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991.
Tonimar DA Senra Danilo M Santos Jacques Desbrières Sergio P Campana‐Filho 《Polymer International》2015,64(11):1617-1626
The effects of reaction time, concentration of aqueous sodium hydroxide and molar ratio iodomethane/chitosan on the yield of the reaction of chitosan with iodomethane in N‐methyl‐2‐pyrrolidone (NMP) at 25.0 ± 0.1 °C, as well as on the characteristics of the resulting N,N,N‐trimethylchitosan (TMCh), were evaluated by using full‐factorial 23 design analysis and response surface methodology. This study also aimed to determine the reaction conditions allowing the production of water‐soluble TMCh presenting a high average degree of quaternization and intrinsic viscosity at high reaction yield. 1H NMR spectroscopy was employed for structural characterization, including the determination of average degrees of acetylation () and quaternization (), while capillary viscometry was used to determine intrinsic viscosity [η]. The results show that when the extensive N‐methylation is carried out for 24 h in NMP/15% NaOH (w/v) employing a lower excess of iodomethane (CH3I/Ch = 9), water‐soluble highly substituted ( = 46.0%) TMCh ([η] = 213.0 mL g?1) can be produced in high yield (81.8%). The highly significant mathematical models resulting from this study describe the dependence of the experimental responses on the reaction conditions and allow the characteristics and properties of the resulting TMCh to be defined by properly choosing the reaction conditions. © 2015 Society of Chemical Industry 相似文献
992.
设计了一种基于嵌入式ARM微控制器的N＋1自动切换控制系统,将高速CAN通信应用到N＋1自动切换控制系统中,减少各控制器之间交换信息的时间．利用嵌入式技术,降低了系统的成本;利用专门配备的测控模块,提高了系统的可靠性．该系统可以实现一台备机为多台主机备份以及主备发射机自动切换． 相似文献
993.
Erna Xun Jiaxin Wang Hong Zhang Ge Chen Hong Yue Zhi Wang 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2013,88(5):904-909
BACKGROUND: The enantiomers of N‐hydroxymethyl vince lactam are important intermediates during the synthesis of chiral drugs. The preparation of its single enantiomer can be performed through enzymatic resolution. The aim of this work is to obtain (1S, 4R)‐N‐hydroxymethyl vince lactam with high enantiomeric purity via lipase‐catalyzed enantioselective transesterification in organic solvents. To achieve this, effects of various reaction conditions (including lipase sources, acyl donor, substrate molar ratio, organic solvent, temperature, and water activity) on the enzyme activity as well as enantioselectivity were investigated. RESULTS: The results of the study showed that the enantiopreference for all the selected enzymes was (4S, 1R)‐N‐hydroxymethyl vince lactam in enantioselective transesterification of racemic N‐hydroxymethyl vince lactam. Under the selected optimum conditions, the highest enantioselectivity (E = 33.8) was obtained with a higher enzyme activity (20.3 µmol g?1 min?1) for Mucor miehei lipase (MML) when vinyl valerate was used as the acyl donor. Besides, the remained (1S, 4R)‐N‐hydroxymethyl vince lactam with high enantiomeric purity (ee > 99%) was obtained when the conversion was about 60%. CONCLUSION: The results obtained clearly demonstrated potential for industrial application of lipase in resolution of N‐hydroxymethyl vince lactam through enantioselective transesterification. © 2012 Society of Chemical Industry 相似文献
994.
995.
Min Jia Hongmin Cui Weiqun Jin Lili Zhu Yu Liu Ji Chen 《Journal of chemical technology and biotechnology (Oxford, Oxfordshire : 1986)》2013,88(3):437-443
BACKGROUND: Rhenium is a rare and valuable metal coexisting with molybdenum in molybdenite and sulfide copper ores and is hard to separate. Methods such as solvent extraction, ion exchange, adsorption, precipitation, etc. have been used to separate and purify Re(VII), and resin ion exchange has been widely investigated and used owing to its convenient operation and relatively low‐cost. The main challenge comes from the preparation of resins having high performance and stability. In an earlier study, an N‐methylimidazolium functionalized strong basic anion exchange resin was successfully synthesized and used for Cr(IV) extraction. This paper, reports on further synthesis and application of this resin for adsorption and separation of Re(VII) and Mo(VI), especially from copper arsenic filter cake. RESULTS: At pH 6.25, Re(VII) and Mo(VI) can be effectively separated with the N‐methylimidazolium functionalized strong basic anion exchange resin, giving a Re(VII) recovery of up to 93.3%, but only 5.1% for Mo(VI). When using the copper arsenic filter cake sample 89.1% Re(VII) recovery was achieved. CONCLUSION: The N‐methylimidazolium functionalized strong basic anion exchange resin exhibited high selectivity and recovery for Re(VII) in a mixed system. © 2012 Society of Chemical Industry 相似文献
996.
