary for evaluating the penetrant diffusion was discussed.

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Reactions for the formation of the phenolic co-condensation resins such as the p-cresol/p-tert-butylphenol/formaldehyde system and o, o-dimethylol-p-cresol/o, o-dimethylol-p-tert-butylphenol system were investigated by computer simulation, and the monomer reactivity ratios and the compositions of the resins were discussed. The computer simulation was carried out under the following assumptions: 1) intramolecular reaction does not occur, 2) the reaction forming a dimethylene ether linkage (-CH₂OCH₂-) does not occur in the p-cresol/p-tert-butylphenol/formaldehyde system, and 3) the reactivity of a functional group in polymer is independent of the size and molecular weight. In this simulation, the reactivity of each functional group was represented by the probability that the group stored in the computer was selected. It was found that the reactivity of p-cresol was higher than that of p-tert-butylphenol in the addition-condensation reaction. While, the reactivity of o, o-dimethylol-p-cresol was almost equal to that of o, odimethylol-p-tert-butylphenol in the polycondensation reaction. The compositions of these resins were estimated from the values of monomer reactivity ratios obtained by the computer simulation. The resin formed by the additioncondensation reaction contained more of the p-cresol component than ideal copolymer systems (r1=r2=1). Contrary, the resin formed by the polycondensation contained slightly more of the o, o-dimethylol-p-tert-butylphenol component. This may be due to the effect of the p-substituent in the phenolic nucleus on the addition reaction of formaldehyde with a phenolic hydrogen.

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Mlecular conformation of the repeating units of κ-carrageenan was investigated as the first step to clarify the solution conformation of carrageenan and the related polysaccharides by using the simulation methods of the molecular mechanics and molecular dynamics. The repeating units of κ-carrageenan consist of the 4, 1 linked and 1 3 linked dimers of the 3, 6-anhydroα-D-galactose andβ-D-galactose-4-sulphate. Potential energy maps for both 4, 1 and 1, linked dimers were obtained as a function of the dihedral angles for their glycosil linkages. The energy map for the 1, linked dimer was found to have large minimum area, where the dihedral angles of the glycosil linkage can fluctuate easily at room temperature. When the sulphate group was removed from the 1, 3 linked dimer, the above area was limited to around the (0=171, 0=188). This area corresponds to the one for the double helical conformation of carrageenan obtained from X-ray diffraction experiment. From the analysis of the molecular dynamics simulation of the dimer units with surrounding water molecules, a bridge of the hydrogen bonds which include a water molecule between pyranose rings of the 1, 3 linked dimer was found. This may play an important role in the stability of a conformation in water.

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A new method for protein structure determination in solution has been proposed by a combination of distance geometry calculation (DADAS90) and ¹H NMR chemical shift calculation for proteins. When the ring current shielding effect from the aromatic ring in protein on an α-CH proton is larger than 0.3ppm, the distance constraints from the aromatic rings to the α-CH protons are incorporated into the process of DADAS calculation using the co-ordinates from the X-ray diffraction analysis. A better structure for BPTI (Basic Pancreatic Trypsin Inhibitor) with a good correlation between calculated and observed α-CH chemical shifts, and with a small value of the target function, is obtained by taking into accountsuch a ring-current shielding effect.

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In order to analyzed ¹⁷O NMR powder patterns of polymers in the solid-state with separation of nuclear quadrupolar interaction and chemical shift interaction, we developed a computer analysis method for solid state ¹⁷O NMR spectra on the basis of quantum mechanics. Using this method, we successfully carried out spectral analysis of the solid state ¹⁷O NMR powder patterns for polyglycine.

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Sequence distributions of copolymers obtained by nonequilibrium polycondensation of a diacid dichloride with two kinds of diols were investigated by means of computer simulation. The simulated data were compared with the experimental results given by Korshak et al. Large difference in reactivity between two (or more) diols did not affect the unit sequence distribution of the copolymer when prepared by monophase solution polycondensation. The sequence distribution of one diol in the copolymer was equal to the theoretical molecular weight distribution of oligomers which was produced on the assumption that the consumption ratio of the diacid dichloride to the diol was their feed ratio. In two step polymerization, stepwise addition of the diacid dichloride increased the blockness of the copolymer. In the non-monophase polymerization, the dissolving rate of the solid diacid dichloride increased the blockness of the copolymer. With an increase in the difference in the reactivity between the monomeric diacid dichloride and an acid chloride residue existing at the end of oligomers, alternativeness of the copolymer increased.

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Sequence distribution of poly [ (1, 4-phenyleneterephthalamide) -co- (1, 3-phenyleneoxy-1, 4-phenyleneterephthalamide) ] (Technora R) prepared by nonequilibrium copolycondensation, where solid terephthalic acid dichloride (TPC) was added to a solution of p-phenylenediamine (PPDA) and 3, 4′-diaminodiphenylether (3, 4′-DAPE), was inestigated by means of computer simnulation of the polymerization. The molecular weight distribution of oligomers, which were obtained under the conditions similar to the process of TechnoraR synthesis but with deviating monomer feed ratio from unity, was different from the theoretical value calculated by Flory's well-known equation. Thus the simulation model of the polymerization was modified so that the calculated molecular weight distribution would coincide with the experimental value. The simulation clarified that the conditions of dissolution and diffusion of TPC added as solid brought a change in the molecular weight distribution. The dissolution and diffusion parameters used in the simulation were estimated so as to coincide with the experimental values of the molecular weight distribution. The sequence distribution of TechnoraR given by the polymerization simulation, which was modified with the estimated parameters, was virtually equal to that of a statistical random copolymer due to a small difference in reactivity of the two diamines.

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