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921.
James V. Crivello 《Journal of polymer science. Part A, Polymer chemistry》2009,47(21):5639-5651
Diaryliodonium salts undergo facile reduction by the dialkylborane, 9‐BBN. The combination of these two reagents constitutes a redox couple that can be employed as a convenient and versatile initiator system for the cationic polymerizations of styrenic monomers, vinyl ethers and the ring‐opening polymerizations of cyclic ethers and acetals including; epoxides, oxetanes, tetrahydrofuran, and 1,3,5‐trioxane. The polymerizations of these monomers can be carried out in either neat monomer or under solution conditions. Typically, the redox cationic polymerizations of the above monomers are rapid and exothermic. Optical pyrometry (infrared thermography) was employed as a convenient method with which to monitor and optimize the aforementioned redox initiated cationic polymerizations. Studies of the effects of variations in the structure and concentrations of the diaryliodonium salt and 9‐BBN on the polymerizations of various monomers were carried out. A mechanism for the redox cationic initiation of the polymerizations was proposed. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5639–5651, 2009 相似文献
922.
Fabao Zhao Zhilei Liu Liang Feng Jianping Sun Jiwen Hu 《Journal of Polymer Science.Polymer Physics》2009,47(14):1345-1355
Optically active poly(ethylene glycol) monomethyl ether‐b‐poly(methacryloyl‐L ‐leucine methyl ester) (denoted as MPEG‐b‐PMALM) copolymers were prepared via atom transfer radical polymerization (ATRP), using bromine (Br) end‐capped poly(ethylene glycol) monomethyl ether (denoted as MPEG‐Br) as macroinitiator in the presence of CuBr/tris(2‐dimethylaminoethy1)amine (Me6TREN) as catalytic system. Broad range of morphologies, such as spherical, cylindrical, and vesicular micelles, which were prepared by initially dissolving prepared polymer in organic solvent at different concentration followed by addition various amount of water before dialysis against water to remove any added solvent, was observed by transmission electron microscope (TEM). More detailed chiroptical properties of the micelles/aggregates in aqueous solution were evaluated by circular dichroism (CD) spectroscopy as a function of micelles morphologies, polymer concentration, solvents employed, temperature, etc. The micellar solutions exhibit almost the same CD spectra regardless of its morphologies. The intensity of the CD spectra of the cylindrical micelles decreased in the molar ellipticities as the micellar concentration in water was increased. The Cotton effect was markedly changed when the solvent hydrophobicity was changed by addition of trifluoromethyl ethanol (TFME) to water. The intensity of the CD spectra decreased not too much within the temperature range from 20 °C to 90 °C, indicating good stability of the micelles upon temperature variation. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 1345–1355, 2009 相似文献
923.
The effect of the hydrophobic properties of blocks B and C on the aggregate morphologies formed by ABC linear triblock copolymers in selective solvent was studied through the self‐consistent field theory. Five typical micelles, such as core‐shell‐corona, hamburger‐like, segmented‐wormlike, were obtained by changing the hydrophobic properties of blocks B and C. The simulation results indicate that the shape and size of micelle are basically controlled by the hydrophobic degree of the middle block B, whereas the type of micelle is mainly determined by the hydrophobic degree of the end block C. © 2009 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 484–492, 2009 相似文献
924.
Jinyao Liu Zhihua Nie Yong Gao Alex Adronov Huaming Li 《Journal of polymer science. Part A, Polymer chemistry》2008,46(21):7187-7199
Covalent functionalization of alkyne‐decorated multiwalled carbon nanotubes (MWNTs) with a well‐defined, azide‐derivatized, thermoresponsive diblock copolymer, poly(N,N‐dimethylacrylamide)‐poly(N‐isopropylacrylamide) (PDMA‐PNIPAM) was accomplished by the Cu(I)‐catalyzed [3 + 2] Huisgen cycloaddition. It was found that this reaction could simultaneously increase the molecular size and bonding density of grafted polymers when PDMA‐PNIPAM micelles were employed in the coupling system. On the other hand, attachment of molecularly dissolved unimers of high‐molecular weight onto the nanotube resulted in low‐graft density. The block copolymer bearing azide groups at the PDMA end was prepared by reversible addition–fragmentation transfer polymerization, which formed micelles with a diameter of ~40 nm at temperatures above its critical micelle temperature. Scanning electron microscopy was utilized to demonstrate that the coupling reaction was successfully carried out between copolymer micelles and alkyne‐bearing MWNTs. FTIR spectroscopy was utilized to follow the introduction and consumption of alkyne groups on the MWNTs. Thermogravimetric analysis indicated that the functionalized MWNTs consisted of about 45% polymer. Transmission electron microscopy was utilized to image polymer‐functionalized MWNTs, showing relatively uniform polymer coatings present on the surface of nanotubes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 7187–7199, 2008 相似文献
925.
