离子液体在金属催化剂作用下的羰基化反应中的应用

离子液体是许多有机反应的优良溶剂,能够溶解许多包括金属有机化合物在内的有机物。本文重点综述了离子液体在金属催化剂作用下的羰基化反应中的应用进展。     

Crystal Structure and Elastic Properties of Hypothesized MAX Phase‐Like Compound (Cr2Hf)2Al3C3

The term “MAX phase” refers to a very interesting and important class of layered ternary transition‐metal carbides and nitrides with a novel combination of both metal and ceramic‐like properties that have made these materials highly regarded candidates for numerous technological and engineering applications. Using (Cr₂Hf)₂Al₃C₃ as an example, we demonstrate the possibility of incorporating more types of elements into a MAX phase while maintaining the crystallinity, instead of creating solid solution phases. The crystal structure and elastic properties of MAX phase‐like (Cr₂Hf)₂Al₃C₃ are studied using the Vienna ab initio Simulation Package. Unlike MAX phases with a hexagonal symmetry (P6₃/mmc, #194), (Cr₂Hf)₂Al₃C₃ crystallizes in the monoclinic space group of P2₁/m (#11) with lattice parameters of a = 5.1739 Å, b = 5.1974 Å, c = 12.8019 Å; α = β = 90°, γ = 119.8509°. Its structure is found to be energetically much more favorable with an energy (per formula unit) of ?102.11 eV, significantly lower than those of the allotropic segregation (?100.05 eV) and solid solution (?100.13 eV) phases. Calculations using a stress versus strain approach and the VRH approximation for polycrystals also show that (Cr₂Hf)₂Al₃C₃ has outstanding elastic moduli.     

Polyampholyte acrylic latexes for tablet coating applications

Polyampholyte latexes can exist within a certain pH range as low‐viscosity aqueous dispersions, while upon a pH shift to the vicinity of the isoelectric point they undergo ionic coacervation. Three classes of coacervation latexes were synthesized and evaluated for their suitability for use in tablet coating applications. Pharmaceutical tablet coatings are commonly based on hydroxypropyl methyl cellulose, poly(vinyl alcohol), and acrylic polymers. Because of the high viscosity of their aqueous solutions, and to the consequent required low concentrations of the tablet coating polymers in the coating solutions to enable sufficiently low viscosity for effective spray application, the current commercial pharmaceutical tablet coating technology requires the removal of large amounts of water during the manufacturing process. In this work, films prepared from high‐solids, low‐viscosity coacervated acrylic latexes showed good hardness, very low tackiness, an excellent combination of optical properties, and very low water vapor permeability. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40049.     

PMMA composites of single‐walled carbon nanotubes‐graft‐PMMA

To facilitate the dispersion of single‐walled carbon nanotubes (SWCNT) into poly(methyl methacrylate) (PMMA), SWCNT were functionalized with a RAFT chain transfer agent, and PMMA was grafted from the SWCNT by reversible addition–fragmentation transfer (RAFT) polymerization to give SWCNT‐g‐PMMA containing 6 wt % PMMA. SWCNT‐g‐PMMA in the form of small bundles was dispersed into PMMA matrices. The SWCNT‐g‐PMMA filler increased the glass transition temperature (T_g) of the composite when the matrix molecular weight M_n was less than the graft molecular weight, but not when the matrix M_n was equal to or greater than the graft M_n. The threshold of electrical conductivity of the composites as a function of weight percent SWCNT increased from 0.2% when matrix M_n was less than graft M_n to about 1% when matrix M_n was greater than graft M_n. Dynamic mechanical analyses of the composites having graft M_n less than or equal to matrix M_n showed broader rubbery plateaus with increased SWCNT content but no significant differences between samples with different grafted PMMAs. The results indicate that lower M_n matrix wets the SWCNT‐g‐PMMA whereas higher M_n matrix does not wet the SWCNT‐g‐PMMA. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39884.     

Strength improvements in toughened epoxy composites using surface treated GnPs

Nanographitic materials are gaining enormous interest as a new class of reinforcement for nanocomposites, promising revolutionary electrical, thermal, and mechanical properties. However, the progress has been quite limited especially in terms of mechanical properties. Here we report a significant leap, >2× increases in tensile strength and modulus of an epoxy composite using surface treated graphite nanoplatelets (GnPs). This corroborated by increases in Tgs as well as the presence of oxygen‐functionalized groups verified by XPS, suggest improved distribution and chemical interaction at the filler‐to‐matrix interface. Toughness values also showed increases with concentration, without compromising the strength or failure strain. However, if solvent levels during degassing were not reduced sufficiently, negligible contributions to strength and stiffness were observed with GnP loading. Subsequent elevated temperature treatments increased the strength of the composite due to cure enhancement of the matrix material, yet did not provide mechanical enhancements due to the incorporation of the filler. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40802.     

