Thermo-Mechanical Properties of Semi-Degradable Poly(β-amino ester)-co-Methyl Methacrylate Networks under Simulated Physiological Conditions

Poly(β-amino ester) networks are being explored for biomedical applications, but they may lack the mechanical properties necessary for long term implantation. The objective of this study is to evaluate the effect of adding methyl methacrylate on networks’ mechanical properties under simulated physiological conditions. The networks were synthesized in two parts: (1) a biodegradable crosslinker was formed from a diacrylate and amine, (2) and then varying concentrations of methyl methacrylate were added prior to photopolymerizing the network. Degradation rate, mechanical properties, and glass transition temperature were studied as a function of methyl methacrylate composition. The crosslinking density played a limited role on mechanical properties for these networks, but increasing methyl methacrylate concentration improved the toughness by several orders of magnitude. Under simulated physiological conditions, networks showed increasing toughness or sustained toughness as degradation occurred. This work establishes a method of creating degradable networks with tailorable toughness while undergoing partial degradation.     

Molecular weight dependence of growth and morphology of it-poly(butene-1) spherulites

Molecular weight dependence of growth and morphology of spherulites of isotactic poly(butene-1), iPB-1, and those of the mixtures with atactic poly(butene-1), aPB-1, were examined by atomic force microscopy (AFM) and polarizing optical microscopy (POM) in order to examine the mechanism of the structural evolution by the branching and re-orientation of lamellar crystals at the growth front. The width of lamellar crystals and the characteristic size of the inner structure of spherulites decreased with increasing molecular weight. The result suggests that the mobility of the melt determines the sizes in spherulites and supports the growth front instability induced by a gradient triggering the branching. The sizes in the mixtures also decreased with increasing weight-averaged molecular weight, M_w. The size dependence in low M_w region, however, was too strong and that in high M_w was too weak in comparison with the predicted dependence for the prepared M_w. It has been concluded that the peculiar behaviors should be discussed with effective M_w influenced by the occurrence of separation and exclusion of non-crystallizing aPB-1 at the growth front.     

姬塬地区长2油层组储层岩石学特征研究

通过大量的岩心观察以及薄片鉴定,并以此为基础对该区储层岩石学特征进行了深入的研究。研究结果表明姬塬地区长2地层储层岩性以细粒长石砂岩和岩屑长石砂岩为主,储集砂岩的主要胶结物有高岭石、绿泥石、铁方解石及硅质,次为伊利石、铁白云石、方解石及长石质,姬塬地区长2砂岩分选中-好、次棱角状,以薄膜-孔隙及孔隙式胶结为主。     

超前注水机理综述

超前注水已经成为低渗透油藏开发的一种重要办法。超前注水在采油井投产前注水,提高地层初始压力,避免了压力降低过快造成的油藏渗透率下降,启动压力梯度增大和原油粘度增大,超前注水使压力梯度的升高,加快了渗流速度。另外,超前注水也能有效地防止指进现象,降低油井产量递减率,最终提高了油藏的采收率。     

Fe–Nx/C electrocatalysts synthesized by pyrolysis of Fe(II)–2,3,5,6-tetra(2-pyridyl)pyrazine complex for PEM fuel cell oxygen reduction reaction

2,3,5,6-Tetra(2-pyridyl)pyrazine (TPPZ) was employed as a ligand to prepare an iron(II) complex (Fe–TPPZ) that served as a precursor to synthesize carbon-supported catalysts (Fe–N_x/C) through heat-treatment at 600, 700, 800 and 900 °C under N₂ atmosphere. Both the structure and composition of the synthesized Fe–N_x/C were analyzed by X-ray diffraction and energy-dispersive X-ray microanalysis, respectively. The rotating disk and ring-disk electrode measurements showed that these catalysts have strong ORR activity with an overall 4-electron transfer process through a (2 + 2)-electron transfer mechanism, which was assigned to the catalytic function of the Fe–N_x center. A study on the heat-treatment temperature on the ORR activity showed that 800 °C is the optimal temperature for the synthesized catalysts. Furthermore, the effect of both catalyst and Nafion^® ionomer loadings in the catalyst layer on the corresponding ORR activity was also investigated. The kinetic parameters such as the chemical reaction rate between O₂ and Fe–N_x/C (adduct formation reaction), the rate constant for the rate-determining step (RDS), and the electron numbers in the ORR, were obtained. The methanol tolerance of the catalyst was also tested. To validate the ORR activity, a membrane electrode assembly in which the cathode catalyst layer contained Fe–N_x/C was constructed and tested in a real fuel cell. The results obtained are encouraging when compared with similar non-noble catalysts.     

