Nonisothermal crystallization kinetics of poly(beta-hydroxybutyrate)

Kinetics of nonisothermal crystallization of poly( beta-hydroxybutyrate) from melt and glassy states were performed by differential scanning calorimetry under various heating and cooling rates. Several different analysis methods were used to describe the process of nonisothermal crystallization. The results showed that both Avrami treatment and a new method developed by combining the Avrami equation and Ozawa equation could describe this system very well. However, Ozawa analysis failed. By using an evaluation method, proposed by Kissinger, activation energies have been evaluated to be 92.6 kJ/mol and 64.6 kJ/mol for crystallization from the glassy and melt state, respectively. (C) 1998 John Wiley & Sons, Inc.

Spontaneous assembly of the inclusion complexes of viologen-attached alkanethiols and alpha-, beta-cyclodestrin on gold electrode

Electroactive self-assembled monolayers (SAMs) with well-defined electrochemical responses were prepared by spontaneous assembly of the inclusion complexes (CD/C8VComegaSH) of viologen-attached alkanethiols (C8VComegaSH) and alpha- and beta-cyclodextrin (CD). They were characterized by X-ray photoelectron spectroscopy and cyclic voltammetry. The results demonstrate that the chemisorption process of CD/C8VComegaSH on gold substrate occurs through S-Au bonds, and that the redox sites in SAMs of CD/C8VComegaSH are in a much more uniform environment than those in SAMs of C8VComegaSH.

Crystallization kinetics and morphology of poly(beta-hydroxybutyrate) and poly(vinyl acetate) blends

The crystallization behavior and morphology of poly(beta-hydroxybutyrate) and poly(vinyl acetate) blends have been studied with DSC, POM, SAXS and WAXD methods. The results indicate that the overall crystallization rate and spherulite growth rate are slower in the blends than that in the pure PHB. The addition of PVAc has no effect on the crystal structure of PHB, but affects its crystalline morphology. During crystallization of PHB, PVAc chains were being rejected into the region between the lamellae of crystalline PHB. (C) 1997 Elsevier Science Ltd.

Theoretical study on the unimolecular fragmentation of ionized tetrahydroimidazole-substituted methylene beta-diketones

Semiempirical molecular orbital calculations on the unimolecular mass spectrometric fragmentation of tetrahydroimidazole-substituted methylene beta-diketones are carried out by Austin Model 1 method, and the calculated results give a strong support to our experimental results reported previously. The optimum of the investigated molecular configuration indicates that the two hydrogen atoms attached to nitrogen atom have different activities due to their chemical environment; the relative energies of the ions in fragmentation pathway of ionized tetrahydroimidazole-substituted methylene beta-diketones provide indirectly an evidence for both the existence of ion/neutral complex and the stabilities of these ions.

Luminescence properties of the ternary rare earth complexes with beta-diketones and 1,10-phenanthroline incorporated in silica matrix by a sol-gel method

Ternary complexes of rare earth Eu(dbm)(3).phen and Tb(acac)(3).phen (dbm = dibenzoylmethanide, acac = acetylacetone and phen = 1,10-phenanthroline) were introduced into silica gel by the sol-gel method. The result indicated that the rare earth ions (EU3+ and Tb3+) showed fewer emission lines and slightly lower emission intensities in the silica gel than in the pure rare earth complexes. The lifetimes of rare earth ions in silica gel (Eu3+ and Tb3+) doped with Eu(dbm)(3).phen and Tb(acac)(3).phen were longer than those in purl Eu(dbm)(3).phen and Tb(acac)(3).phen. A very small amount of rare earth complexes doped in a silica gel matrix can retain excellent luminescence properties. (C) 1997 Elsevier Science S.A.