YANG Zigang ZHOU Fen YUAN Jianjun MA Lixin ZHAI Chao & CHENG Shiyuan . School of Chemistry Materials Science Hubei University Wuhan China . School of Life Science Hubei University Wuhan China 《中国科学B辑(英文版)》2006,49(4):357-362
With the successful sequencing of Human Genome, it would be possible to cure all diseases by gene ther- apy in the near future. However, one of the major problems in gene therapy is the development of gene vectors. To date, there are two kinds of gene vectors, namely, viral and non-viral gene vectors. Viruses are widely used as vectors in gene therapy, with the trans- fection efficiency being relatively high, but they have the safety problems such as immunogenicity, non- biocompatibility and … 相似文献
926.
Guiying Li Sen Song Lei Guo Songmei Ma 《Journal of polymer science. Part A, Polymer chemistry》2008,46(15):5028-5035
Self‐assembled thermo‐ and pH‐responsive poly(acrylic acid)‐b‐poly(N‐isopropylacrylamide) (PAA‐b‐PNIPAM) micelles for entrapment and release of doxorubicin (DOX) was described. Block copolymer PAA‐b‐PNIPAM associated into core‐shell micelles in aqueous solution with collapsed PNIPAM block or protonated PAA block as the core on changing temperature or pH. Complexation of DOX with PAA‐b‐PNIPAM triggered by the electrostatic interaction and release of DOX from the complexes due to the changing of pH or temperature were studied. Complex micelles incorporated with DOX exhibited pH‐responsive and thermoresponsive drug release profile. The release of DOX from micelles was suppressed at pH 7.2 and accelerated at pH 4.0 due to the protonation of carboxyl groups. Furthermore, the cumulative release of DOX from complex micelles was enhanced around LCST ascribed to the structure deformation of the micelles. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 5028–5035, 2008 相似文献
927.
Yali Luo Xinjian Yao Jinfang Yuan Tao Ding Qingyu Gao 《Colloids and surfaces. B, Biointerfaces》2009,68(2):218-224
Block copolymers, poly(N-vinylprrolidone)-block-poly(styrene-alter-maleic anhydride) (PVP-b-PSMA) and poly(N-vinylprrolidone)-block-poly(N,N-dimethylaminoethyl methacrylate) (PVP-b-PDMAEMA), were synthesized by reversible addition- fragmentation chain transfer (RAFT) polymerization. In aqueous media, this a pair of oppositely-charged diblock copolymers could self-assemble into stable and narrow distribution polyion complex micelles (PICMs). Transmission electron micrographs (TEM) and dynamic light scattering (DLS) analysis showed that the micelles to be spherically shaped with mean hydrodynamic diameter around 70 nm. In addition, the PICMs display ability to response to external stimuli. All of theses features are quite feasible for utilizing it as a novel intelligent drug delivery system. In order to assess its application in biomedical area, release profiles of coenzyme A (Co A) from PICMs were studied under both simulated gastric and intestinal pH conditions. The release was much quicker in pH 7.4 buffer than in pH 2.0 solution. Based on these results, these PICMs could be a potential pH-sensitive carrier for colon-specific drug delivery system. 相似文献
928.
929.
930.
The stretched exponential photoluminescence decay of the energy-resolved broadband emission of purified and unpurified CdS quantum dots (QDs) made in reverse micelles is characterized as a function of photolysis time and thiol addition. Photolysis is found to proportionately increase both the lifetime and quantum yield of these QDs. This proportionality is consistent with a simple parallel channel model of the decay of the excited states. The ultimate QY of the purified sample is found to be as high as 24%, which is twice that previously reported for this preparation. At −70 °C both the QY and the lifetime increase by more than a factor of two, indicating that thermal quenching limits the QY at room temperature. Finally, the addition of alkanethiols is shown to red-shift and quench the emission while only modestly altering the lifetime. These thiolated QDs show an extremely large temperature dependence of QY, demonstrating stronger thermal quenching than the unfunctionalized QDs. 相似文献