997.
Marisa Erencia Montserrat López‐Mesas Fernando Carrillo‐Navarrete 《Polymer International》2013,62(9):1316-1323
The thermosensitive properties of the hydrogel poly(N‐isopropylacrylamide) (pNIPAAm) together with the good mechanical properties of lyocell fibres make a combination of the two to be thought of as a smart textile. In the present study the optimal values of various parameters that control the grafting process of pNIPAAm onto lyocell fibres were determined considering the influence of the interaction between them. The copolymerization of pNIPAAm hydrogel onto lyocell fibres was performed in aqueous acidic medium using cerium(IV) as initiator. An experimental design was planned in order to study the effect of the interactions between some variables that affect the kinetics of the graft copolymerization: the cerium(IV) initiator concentration, the N‐isopropylacrylamide (NIPAAm) monomer concentration and the liquor fibre‐to‐bath ratio. The results show that the interaction between the concentrations of NIPAAm and the initiator significantly affects the degree of grafting (DG), the optimum values being 1250 and 12.25 mmol L?1, respectively. In contrast, the liquor ratio parameter shows no significant interaction with the other two variables studied, meaning that it acts independently but showing a proportional relationship with respect to the DG obtained. In addition, the presence of pNIPAAm in the copolymer obtained was confirmed by Fourier transform infrared spectral analysis. Moreover, the water sorption capacity, depending on the temperature, of the lyocell/pNIPAAm copolymer was studied, with an increase being observed when the DG is higher than 60% and also increasing with the temperature.© 2012 Society of Chemical Industry 相似文献
998.
Poly(N‐isopropylacrylamide‐co‐hydroxyethyl methacrylate) [P(NIPAM‐co‐HEMA)] copolymer was synthesized by controlled radical polymerization from respective N‐isopropylacrylamide (NIPAM) and hydroxyethyl methacrylate (HEMA) monomers with a predetermined ratio. To prepare the thermosensitive and biodegradable nanoparticles, new thermosensitive graft copolymer, poly(L ‐lactide)‐graft‐poly(N‐isoporylacrylamide‐co‐hydroxyethyl methacrylate) [PLLA‐g‐P(NIPAM‐co‐HEMA)], with the lower critical solution temperature (LCST) near the normal body temperature, was synthesized by ring opening polymerization of L ‐lactide in the presence of P(NIPAM‐co‐HEMA). The amphiphilic property of the graft copolymers was formed by the grafting of the PLLA hydrophobic chains onto the PNIPAM based hydrophilic backbone. Therefore, the graft copolymers can self‐assemble into uniformly spherical micelles ò about 150–240 nm in diameter as observed by the field emission scanning electron microscope and dynamic light scattering. Dexamethasone can be loaded into these nanostructures during dialysis with a relative high loading capacity and its in vitro release depends on temperature. Above the LCST, most of the drugs were released from the drug‐loaded micelles, whereas a large amount of drugs still remains in the micelles after 48 h below the LCST. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012 相似文献
999.
For the first time, acidic monomer chiral N‐acryloyl‐L ‐phenylalanine was polymerized directly by atom transfer radical polymerization under mild conditions. Controlled polymerization was carried out in pure water, methanol/water mixture, or pure methanol using water‐soluble initiators, such as 2‐hydroxyethyl‐2′‐methyl‐2′‐bromopropionate and sodium‐4‐(bromomethyl)benzoate at room temperature. The corresponding optically active biocompatible amino acid‐based homopolymers were obtained in good yields with narrow molecular weight distributions. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011 相似文献
1000.
Yewei Xu Xiangwang Cui Fanghua Zhu Xuan Luo Qiang Yin Lin Zhang 《Polymer International》2014,63(3):537-545
Six new bis(benzimidazolyl) monomers containing ether, sulfonyl and ketone groups were synthesized efficiently. A series of poly(N‐arylenebenzimidazole)s were prepared using an aromatic nucleophilic displacement reaction that removed the N–H sites from the novel bis(benzimidazolyl) derivatives with activated aromatic difluorides in sulfolane. The reaction was carried out at 210 °C in the presence of anhydrous potassium carbonate. All resulting polymers showed essentially amorphous patterns. This was consistent with the calculated results. Differential scanning calorimetry and thermogravimetric measurements showed that the polymers had high glass transition temperatures (>240 °C), good thermostability and high decomposition temperatures (>400 °C). These novel polymers also showed easy solubility. © 2013 Society of Chemical Industry 相似文献