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Novel Initiator (novel + initiator)
Selected AbstractsLanthanide Thiolate Complexes: Novel Initiators for Ring-opening Polymerization of ,-CaprolactoneCHINESE JOURNAL OF CHEMISTRY, Issue 11 2005Hong-Mei Sun Abstract The ring-opening polymerization (ROP) of , -caprolactone (, -CL) using lanthanide thiolate complexes [(CH3C5H4)2Sm(,-SPh)(THF)] 2 (1) and Sm(SPh)3(HMPA)3 (2) as initiators has been investigated for the first time. Both of 1 and 2 were found to be highly efficient initiators for the ROP of , -CL. The poly(, -caprolactone) (PCL) with molecular weight Mn up to 1.97×105 and relatively narrow molecular weight distributions (1.20< Mw/Mn<2.00) have been obtained in high yield in the temperature range of 35,65 °C. According to the polymer yield, 2 showed much higher activity than 1. However, the number-average molecular weight of PCL obtained with 2 was much lower than with 1. The possible polymerization mechanism of the , -CL polymerization has been proposed based on the results of the end group analysis of the , -CL oligomer. [source] Alternating copolymerization of carbon dioxide and epoxide catalyzed by an aluminum Schiff base,ammonium salt systemJOURNAL OF POLYMER SCIENCE (IN TWO SECTIONS), Issue 18 2005Hiroshi Sugimoto Abstract The alternating copolymerization of carbon dioxide (CO2) and cyclohexene oxide (CHO) with an aluminum Schiff base complex in conjunction with an appropriate additive as a novel initiator is demonstrated. A typical example is the copolymerization of CO2 and CHO with the (Salophen)AlMe (1a),tetraethylammonium acetate (Et4NOAc) system. When a mixture of the 1a,Et4NOAc system and CHO was pressurized by CO2 (50 atm) at 80 °C in CH2Cl2, the copolymerization of CO2 and CHO took place smoothly and produced a high polymer yield in 24 h. From the IR and NMR spectra, the product was characterized to be a copolymer of CO2 and CHO with an almost perfect alternating structure. The matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis indicated that an unfavorable reaction between Et4NOAc and CH2Cl2 and a possible chain-transfer reaction with concomitant water occurred, and this resulted in the bimodal distribution of the obtained copolymer. With carefully predried reagents and apparatus, the alternating copolymerization in toluene gave a copolymer with a unimodal and narrower molecular weight distribution. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 4172,4186, 2005 [source] Integrating art as a trans-boundary element in a radical innovation frameworkR & D MANAGEMENT, Issue 1 2010Christian Stüer Companies have learned that radical innovations (RIs) are a prerequisite to grow organically. However, companies struggle to identify and introduce RIs, as their inherent high uncertainties and novelty challenge established organisations and management routines. To address the first challenge, companies need to take a holistic approach and design a trans-boundary environment of creativity, trans-disciplinary and entrepreneurial spirit. This environment attracts and retains visionary people, fosters generation of new opportunities and cultivates adaptability. By adapting evaluation metrics for RI, setting up flexible processes, and promoting trans-disciplinary exchange, the second challenge can be addressed. Increased research has concentrated on several aspects of RI lately, but so far a combining framework is missing. Our paper bridges this gap by developing an improved theoretical framework, enhancing the existing literature and introducing art as a method to advance trans-disciplinary interchange. In a case-study approach, we have applied our framework to the research and development department of Vodafone Research and Development, Germany, as they integrate art methodically in their research and development process. Analysing their RI capabilities, we identify the trans-disciplinary exchange with artists as a novel initiator and driver of RI, which has not yet been adequately considered. [source] Matriptase is a novel initiator of cartilage matrix degradation in osteoarthritisARTHRITIS & RHEUMATISM, Issue 7 2010Jennifer M. Milner Objective Increasing evidence implicates serine proteinases in pathologic tissue turnover. The aim of this study was to assess the role of the transmembrane serine proteinase matriptase in cartilage destruction in osteoarthritis (OA). Methods Serine proteinase gene expression in femoral head cartilage obtained from either patients with hip OA or patients with fracture to the neck of the femur (NOF) was assessed using a low-density array. The effect of matriptase on collagen breakdown was determined in cartilage degradation models, while the effect on matrix metalloproteinase (MMP) expression was analyzed by real-time polymerase chain reaction. ProMMP processing was determined using sodium dodecyl sulfate,polyacrylamide gel electrophoresis/N-terminal sequencing, while its ability to activate proteinase-activated receptor 2 (PAR-2) was determined using a synovial perfusion assay in mice. Results Matriptase gene expression was significantly elevated in OA cartilage compared with NOF cartilage, and matriptase was immunolocalized to OA chondrocytes. We showed that matriptase activated proMMP-1 and processed proMMP-3 to its fully active form. Exogenous matriptase significantly enhanced cytokine-stimulated cartilage collagenolysis, while matriptase alone caused significant collagenolysis from OA cartilage, which was metalloproteinase-dependent. Matriptase also induced MMP-1, MMP-3, and MMP-13 gene expression. Synovial perfusion data confirmed that matriptase activates PAR-2, and we demonstrated that matriptase-dependent enhancement of collagenolysis from OA cartilage is blocked by PAR-2 inhibition. Conclusion Elevated matriptase expression in OA and the ability of matriptase to activate selective proMMPs as well as induce collagenase expression make this serine proteinase a key initiator and inducer of cartilage destruction in OA. We propose that the indirect effects of matriptase are mediated by PAR-2, and a more detailed understanding of these mechanisms may highlight important new therapeutic targets for OA treatment. [source] Copolymerization of Cyclohexene Oxide with CO2 by Using Intramolecular Dinuclear Zinc CatalystsCHEMISTRY - A EUROPEAN JOURNAL, Issue 12 2005Youli Xiao Abstract The intramolecular dinuclear zinc complexes generated in situ from the reaction of multidentate semi-azacrown ether ligands with Et2Zn, followed by treatment with an alcohol additive, were found to promote the copolymerization of CO2 and cyclohexene oxide (CHO) with completely alternating polycarbonate selectivity and high efficiency. With this type of novel initiator, the copolymerization could be accomplished under mild conditions at 1 atm pressure of CO2, which represents a significant advantage over most catalytic systems developed for this reaction so far. The copolymerization reaction was demonstrated to be a living process as a result of the narrow polydispersities and the linear increase in the molecular weight with conversion of CHO. In addition, the solid-state structure of the dinuclear zinc complex was characterized by X-ray crystal structural analysis and can be considered as a model of the active catalyst. On the basis of the various efforts made to understand the mechanisms of the catalytic reaction, including MALDI-TOF mass analysis of the copolymers' end-groups, the effect of alcohol additives on the catalysis and CO2 pressure on the conversion of CHO, as well as the kinetic data gained from in situ IR spectroscopy, a plausible catalytic cycle for the present reaction system is outlined. The copolymerization is initiated by the insertion of CO2 into the ZnOEt bond to afford a carbonate,ester-bridged complex. The dinuclear zinc structure of the catalyst remains intact throughout the copolymerization. The bridged zinc centers may have a synergistic effect on the copolymerization reaction; one zinc center could activate the epoxide through its coordination and the second zinc atom may be responsible for carbonate propagation by nucleophilic attack by the carbonate ester on the back side of the cis -epoxide ring to afford the carbonate. The mechanistic implication of this is particularly important for future research into the design of efficient and practical catalysts for the copolymerization of epoxides with CO2. [source] | ||||||||||