Synthesis, structure characterization and transesterification of the complexes of beta-alkoxycarbonylethyltin trichlorides

Thirteen title complexes ROCOCH2CH2SnCl3 . L(R = C(1 similar to 5)alkyl;L = DBSO,HMPA) were synthesized and characterized by elemental analysis, IR,H-1 NMR. The crystal structure of n -PrOCOCH2CH2SnCl3 . DBSO was determined by the X-ray diffraction analysis. The crystal belongs to orthorhombic system,space group P2(1)2(1)2(1) with a = 1.062, b = 1.427, c = 1.635nm; Z = 4. The complex exists as a discrete molecule, and the tin atom attains a distorted octahedral geometry via the coordination of intramolecular carbonyl oxygen and the Lewis base donor atom. The transesterification of CH3OCOCH2CH2SnCl3 . L with alcohol was studied, and the intramolecular Lewis acid catalytic mechanism was suggested.

Studies on the method of leaps and bounds regression

In this paper, we introduce the method of leaps and bounds regression which can be used to select variables quickly and obtain the best regression models. These models contain one variable, two variables, three variables and so on. The results obtained by using leaps and bounds regression were compared with those achieved by using stepwise regression to lead to the conclusion that leaps and bounds regression is an effective method.

Ion/neutral complex-mediated reactions generated from some ionized tetrahydroimidazole-substituted methylene beta-diketones

The dissociation of gaseous metastable ions of m/z 153 and the formation of ions of m/z 139 from the unimolecular fragmentations of ionized tetrahydroimidazole-substituted methylene beta-diketones were examined by tandem mass spectrometry. In addition, some other fragments accompanying the elimination of either an H2O molecule or an CHO. radical were also observed in the collision-induced dissociation spectra of molecular ions of the compounds bearing an aromatic ring. Collision-induced dissociation and isotopic labeling showed that these processes may involve reactions of intermediate ion/neutral complexes and multistep rearrangements. The corresponding mechanisms are discussed. (C) 1997 by John Wiley & Sons, Ltd.

Miscibility and crystallization of poly(beta-hydroxybutyrate) and poly(p-vinylphenol) blends

The miscibility and crystallization behavior of poly(beta-hydroxybutyrate) (PHB) and poly(p-vinylphenol) (PVPh) blends were studied by differential scanning calorimetry and optical microscopy (OM). The blends exhibit a single composition-dependent glass transition temperature, characteristic of miscible systems, A depression of the equilibrium melting temperature of PHB is observed. The interaction parameter values obtained from analysis of the melting point depression are of large negative values, which suggests that PHB and PVPh blends are thermodynamically miscible in the melt. Isothermal crystallization kinetics in the miscible blend system PHB/PVPh was examined by OM. The presence of the amorphous PVPh component results in a reduction in the rate of spherulite growth of PHB. The spherulite growth rate is analyzed using the Lauritzen-Hoffman model, The isothermally crystallized blends of PHB/PVPh were examined by wide-angle X-ray diffraction and smell-angle X-ray scattering (SAXS). The long period obtained from SAXS increases with the increase in PVPh component, which implies that the amorphous PVPh is squeezed into the interlamallar region of PHB.

The chemistry of alpha-oxo ketene cyclic dithioacetal .36. Studies on silica G catalyzed decomposition of adducts of beta,beta-1,3-propylenedithio-alpha,beta-unsaturated arylketones with grignard reagents

beta, beta-1, 3-Piopylenedithio-alpha, beta-unsaturated arylketones 2 via chemoselective 1,2-addition with allyl or benzyl Grignard reagents afforded the corresponding carbinols 3 and 4. Catalysed by silica gel, the carbinols 3 and 4 were converted to the beta,gamma-unsaturated arylketones 5, 6. The mechanism and reaction condition were discussed.

