Synthesis and characterization of biodegradable block copolymer pluronic‐b‐poly(L‐lysine)

This study presented the investigations on the synthesis of a novel biodegradable block copolymer of pluronic‐b‐poly(L ‐lysine) (pluronic‐b‐PLL), which combined the characteristics of aliphatic polyester and poly(amino acids). The synthesis work started with end‐capping of pluronic with N‐t‐butoxycarbonyl‐L ‐phenylalanine using dicyclohexylcarbodiimide in the presence of 4‐dimethylaminopyridine, followed by a deprotection process to obtain the amino‐terminated pluronic; the new primary amino group in the modified pluronic initiated ring‐opening polymerization of amino acid N‐carboxyanhydride, which afforded the pluronic‐b‐poly(N^ε‐(Z)‐L ‐lysine) block copolymer. Finally, removal of the side‐chain N^ε‐(carbonybenzoxy) end protecting groups yields the block copolymer of pluronic‐b‐PLL. The products were characterized by ¹H‐NMR, FTIR, DSC, and GPC. The block copolymer micelle containing the anticancer drug paclitaxel was prepared by the double emulsion method. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Characterization of enzyme‐deproteinized skim rubber

Skim natural rubber latex is a protein‐rich byproduct obtained during the centrifugal concentration of natural rubber latex. Skim latex has a very low dry rubber content (4–8%), and the rubber particles are smaller in size. It has a higher proportion of nonrubber solids, which are mostly proteinaceous in nature. It is difficult to coagulate, and it takes more processing time. The proteins in skim latex can be decomposed by proteolytic enzymes. This article discusses the use of stabilized liquid papain from the papaya plant (Carica papaya) for deproteinization followed by creaming for quick and easy coagulation of skim latex. The technological properties and aging characteristics of the deproteinized skim rubber are compared with those of conventionally prepared skim rubber and block rubber. The deproteinized skim rubber showed enhanced quality parameters. Particle size analysis revealed that deproteinization and creaming of the skim latex did not markedly change the particle size. Gel permeation chromatography showed a reduction in the quantity of fatty acids after deproteinization and creaming, which was reflected in the improvement of the aging characteristics in comparison with the control sample. Vulcanizates prepared with the deproteinized skim rubber had higher resilience, lower heat buildup, lower compression set, and good tensile strength and elongation at break in comparison with conventionally prepared skim rubber, and the properties were almost comparable to those of block rubber. The improvement in the mechanical properties and aging characteristics could be attributed to the reduction of the protein content, the partial removal of unsaturated fatty acids, and the removal of metal ions that were pro‐oxidants during the deproteinization and creaming process. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Simultaneous continuous,nonchromatographic monitoring and discrete chromatographic monitoring of polymerization reactions

Automatic continuous nonchromatographic monitoring and discrete chromatographic monitoring were coupled together for the first time and used to monitor free radical and controlled‐radical polymerization reactions. This was achieved by adding a multidetector Size Exclusion Chromatography (SEC) system (alternatively termed Gel Permeation Chromatography, GPC) to the ACOMP platform (Automatic Continuous Online Monitoring of Polymerization reactions). The fact that the reactor solution is already preconditioned in the ACOMP front‐end to the concentration levels used in SEC makes direct coupling possible. Kinetics from two different types of reactions, Reversible Addition Fragmentation Transfer (RAFT) and free radical polymerization of butyl acrylate were studied, including the production of a bimodal population. Complementary and contrasting features from the continuous and SEC approaches are highlighted. The main advantage of the SEC detection is to follow the evolution of full molecular weight distributions (MWD), especially in ‘living’ type reactions, where polydispersity decreases with monomer conversion, whereas the continuous detection provides a much more detailed characterization of the reaction. Interestingly, in the case where a bimodal molecular weight distribution was produced, the continuous method automatically detected the onset of the second mode in a model independent fashion, whereas SEC could only discern the bimodality by applying preconceived models. The SEC approach will have valuable niche applications, however, such as when reactions are relatively slow, monitoring narrow polydispersity is of primary importance, and also in copolymerization and terpolymerization reactions where complex mixtures of reagents (e.g., RAFT agents, copper ions, etc.) make unfractionated spectroscopic resolution of comonomers difficult. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Methyl acrylate/1‐octene copolymers: Lewis acid‐mediated polymerization

Copolymerization of methyl acrylate (MA) with 1‐octene (1‐Oct) was conducted in the presence of free radical initiator, 2,2′‐azobis(2‐methylpropionitrile) (AIBN) using heterogeneous Lewis acid, acidic alumina. The polymers obtained were transparent and highly viscous liquids. The copolymer composition calculated from ¹H NMR showed alkene incorporation in the range of 10–61%. The monomodal nature of chromatographic curves corresponding to the molecular weight distribution in gel permeation chromatography (GPC) further confirmed that the polymers obtained are true copolymers. The number–average molecular weights (M_n) of the copolymers were in the range of 1.1 × 10⁴–1.6 × 10⁴ with polydispersity index of 1.75–2.29. The effects of varying the acidic alumina amount, time of polymerization, and monomer infeed on the incorporation of 1‐Oct in the polymer chain were studied. Increased 1‐Oct infeed led to its higher inclusion in the copolymer chain as elucidated by NMR. DEPT‐135 NMR spectral analysis was used to explicate the nature of arrangement of monomer sequences in the copolymer chain. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Fabrication of ultrathin La0.6Sr0.4Co0.2Fe0.8O3-δ hollow fibre membranes for oxygen permeation