Developing toughened aromatic polybenzoxazines using thermoplastic oligomers and telechelics,part 1: Preparation and characterization of the functionalized oligomers

The preparation and characterization of three families of thermoplastic oligomers (M_n = 2918–13263 g mol^?1) based on polyarylsulfone (PSU) differing in both molecular weight and terminal functionality and one series of polyarylethersulfone (PES) of different molecular weights is reported. Infrared and nuclear magnetic resonance spectroscopy data support the formation of both the hydroxyl terminated oligomers and conversion (67–89% depending on molecular weight) to the telechelic PSU oligomer bearing reactive benzoxazine groups. Differential scanning calorimetry reveals that the onset of homopolymerization in the telechelic PSU oligomer occurs at around 100°C (peak maximum 125°C at 10 K/min) and rescans show values of the glass transition (for the homopolymers) ranging from 124 to 167°C depending on molecular weight. The influence on the oligomer backbone and terminal functionality is examined using thermal analysis. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40875.     

Uricase-immobilization on radiation grafted polymer support for detection of uric acid using Ag-nanoparticle based optical biosensor

A functional polymer support was designed for covalent immobilization of enzyme uricase, which was further utilized in a single enzyme based silver nanoparticles (Ag-NPs)-optical biosensor system for estimation of uric acid. A carboxylic acid functionalized polymer support was fabricated via gamma radiation induced mutual-irradiation grafting of polyacrylic acid (PAA) on to non-woven polypropylene (PP) matrix. Grafting parameters, such as dose, monomer concentration, homopolymer inhibitor and inorganic acid concentration were studied to optimize the grafting process. PAA-g-PP samples were characterized by grafting yield measurement, water uptake, FTIR, TGA and SEM techniques. Uricase enzyme was immobilized on to the PAA-g-PP support via covalent amide linkage using coupling agents, namely N-hydroxysuccinimide (NHS) and N-ethyl-N′-(3-(dimethylamino)propyl)carbodiimide (EDC). The catalytic activity of uricase was investigated spectrophotometrically using uric acid as a substrate. Study of kinetic parameters (K_m, V_max) revealed the value of K_m for covalently immobilized uricase to be ∼1.2-fold higher than that of free enzyme. The uricase-immobilized-PAA-g-PP samples could be repeatedly used for ∼20 cycles over a period of 30 days when stored in phosphate buffer (pH∼7.4) at 4°C without significant decrease in the enzyme activity. The uricase immobilized samples were successfully used in conjunction with the radiolytically synthesized Ag-NPs as a LSPR-optical biosensor for estimation of uric acid.     

Functional mesoporous poly(ionic liquid)-based copolymer monoliths: From synthesis to catalysis and microporous carbon production

Ionic liquid-functionalized mesoporous polymeric networks with specific surface area up to 935 m²/g have been successfully synthesized one pot by solvothermal copolymerization of divinylbenzene and monomeric ionic liquids. The as-obtained polymers exhibit a monolithic structure featuring large pore volumes, an abundant mesoporosity and an adjustable content of ionic liquids. The effect of the reaction conditions on the pore structure has been studied in detail. These poly(ionic liquid)-based porous networks (PILPNs) have then been employed as precursors in two distinct applications, namely organocatalysis and production of microporous carbon monoliths. Selected organocatalyzed reactions, including carbonatation of propylene oxide by cycloaddition with carbon dioxide, benzoin condensation, and cyanosilylation of benzaldehyde have been readily triggered by PILPNs acting as crosslinked polymer-supported (pre)catalysts. The two latter reactions required the prior deprotonation of the imidazolium salt units with a strong base to successfully generate polymer-supported N-heterocyclic carbenes, referred to as poly(NHC)s. Facile recycling and reuse of polymer-supported (pre)catalysts was achieved by simple filtration owing to the heterogeneous reaction conditions. Furthermore, PILPNs could be easily converted into microporous carbon monoliths via CO₂ activation.     

In vitro evaluation of spray‐dried chitosan microspheres crosslinked with pyromellitic dianhydride for oral colon‐specific delivery of protein drugs

Chitosan microspheres have been prepared using a spray‐drying method, and crosslinked with pyromellitic dianhydride. The chemical structure of the modified chitosan was characterized by FTIR spectroscopy and solid state 13C NMR analysis. The particle size and morphology of the crosslinked chitosan were investigated. These microspheres were evaluated for colon‐specific delivery of bovine serum albumin (BSA) as a model protein drug. The results indicate that the drug was released as follows: 37.1 ± 2.8% after 2 h in SGF, 73.1 ± 4.8% after 8 h (2 h in SGF+ 6 h in SIF), and 80.9 ± 4.1% after 12 h in SCF. The effect of β‐glucosidase on the drug release was also examined. The encapsulation efficiency was decreased from 88.4 ± 3.1% to 62.8 ± 2.9%, with increasing BSA concentration. Loading capacity was significantly increased from 6.3 ± 0.3% to 41.8 ± 4.1% by increasing the initial BSA concentration. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40514.