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61.
Daoben Hua Xueping Ge Jing Tang Xiulin Zhu Ruke Bai Caiyuan Pan 《Journal of polymer science. Part A, Polymer chemistry》2007,45(14):2847-2854
The free‐radical polymerization of methyl acrylate (MA) has been studied in the presence of a novel cyclic dixanthate under γ‐ray irradiation (80 Gy min?1) at room temperature (~28 °C), ?30 °C, and ?76 °C respectively. The resultant polymers have controlled molecular weights and relatively narrow molecular weight distributions, especially at low temperatures (i.e., ?30 and ?76 °C). The polymerization control may be associated with the temperature: the lower the temperature is, the more control there is. Matrix‐assisted laser desorption/ionization time‐of‐flight mass spectrometry analysis of poly(methyl acrylate) (PMA) samples shows that there are at least three distributions: [3‐(MA)n‐H]+ cyclic polymers, [3‐(MA)n‐THF‐H]+, and [3‐(MA)n‐(THF)2‐H]+ linear PMAs. The relative content of the cyclic polymers markedly increases at a lower temperature, and this may be related to the reduced diffusion rate and the suppressed chain‐transfer reaction at the low temperature. It is evidenced that the good control of the polymerization at the low temperature may be associated with the suppressed chain‐transfer reaction, unlike reversible addition–fragmentation chain transfer polymerization. In addition, styrene bulk polymerizations have been performed, and gel permeation chromatography traces show that there is only one cyclic dixanthate moiety in the polymer chain. This article is the first to report the influence of a low temperature on controlled free‐radical polymerizations. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 2847–2854, 2007 相似文献
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63.
Xueping Liu Ji‐Qiang Chen Minghui Zhang Ying Wu Miao Yang Ke Zhang 《Journal of polymer science. Part A, Polymer chemistry》2019,57(17):1811-1820
A versatile method was introduced to prepare cyclic polymers from both conjugated and unconjugated vinyl monomers. It was developed on the combination of the RAFT polymerization and the self‐accelerating double strain‐promoted azide‐alkyne click (DSPAAC) reaction. In this approach, a switchable chain transfer agent 1 was designed to have hydroxyl terminals and a functional pyridinyl group. The protonation and deprotonation of pyridinyl group endowed the chain transfer agent 1 with a switchable control capability to RAFT polymerization of both conjugated and unconjugated vinyl monomers. Based on this, RAFT polymerization and the following hydroxyl end group modification were used to prepare various azide‐terminated linear polymers including polystyrene, poly(N‐vinylcarbazole), and polystyrene‐block‐poly(N‐vinylcarbazole). Using sym‐dibenzo‐1,5‐cyclooctadiene‐3,7‐diyne (DBA) as small linkers, the corresponding cyclic polymers were then prepared via the DSPAAC reaction between DBA and azide terminals of the linear precursors. Due to the self‐accelerating property of DSPAAC reaction, this bimolecular ring‐closing reaction could efficiently produce the pure cyclic polymers using excess molar amounts of DBA to linear polymer precursors. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1811–1820 相似文献
64.
Organosilicon compounds play an important role in the fields of materials science,pharmacy,and organic synthesis.The development of effective approaches for the preparation of these compounds have also become a research focus in organic synthesis.In recent years,free radical synthesis of organosilicons has been vigorously developed,which generally has the advantages of milder synthesis conditions,higher yields and selectivity,and free of precious metal catalysts compared with traditional strategies.This article reviews research progresses in the synthesis of organosilico n compounds by free radical pathways since 2016.In most cases,the radical silylation is achieved based on the reaction of silyl radicals,which are triggered by four routes including peroxide,transition-metal-induced peroxide decomposition,alkali,photocatalysis.The alkyl radicals can also initiate the radical silylation for the generation of C(sp~3)—Si bonds. 相似文献
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66.
Molecular technique with STRs can rapidly diagnose aneuploidy. In order to improve its fidelity, we developed a novel STR-based strategy for fast diagnosis of trisomy 21 and constructed a multimarker diagnostic system according to it. The system is based on nine STRs, of which two were previously known and seven were newly identified from the genomic sequence of the long arm of chromosome 21. They were confirmed to be highly polymorphic in the Chinese population by PCR amplification and gel electrophoresis. The combination of nine STR markers, when applied to DNA from 102 Chinese individuals with normal karyotype, did not yield any false-positives, and clearly revealed three different alleles in DNA from 15 out of 18 trisomy 21 patients. The results show that our new strategy can provide an alternative molecular technique for the rapid detection of aneuploidy. 相似文献
67.