An ultrathin La_0.6Sr_0.4Co_0.2Fe_0.8O_3-δ (LSCF) hollow fibre membrane for enhanced oxygen permeation flux was fabricated using a wet spinning/sintering method. The membrane exhibits a highly asymmetric structure comprising of a very thin dense outer layer supported by finger-like structures that are fully open on the inner surface. Oxygen permeation measurements were conducted using sweep gas as an operating mode. Effects of operating temperatures and flow rates of the sweep gas on the oxygen permeation fluxes were investigated in details. The highest oxygen permeation flux, i.e. 0.096 cm³/cm² s (5.77 cm³/cm² min) was obtained from the ultrathin hollow fibre membrane at 1323 K (1050 °C) and the sweep gas flow rate of 2.42 cm³/s. The results indicate that the oxygen permeation flux obtained is much higher (4.9-11.2 times) than that obtained from conventional LSCF hollow fibre membranes mainly due to the reduced thickness of the membrane as well as the porous surface on the permeate side. In addition, despite a very thin dense layer, the LSCF hollow fibre membrane possessed a reasonable mechanical strength (113.22 MPa).     

溶液混合与界面渗透法制备聚噻吩衍生物/聚酰亚胺导电复合材料的研究

本文介绍了高分子溶液混合与界面渗透法制备导电高分子复合材料的方法并对复合材料的结构和性能进行了表征.十二烷基取代聚噻吩四氢呋喃溶液与聚酰亚胺酸N-甲基吡咯烷酮在一定时间界面的互相渗透,十二烷基取代聚噻吩可嵌入聚酰亚胺酸层中.在溶剂挥发后,用化学或加热的方法进行酰胺化而得到稳定的导电高分子复合膜.表面电阻率、热失重及扫描电镜分析表明,与溶液混合法相比,界面渗透法制备的复合材料具有良好导电性能和稳定性.     

Vanadium carbide coating as hydrogen permeation barrier: A DFT study

Density functional calculations are used to investigate hydrogen (H) behaviors in vanadium carbide (VC). Molecular H₂ dissociation, atomic H diffusion and penetration are analyzed using the transition state theory. H₂ prefers to be close to the surface as physical adsorption, providing an environment conducive for further dissociation, and dissociates into atomic H adsorbed at the top C atom sites with co-adsorption state. The dissociation rate on the surface is mainly limited by the temperature-controlled activation energy barrier. The adsorptivity of atomic H by the surface tends to decrease as increasing of H coverage. For atomic H penetration through the surface, a significantly endothermic energy barrier and the low diffusion prefactor suggest that the main resistant effect of H permeation takes place at the surface. Energetic, vibrational, electronic consequences, and quantum effects on the H behaviors are discussed thoroughly. Our theoretical investigation indicates VC is a promising hydrogen permeation barrier.     

Effects of rolling and annealing on hydrogen permeability and crystal orientation in Nb-TiNi two-phase alloys

The Nb₁₉Ti₄₀Ni₄₁ alloy has a lamellar structure with bcc-Nb and B2-TiNi phases. It is known that a granule Nb phase forms in the TiNi matrix after thermal annealing and that the hydrogen permeability of unrolled annealed alloy is higher than that of rolled annealed alloy, even though the two alloys have granule Nb phase. Although the “cube-on-cube” relationship of crystal orientation for these phases has been observed in unrolled annealed alloy, no specific crystal orientation relationship has been seen in rolled annealed alloy. This indicates that the crystal orientation between the two phases strongly affects hydrogen permeability in Nb-TiNi two-phase alloys.     

A rational asymmetric hollow fiber membrane for oxygen permeation

A typical oxygen permeation hollow fiber membrane fabricated by phase inversion-based extrusion process demonstrates heterogeneous porous microstructures, in which the surface layer with relatively low porosity is used as a separation layer after sintering. It is usually not convenient to control the thickness of separation layer. And a high sintering temperature is needed to densify the separation layer, which in turn could destroy the desired porous microstructures in other portion. This paper studies a novel process to fabricate multilayer asymmetric hollow fiber membrane with a rational design using 67 vol. % Gd_0.2Ce_0.8O_2−δ−33 vol. % La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ (GDC-LSCF) as a model material system. The phase inversion-based extrusion process in open literature is employed to fabricate a hollow fiber substrate featuring radially well-aligned microchannels open at the inner surface. Built upon the hollow fiber substrate, a thin dense separation layer and porous surface catalyst layer at shell side are then fabricated through dip-coating and sintering process alternatively. The oxygen permeation flux of the fabricated hollow fiber membrane reaches 2.68 mL/cm²/min at 900°C under Ar/air gradient, the highest performance of the membranes with GDC-LSCF material system in open literature. The innovative fabrication process is able to readily control the thickness of functional layers while decreasing sintering temperatures.     

金属有机骨架膜的制备与应用进展

膜分离技术因其高效节能的特点,被认为是最有前景的分离技术之一。由于众多待分离的混合组分在物理性质（如尺寸）上极为接近,实现精确的膜分离仍具有极大的挑战。金属有机骨架材料具有孔径精确可调、孔隙率高等优点,使其有望实现对尺寸相近分子的精确筛分,因此可以作为理想的膜材料。本文对传统的多孔膜材料进行了比较,并对基于金属有机骨架材料的多孔膜进行了分类,包括支撑型金属有机骨架膜和混合基质膜。同时,系统地总结了两大类金属有机骨架膜的制备方法及其发展历程,对先进的膜制备技术进行了展望;总结了金属有机骨架膜在气体分离、纳滤及海水淡化、渗透汽化等方面的应用。最后,针对支撑型金属有机骨架膜提出了改善其透量和选择性的思路。