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Ananthalakshmi N. R Wadgaonkar P. P Sivaram S. Varma I. K. 《Journal of Thermal Analysis and Calorimetry》1999,58(3):533-539
The paper describes the effect of molecular mass and copolymer composition on thermal behaviour of homopolymers and copolymers of glycidyl methacrylate and methyl methacrylate. The polymerisation was done by using group transfer polymerization (GTP) and free radical techniques. A multistep decomposition was observed in polymers prepared by free radical technique indicating the presence of weak linkages in the backbone. Copolymers prepared by GTP had fewer weak sites and degraded in single step by a random chain scission.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
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Kathy C. Chuang Daniel A. Scheiman Joyce Fu Marcus Crawford 《Journal of polymer science. Part A, Polymer chemistry》1999,37(14):2559-2567
Thermoplastic and thermoset polyimides derived from 2,2-bis[4-(4-aminophenoxy)phenyl]propane (BAPP) and 4,4′-bis(4-aminophenoxy)-2,2′-dimethylbiphenyl (BAPD) were prepared and characterized. Their physical and thermal properties as well as the polyelectrolyte effect exhibited by BTDA–BAPP polyamic acids in NMP solution were discussed. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 2559–2567, 1999 相似文献
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Peter Politzer Jane S. Murray Pat Lane 《International journal of quantum chemistry》2009,109(3):534-539
For five prototypical energetic molecules (nitrobenzene, methyl azide, methyl nitrate, nitromethane, and dimethylnitramine), we examine computationally the effects of external electric fields upon their “trigger linkage” bonds, the breaking of which is believed to play a key role in detonation initiation. The bonds are, respectively, C? NO2, N? N2, O? NO2, C? NO2, and N? NO2. The calculations are at the B3PW91/6–31G** level. We find that fields along these bonds that reinforce the molecules' intrinsic polarities also lower their energies and increase the bonds' stretching vibration frequencies. This suggests a strengthening of the bonds. Fields in the opposite direction do the reverse. © 2008 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 相似文献
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In this paper, the three-dimensional Fourier series which can describe the coupler curves of spatial linkages are derived. Based on the geometric properties of one-dimensional and two-dimensional Fourier series, a geometric constraint conditions are proposed to establish the three-dimensional Fourier series. The geometric meaning of mechanism for the three-dimensional Fourier series is put forward. Finally, an example is given to show the feasibility and the validity of this approach. 相似文献
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Prithankar Pramanik Debdatta Halder Siddhartha Sankar Jana Suhrit Ghosh 《Macromolecular rapid communications》2016,37(18):1499-1506
The synthesis, micellar aggregation, and pH‐triggered intracellular drug delivery ability of an amphiphilic statistical copolymer (P2) are studied. Two methacrylate derivatives, one containing a hydrophilic pendant and the other containing a hydrophobic pendant chain, are copolymerized to produce P2. The hydrophobic pendant chain is linked to the polymer backbone by a β‐thiopropionate linkage, known to undergo slow hydrolysis at mild acidic pH. P2 forms a multimicellar cluster in water with a critical aggregation concentration of 0.02 mg mL−1 and encapsulates a hydrophobic guest such as pyrene, Nile red, or the anti‐cancer drug doxorubicin (Dox). Sustained release of the entrapped Dox (80% after 100 h) is noticed at pH 5.2, while release is significantly slower (35% after 100 h) at pH 7.4. Acidic hydrolysis of the β‐thiopropionate linkage leading to the reduction of the hydrophobicity is established as the cause for micellar disassembly and triggered drug release. Cell‐culture studies with the human breast cancer cell line, MCF‐7, reveal biocompatibility of P2 (below 150 μg mL−1). It is further tested for intracellular delivery of Dox. MCF‐7 cells remain healthy at pH 7.4 but become unhealthy at pH 5.2 when treated with a Dox‐loaded P2 micelles.
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《中国化学快报》2020,31(5):1301-1304
Palladium-catalyzed highly meta-selective CH iodination of phenylacetic acid, benzylphosphonate and benzylsulfonate scaffolds with molecular I2 is developed using a pyridine-type template. The practical ester linkages enable the directing template easily installed and readily removed. The substrate scope is broad, and alkyl, methoxyl, trifluomethyl, and halo substituents are compatible with this reaction. Further transformations of ibuprofen iodide intermediates by Pd-catalyzed CC and C–heteroatom bond formation illustrate the broad utility of this method. 相似文献
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The LC/UV-DAD/ESI-MSn negative fragmentation mode of 23 O-glycosylated flavonoids with two, three, four and five hexoses was studied. The results show that it is possible to differentiate the (1-->2) and (1-->6) interglucosidic linkages and also to discern between the flavonoid isomers with two glucoses (sophorosides, gentiobiosides and X,Y-diglucosides), three glucoses (sophorotriosides and X-sophoroside-Y-glucoside) and four glucoses (X-sophorotriosides-Y-glucoside and X-sophoroside-Y-sophoroside). In the characterization of the (1-->2) and (1-->6) interglycosidic linkages, the Y1- (-162 u) and Z1- (-180 u) ions play a relevant role. In the first case ions with high relative abundance (13-79%) are found, whereas in the other cases they are in very low abundance or absent. X,Y-di-O-glucoside flavonoids can be differentiated from the O-diglucoside flavonoids by the presence of Y1- (base peak) and Y0- (approximately 30%) ions and the absence of Z1- ions. Regarding flavonoids glycosylated with three glucoses, X-sophoroside-Y-glucoside flavonoids show the Y7(0-) (-162 u) ion as the only peak in MS2 events whereas in sophorotrioside flavonoids various ions due to intermediate fragmentations are observed. These ions are characteristic of a (1-->2) interglucosidic linkage. In MS2 experiments on flavonoids with four glucoses (X-sophorotrioside-Y-glucoside and X-sophoroside-Y-sophoroside), the base peak indicated the total loss of the sugar moieties in position 7. In addition, the characterization of the type of interglycosidic linkage in flavonoids glycosylated with five sugars can be achieved. On the other hand, in tetra- and pentaglycosylated flavonoids, the ions that characterize the (1-->2) interglucosidic linkage formed by intermediate fragmentation of the oligosacharide residues (sophorosides and sophorotriosides) are found in much higher relative abundance in MS3 than in MS2 experiments, where they are almost not detected. 相似文献
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A graph is k-linked if for every set of 2k distinct vertices {s1,…,sk,t1,…,tk} there exist disjoint paths P1,…,Pk such that the endpoints of Pi are si and ti. We prove every 6-connected graph on n vertices with 5n−14 edges is 3-linked. This is optimal, in that there exist 6-connected graphs on n vertices with 5n−15 edges that are not 3-linked for arbitrarily large values of n. 相似文献