Shigeru Yao

Ti atom in MFI zeolite framework: a large cluster model study by ONIOM method

Abstract Ti atom siting in MFI zeolite framework was studied using one large cluster model containing about 200 atoms, which was made by trimming of MFI zeolite crystal, by means of ONIOM quantum mechanics/molecular mechanics (QM/MM and QM/QM hybrid) method. Si atoms at 12 T sites were replaced succeedingly with a Ti atom and resulted Ti(OSi)4 moiety was locally relaxed by ONIOM (B3LYP/Lanl2dz:UFF) method. The other atoms at crystallographic structure of MFI zeolite framework were treated as an inorganic matrix and fixed at its original position. Single-point energies of T sites were calculated for the optimized structure by ONIOM (B3LYP/Lanl2dz:B3LYP/Lanl2mb) and the relative stability between T sites was compared.

Consideration of an activity of the metallocene catalyst by using molecular mechanics, molecular dynamics and QSAR

Abstract Recently metallocene based catalyst are widely used for the olefin polymerization catalyst. It is well known however that the metallocene catalysts do not show any activity without cocatalyst and also their activity depends on content and species of cocatalyst. In this study, the most stable structures of various catalyst–cocatalyst systems were calculated by using molecular mechanics (MM) and molecular dynamics (MD). Various structural parameters which are related to the space between central atoms of catalyst and cocatalyst, charges, and interaction energy were obtained from those structures. By using the quantitative activity–structure relationship (QSAR) analysis, the space between catalyst and cocatalyst was found to be the main factor to control the activity. By using this acknowledgment the activity of the metallocene catalyst may be roughly estimated without using the heavy ab initio molecular orbital calculation.

Theoretical Consideration of the External Donor of Heterogeneous Ziegler–Natta Catalysts Using Molecular Mechanics, Molecular Dynamics, and QSAR Analysis

In the previous paper we calculated the most stable structure of the catalyst and cocatalyst of metallocene catalyst systems using molecular dynamics and molecular mechanics. In this paper we postulate the active site of the heterogeneous Ziegler–Natta catalyst, and analyze it by the same methods to clarify the main factors that control the activity and molecular weight distribution of the heterogeneous catalyst systems. The roles of the external donor were also considered, and we found that the interaction energy between an external donor and the active site of the catalyst, as well as the structural factors of the external donor itself, are strongly related to both activity and molecular weight distribution. These results reveal that molecular dynamics and molecular mechanics calculations are also effective methods to screen the heterogeneous catalyst systems.

Polymerization and copolymerization of N-cyclododecylmaleimide

Abstract Homopolymerizations and copolymerizations of N-cyclododecylmaleimide (CDMI) were performed at 60°C in the presence of azobisisobutyronitrile (AIBN) as an initiator in tetrahydrofuran. The initial rate of polymerization was Rp = k[AIBN]0.50[CDMI]3.4, where k is the rate constant. Overall activation energy (E) and frequency factor (A) were 19.2 kcal mol−1 and 2.0 × 109 s−1, respectively. The monomer reactivity ratios in the copolymerization of CDMI (M1) with styrene (ST; M2) or methyl methacrylate (MMA; M2) and Alfrey-Price Q, e values were determined as: r1 = 0.10, r2 = 0.102, Q1 = 1.77, e1 = 1.34 in CDMI-ST system; r1 = 0.19, r2 = 1.31, Q1 = 0.91, e1 = 1.58 in CDMI-MMA system. The thermostabilities of the polymers and copolymers were investigated by differential scanning calorimetry and thermogravimetric analysis.

Rheological Properties of Disperse Systems of Photosensitive Particles: II. The Influence of Particle Aggregation on Slow Relaxation Process

Rheological properties of disperse systems of photosensitive particles were studied in relation to the degree of aggregation of dispersing particles. Photosensitive particles were prepared by introducing cinnamoyl groups to styrenedivinylbenzene copolymer spherical particles. The degree of aggregation (total number of primary particles forming an aggregate) was controlled by irradiation of light to the disperse system and was estimated from light scattering by assuming a hexagonal close‐packed aggregate model. Viscoelastic properties of the disperse systems of the photosensitive particles in diethylphthalate were measured by means of a cone‐plate type rheometer. Terminal zone of the modulus shifts progressively to lower frequency with increasing the irradiation time, i.e., with increasing the degree of aggregation. It is strongly suggested that the aggregate is a cause of the long‐time relaxation and that the maximum relaxation time of the disperse system can be directly related to the rotational diffusio...