Analysis of proton exchange membrane fuel cell catalyst layers for reduction of platinum loading at Nissan

The biggest issue that must be addressed in promoting widespread use of fuel cell vehicles (FCVs) is to reduce the cost of the fuel cell system. Especially, it is of vital importance to reduce platinum (Pt) loading of catalyst layers (CLs) in the membrane electrode assembly (MEA) of a proton exchange membrane fuel cell (PEMFC). In order to lower the Pt loading of the MEA, mass transport of reactants related to the performance in high current density should be enhanced significantly as well as kinetics of the catalyst, which can result in the better Pt utilization and effectiveness. In this study, we summarized our analytical approach and methods for reduction of Pt loading in CLs. Microstructure, mass transport properties of the reactants, and their relation in CLs were elucidated by applying experimental analyses and computational methods. A simple CL model for I–V performance prediction was then established, where experimentally elucidated parameters of the microstructure and the properties in CLs were taken into account. Finally, we revealed the impact of lowering the Pt loading on the transport properties, polarization, and the I–V performance.     

Parameter optimization for the Gaussian model of protein folding

Computational models of protein folding and ligand docking are large and complex. Few systematic methods have yet been developed to optimize the parameters in such models. We describe here an iterative parameter optimization strategy that is based on minimizing a structural error measure by descent in parameter space. At the start, we know the ‘correct’ native structure that we want the model to produce, and an initial set of parameters representing the relative strengths of interactions between the amino acids. The parameters are changed systematically until the model native structure converges as closely as possible to the correct native structure. As a test, we apply this parameter optimization method to the recently developed Gaussian model of protein folding: each amino acid is represented as a bead and all bonds, covalent and noncovalent, are represented by Hooke's law springs. We show that even though the Gaussian model has continuous degrees of freedom, parameters can be chosen to cause its ground state to be identical to that of Go-type lattice models, for which the global ground states are known. Parameters for a more realistic protein model can also be obtained to produce structures close to the real native structures in the protein database.     

Miscibility and morphology in crystalline/amorphous blends of poly(caprolactone)/poly(4-vinylphenol) as studied by DSC, FTIR, and C solid state NMR

The miscibility and morphology of poly(caprolactone) (PCL) and poly (4-vinylphenol) (PVPh) blends were investigated by using differential scanning calorimetry (DSC), Fourier transform infrared (FTIR) spectroscopy and ¹³C solid state nuclear magnetic resonance (NMR) spectroscopy. The DSC results indicate that PCL is miscible with PVPh. FTIR studies reveal that hydrogen bonding exists between the hydroxyl groups of PVPh and the carbonyl groups of PCL. ¹³C cross polarization (CP)/magic angle spinning (MAS)/dipolar decoupling (DD) spectra of the blends show a 1 ppm downfield shifting of ¹³C resonance of PVPh hydroxyl-substituted carbons and PCL carbonyl carbons with increasing PCL content. Both FTIR and NMR give evidence of inter-molecular hydrogen bonding within the blends. The proton spin-lattice relaxation in the laboratory frame, T₁(H), and in the rotating frame, T_1ρ(H), were studied as a function of the blend composition. The T₁(H) results are in good agreement with thermal analysis; i.e. the blends are completely homogeneous on the scale of 50-80 nm. The T_1ρ(H) results indicate that PCL in the blends has both crystalline and amorphous phases. The amorphous PCL phase is miscible with PVPh, but the PCL crystal domain size is probably larger than the spin-diffusion path length within the T_1ρ(H) time-frame, i.e. larger than 2-4 nm. The mobility differences between the crystalline and amorphous phases of PCL are clearly visible from the T_1ρ(H) data.     

Toughening of cycloaliphatic epoxy resins by poly(ethylene phthalate) and related copolyesters

Poly(ethylene phthalate) (PEP) and poly(ethylene phthalate–co‐ethylene terephthalate) were used to improve the brittleness of the cycloaliphatic epoxy resin 3,4‐epoxycyclohexylmethyl 3,4‐epoxycyclohexane carboxylate (Celoxide 2021?), cured with methyl hexahydrophthalic anhydride. The aromatic polyesters used were soluble in the epoxy resin without solvents and effective as modifiers for toughening the cured epoxy resin. For example, the inclusion of 20 wt % PEP (MW, 7400) led to a 130% increase in the fracture toughness (K_IC) of the cured resin with no loss of mechanical and thermal properties. The toughening mechanism is discussed in terms of the morphological and dynamic viscoelastic behaviors of the modified epoxy resin system. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 388–399, 2002; DOI 10.1002/app.10363     

Enhanced strain hardening in elongational viscosity for HDPE/crosslinked HDPE blend. I. Characteristics of crosslinked HDPE

Blending a crosslinked high‐density polyethylene (xHDPE) enhances melt strength and strain hardening behavior in elongational viscosity of high‐density polyethylene (HDPE) to a great degree. Gel fraction of xHDPE has a stronger effect on the strain hardening than sol fraction, although sol fraction also enhances the strain hardening to some degree. Further, the xHDPE crosslinked by peroxide in a compression mold exhibits more pronounced effect than xHDPE by radiation, which is attributed to the difference in the amount of the gel fraction. The xHDPE, which enhances the strain hardening, has sparse crosslink points in the network. Moreover, it was found from linear viscoelastic measurements, such as oscillatory modulus and relaxation modulus, that the xHDPE is characterized as a critical gel, which was also supported by the result of tensile testing. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 73–78, 2002