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Two-component thermo-responsive hydrogels poly(N-isopropylacrylamide)-co-vinylbenzyltrimethylammonium chloride (NIPA-co-VBT) and poly(N-isopropylacrylamide)-co-p-sodium styrene sulphonate (NIPA-co-SSS) were prepared by using high energy gamma radiation. The gels were characterized by Fourier transformed infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and sol-gel analysis. The presence of ionic monomers in NIPA leads to lower gel content. Introduction of ionic components in the matrix enhanced swelling extent but caused slower volume transition. The swelling studies in alcohol indicated that swelling extent was function of polarity of the swelling medium and all gels followed the order water > methanol > ethanol > iso-propanol. In mixed co-solvents (water-alcohol), they exhibit complex reentrant behavior. The co-polymer gels containing VBT swelled faster and to higher extent than those containing SSS. The dynamic swelling studies indicated that diffusion of water in PNIPA gel shifts from Fickian for PNIPA to anomalous for NIPA-co-ionic gels also the mean swelling time (MST) decreases for gels containing ionic monomers. 相似文献
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Alexopoulos T Allen C Anderson EW Areti H Banerjee S Beery PD Biswas NN Bujak A Carmony DD Carter T Cole P Choi Y De Bonte RJ Erwin AR Findeisen C Goshaw AT Gutay LJ Hirsch AS Hojvat C Kenney VP Lindsey CS LoSecco JM McMahon T McManus AP Morgan N Nelson KS Oh SH Piekarz J Porile NT Reeves D Scharenberg RP Stampke SR Stringfellow BC Thompson MA Turkot F Walker WD Wang CH Wesson DK 《Physical review letters》1990,64(9):991-994
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Lazarus EA Navratil GA Greenfield CM Strait EJ Austin ME Burrell KH Casper TA Baker DR DeBoo JC Doyle EJ Durst R Ferron JR Forest CB Gohil P Groebner RJ Heidbrink WW Hong R Houlberg WA Howald AW Hsieh C Hyatt AW Jackson GL Kim J Lao LL Lasnier CJ Leonard AW Lohr J La Haye RJ Maingi R Miller RL Murakami M Osborne TH Perkins LJ Petty CC Rettig CL Rhodes TL Rice BW Sabbagh SA Schissel DP Scoville JT Snider RT Staebler GM Stallard BW Stambaugh RD St John HE Stockdale RE Taylor PL Thomas DM 《Physical review letters》1996,77(13):2714-2717
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Anjali Acharya A. Goswami P. K. Pujari S. Sabharwal S. B. Manohar 《Journal of polymer science. Part A, Polymer chemistry》2002,40(8):1028-1036
Positron annihilation lifetime spectroscopy was used to characterize the reentrant volume‐phase‐transition behavior of poly(N‐isopropyl acrylamide) hydrogel in an ethanol/water mixed solvent. The polymer gel was synthesized with γ irradiation. The ortho‐positronium lifetime (τ3) in the gel slowly increased with an increase in the ethanol content in the mixed solvent. τ3 was not influenced by the volume phase transition. The ortho‐positronium intensity decreased with the collapse of the gel in an approximately 10% ethanol/water mixture. When swelled in pure ethanol, τ3 initially increased with the solvent amount in the gel, showing the destruction of intramolecular hydrogen bonding and the relaxation of polymer chains. The lower critical solution temperature of the gel in the 10% ethanol/water mixture was lower than that in pure water, and τ3 for various solvent contents showed behavior similar to that seen in pure solvent. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1028–1036, 2002 相似文献
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Thermogravimetric analysis (TGA) and differential scanning calorimetric (DSC) studies were carried out on gamma radiation synthesized polydiallyldimethylammonium chloride (PDADMAC). The polymer was found to undergo thermal degradation in two stages. The first stage showed a weight loss of 33% and the second stage showed a weight loss of 67%. The DSC thermogram shows two endothermic peaks corresponding to the two stages in the TG thermogram and the experimental enthalpy change associated with the first and second stages were 650 J g−1 and 129.5 J g−1, respectively. The nth-order kinetic parameters (order of the reaction, activation energy and the pre-exponential factor) were determined from a single dynamic DSC or thermogravimetric (TG) thermogram by the method of least square. Theoretical TG/differential thermogravimetric (DTG) and DSC thermograms derived from the calculated kinetic parameters were in good agreement with the experimental ones at the heating rate employed. However, the kinetic parameters determined using TG and DSC were different. This leads to the conclusion that the degradation mechanism could be complicated and may consists of a number of parallel or consecutive reactions. The glass transition temperature (Tg) of the polymer was found to be around 150 °C depending on the test method employed. 相似文献
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C. V. Chaudhari K. A. Dubey Y. K. Bhardwaj S. Sabharwal 《Journal of Macromolecular Science: Physics》2013,52(5):839-859
Different compositions of SBR/EPDM 50:50 blends containing multiple-walled carbon nanotubes (MWNT) as nanoparticulate fillers (0.5%–10%) were evaluated for radiation sensitivity and solvent permeability. The efficiency of radiation ***cross-linking was analyzed by gel-content and Charlesby–Pinner parameter measurements. ***Gamma-radiation-induced cross-linking extent was found to increase with radiation dose and MWNT concentration, which was reflected in different extents of swelling. Rigorous analysis of swelling and diffusion data, on the basis of the transport exponent (n) values and diffusion/relaxation rate indicated anomalous diffusion behavior for most of the nanocomposites. The swelling extent in different solvents was found to be a function of polymer-solvent interaction as well as stearic hindrance due to the structure/size of the solvent molecules. Polymer-filler interaction investigated by a Kraus plot indicated high reinforcement of the SBR/EPDM matrix on MWNT addition. There was no significant change in surface energy or hydrophilicity of the SBR/EPDM matrix on introduction of MWNT into it. 相似文献
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The starting material for any crystal growth contains a number of impurities. The level of an impurity affecting a particular property of the crystal varies from one impurity to another. We report here the effect of some select impurities usually present in NaI material on its growth and scintillation response. 相似文献
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Dhavale DD Kumar KS Chaudhari VD Sharma T Sabharwal SG Prakashareddy J 《Organic & biomolecular chemistry》2005,3(20):3720-3726
The D-glucose derived aziridine carboxylate 5 was obtained from (E)-ethyl-6-bromo-1,2-O-isopropylidene-3-O-benzyl-5-deoxy-alpha-D-xylo-5-eno-heptofuranuronate 4 through conjugate addition of benzylamine and in situ intramolecular nucleophilic expulsion of bromine. The regioselective aziridine ring-opening, using water as a nucleophile, resulted in the alpha-hydroxy-beta-aminoester 6, which was exploited in the synthesis of six and five membered azasugars 1b/1c and 2b/2c, respectively. The glycosidase inhibitory activity of the title compounds was evaluated. 相似文献