The chemical structure dependence of interaction strength between polymers and mobility of polymer chains in the polymer interface

Abstract The structural difference of the interface between polypropylene pair (PP/PP) and polypropylene and poly(ethylene-alt-propylene) pair (PP/EAP) was investigated using molecular dynamics and molecular mechanics, under a two-dimensional periodic boundary condition (2DPBC). From the position of the end group of each polymer chain, the influence of the chemical structure and the mobility of the polymer chain were considered. In the PP/PP system, the end group is mainly located in the middle region of each polymer layer. In the PP/EAP system, the PP end group and the ethylene end group of EAP are also located in the middle region of each polymer layer, but the propylene end group of EAP is located very near the interface. These results suggest that the mobility of the middle part of the polymer chain is not so small, and that the similarity in the chemical structure, which is a measure of the interaction strength between polymers, plays an important role in the early stage of adhesion. An easy and efficient estimation method of the interaction strength between polymer pairs is also proposed, and the influence of the component sequence in copolymer on the interaction strength is systematically estimated.

Influence of bound water on viscoelastic enhancement in aqueous disperse systems of ionic microgels

The viscoelastic properties have been measured by means of a cone–plate-type rheometer for aqueous disperse systems of ionic microgels. Marked viscoelastic enhancement was observed in some aggregate systems in which anionic and cationic particles were mixed. The dynamic viscoelastic functions of these aggregate systems were enhanced ca. 105 times with respect to those of non-aggregate systems, suggesting that the aggregate contains a large quantity of bound water which is tightly arranged in the electrostatic potential field between oppositely charged particles. The bound water was investigated by d.s.c., dielectric measurements and n.m.r. spectroscopy. Two kinds of bound water were detected by d.s.c. and dielectric measurements. The dielectric relaxation time of the bound water which seems to take part in the viscoelastic enhancement was ca. 8.9 × 10–9 s.

Novel Time‐Dependent Rheological Phenomenon in Suspensions of Spherical Particles

A novel time‐dependent phenomenon has been found in the rheology of the disperse system of spherical particles. This is the phenomenon that the dynamic torque, i.e. the dynamic moduli, decrease with increasing dynamic shearing time to values lower than one‐thousandth of their initial ones and recover within a short time by the appropriate steady shear. This unsteady phenomenon can be repeated many times by repeating the shearing process. It is considered that the rigidity and the uniformity in shape and size of dispersing particles are important factors for this time‐dependent phenomenon.

Thermal process-dependence of the mechanical properties and inner structures of pre-consumer recycled polypropylene

Recycled plastics are considered to have less-desirable mechanical properties and durability than virgin materials, and this is usually thought to be due to chemical degradation. However, we recently found that pre-consumer polypropylene (Pre-RPP) was not chemically degraded and had almost the same molecular properties as virgin polypropylene (VPP). In this study, we subjected recycled pre-consumer polypropylene to various thermal treatments and found that we could obtain properties similar to those of virgin polypropylene. We also investigated the fracture surfaces by SEM. The results showed that the mechanical properties were closely related to the inner structure, and if we can control the inner structure of Pre-RPP we may be able to improve its mechanical properties and durability so that they are almost the same as those of VPP.

Dynamic Measurements on Polymer Liquid Crystals

Abstract The dynamic experiments were made on the solutions of poly (l,4-phenylene-2,6-benzobisthioazole) (PBT) in poly(phosphoric acid) at frequencies from 10−2 to 102 radian· sec−1. For the liquid-crystalline solutions, the logarithmic plots of G′ and G″ against frequency show abnormally small slopes and those of η′ exhibit large slopes at low frequencies in contrast to the plots for the optically isotropic solutions. However, the viscoelastic behavior of liquid-crystalline solutions is regarded as linear. The temperature of anisotropic-isotropic phase transition of solution is higher for high-molecular-weight PBT than for lowmolecular-weight PBT. The dilution of solution lowers the transition temperature. The transition goes through various stages of mixed phases. The method of reduced variables is applicable to the isotropic solutions, and the resulted composite curves were discussed. The method, however, is inapplicable to the anisotropic solutions, suggesting that the configuration, interaction and aggregation state of molecules in liquid-crystalline solutions may change sensitively by temperature. The slow relaxation mechanisms are involved in the mesophase systems, but the quick shrinkage of highly oriented nematic mesophase at the onset of relaxation produces the zigzag-fibrillar structure of fibers and films made by stretch spinning or casting.