Compatibility and specific interactions in poly(beta-hydroxybutyrate) and poly(p-vinylphenol) blends

The miscibility and specific interactions in poly (beta-hydroxybutyrate) (PHB)/poly(p-vinylphenol) (PVPh) blends were studied by differential scanning calorimetry(DSC) , fourier transform infrared(FTIR) spectrometer and high resolution solid state C-13 NMR, A single composition-dependent glass transition temperatures were obtained by DSC which indicate the blends of PHB/PVPh were miscible in the melt state, The experimental glass transition temperatures were fitted quite well with those obtained from Couchman-Karasz equation. The FTIR study shows that the strong intermolecular hydrogen bonding exists in blends of PHB with strong proton acceptor and PVPh with strong proton donor and is the origin of its compatibility. The CPMAS C-13 NMR spectra also show that the strong hydrogen bonding exists in PHB/PVPh blends. From the T-1 rho(H) relaxation time it follows that the blends of PHB/PVPh(40/60, 20/80) studied are completely homogeneous on the scale of about 3.2 nm.

Study on the beta relaxation mechanism of thermosetting polyimide thermoplastic polyimide blends

The thermosetting polyimide PMR-I5 and its blends with thermoplastic polyimides have been studied by dynamic mechanical analysis. The results obtained indicate that the level of beta relaxations in PMR-15 are increased with an increase in cross-linking density. This phenomenon is interpreted as a change of chemical structure during the cross-linking process. Addition of thermoplastic polyimide makes the magnitude of beta relaxations increase when PMR-15 is the major component. This might be due to the strong intermolecular charge-transfer interaction between PI and PI or PMR-15 and PMR-15 molecular chains being partly replaced by the weak intermolecular interaction between PI and PMR-15 in PMR-15/PI blends, resulting in some phenylene rings or imide groups in PIs and PMR-15 chains being able to participate in beta relaxation. However, this increment in beta relaxation magnitude can be reduced by heat treatment of the sample, as a result of phase separation. Hence, it is concluded that the beta relaxation magnitude is determined by the number of groups which can participate in relaxation per unit length, i.e. the magnitude of beta relaxation increases with decreasing interaction between the molecular chains. Copyright (C) 1996 Elsevier Science Ltd

Synthesis and structures of the complexes of beta-alkoxycarbonylethyltin trichlorides with N-aryl-2-hydroxyacetophenylideneimines

Sixteen novel beta-alkoxycarbonylethyltin trichlorides and the corresponding N-aryl-2-hydroxyacetophenylideneimines complexes have been synthesized and characterized. An X-ray crystal structure analysis of the complex of beta-methyloxycarbonylethyltin trichloride and N-4-methylphenyl-2-hydroxyacetophenylideneimine has been performed, The crystal belongs to space group , The cell parameters are: a = 1.0201(6) nm, b = 1.082 2(4) nm, c = 1.394 9(6) nm, alpha = 99.88(3)degrees, beta = 98.63(4)degrees, gamma = 97.86(4)degrees, Z = 2, The ligands coordinate to tin atom via phenolic oxygen atom. Coordination of carbonyl oxygen atom to tin atom still exists in the complexes, The coordination number of tin atom is 6.

Prediction of molar absorptivities of color reagents during their color reactions with cerium using multiple regression analysis and neural network

A quantitative structure-property study has been made on the relationship between molar absorptivities (epsilon) of asymmetrical phosphone bisazo derivatives of chromotropic acid and their color reactions with cerium by multiple regression analysis and neural network. The new topological indices A(x1) - A(x3) suggested in our laboratory and molecular connectivity indices of 43 compounds have been calculated. The results obtained from the two methods are compared. The neural network model is superior to the regression analysis technique and gave a prediction which was sufficiently accurate to estimate the molar absorptivities of color reagents during their color reactions with cerium.

Study on Phenol Compounds Using Multiple Regression and Neural Network Methods

In this paper, the molecular connectivity indices and the electronic charge parameters of forty-eight phenol compounds nave been calculated. and applied for studying the relationship between partition coefficients and structure of phenol compounds. The results demonstrate that the properties of compounds can be described better with selective parameters, and the results obtained by neural network are superior to that by multiplle regression.