Controlled radical polymerization of MA has been achieved in the presence of a cyclic trithiocarbonate, 1,5-dihydro-2,4-benzodiehiepine-3-thione, under γ-ray irradiation (60 Gy/min) at low temperature. The narrow molecular weight distributions and the linear kinetics curve indicate that the polymerization is a controlled free-radical process at low temperature (especially at −76 °C). The structures of resultant polymers were characterized by matrix assisted laser desorption/ionization time-of-flight mass spectrometry, and the results show that cyclic polymers can be formed at −76 °C, which may result from the reduced diffusion rate and the suppressed chain-transfer reaction at the lower temperature. It is further evidenced that the good control of the polymerization at the lower temperature may be associated with the suppressed chain-transfer reaction, not like reversible addition-fragmentation transfer polymerization. The linear polymers probably result from the polymer chain radicals reacting with the radicals produced by the interaction of the irradiation and the monomer. 相似文献
68.
A method has been developed for the determination of copper and zinc in the serum of rats by derivative microsampling flame atomic absorption spectrometry (D-MFAAS). The microsampling volume, solution uptake rate and other figures of merit of the proposed methodology were studied. For a 100 microl volume, the characteristic concentrations and detection limits (3s) of D-MFAAS were 0.023 and 0.013 microg ml(-1) for copper and 0.0066 and 0.0080 microg ml(-1) for zinc, which were 4.5-6.5-fold better than those of microsampling flame atomic absorption spectrometry (MFAAS). The detection limits and sensitivities of D-MFAAS were 6.4- and 16-fold for 300 microl volume for copper, 14- and 13-fold for 250 microl volume for zinc, better than those of MFAAS. The method demonstrates high tolerance to interferences, and the analytical results obtained for a certified reference material, GBW 08551 Pork Liver, were in good agreement with the certified values. The recovery with the standard additions method was good, in the range 97.6-101.5%, and precisions (relative standard deviations) obtained for a diluent sample containing 0.5 microg ml(-1) copper and 0.7 microg ml(-1) zinc were 4.0% and 3.5% (n = 15) for copper and zinc, respectively. 相似文献
69.
Lei?LinEmail author Yujie?Liu Chulchae?Choi Xueping?Zhang Ray?T.?Chen 《Optical Review》2003,10(2):124-127
We report here a demonstration of hybrid integration of a 1 × 12 metal-semiconductor-metal (MSM) photodetector array and polyimide channel waveguides via 45° total-internal-reflection (TIR) micro-couplers. The two-layer polyimide waveguide array was constructed using Ultradel 9120D for the core and Ultradel 9020 for the lower cladding layer. The coupling loss and propagation loss of the waveguide are 0.2dB and 0.21 dB/cm, respectively. The cross talk of the adjacent channels is -32 dB. The MSM photodetector array was fabricated on a semi-insulated GaAs wafer. The photodetectors are integrated to operate in the conventional vertical illumination mode. We measured the external quantum-efficiency and 3 dB bandwidth of the integrated MSM photodetectors at 0.4 A/W and 2.648 GHz, respectively. The aggregate 3 dB bandwidth of the 12-channel integrated system is 32 GHz. 相似文献
70.
Zhu H Gao X Lan Y Song D Xi Y Zhao J 《Journal of the American Chemical Society》2004,126(27):8380-8381
Hydrogen titanate nanofibers synthesized by a hydrothermal reaction, are chemically reactive, readily reacting with dilute acid. This reaction is a topochemical process in which in situ phase transition from H-titanate to anatase takes place and the product retains the fibril morphology. The extent of this reaction can be precisely controlled, allowing us to achieve a delicate composite structure at nanoscale: long titanate fibers of 40-100 nm thick and up to 30 mum long covered with anatase nanocrystals of 10-30 nm. The structure has desired photocatalytic properties and can be separated readily after use. This study demonstrates new opportunities to create delicate inorganic nanostructures with advanced functions by wet chemical reactions. 相似文献