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1.
Phase transitions of poly(N-isopropylacrylamide-co-acrylic acid) (PiPA-AA) and poly(N,N- diethylacrylamide-co-acrylic acid) (PdEA-AA) in water have been investigated by means of turbidimetry, Fourier transform infrared (FTIR) spectroscopy and differential scanning calorimetry (DSC). The phase transition temperatures (Tp) of these copolymers increase with the degree of ionization () of the acrylic acid (AA) units, which in turn is dependent on the pH of the solutions. Apparent values of pKa for the AA units, determined from the pH dependencies of Tp, are 4.7 and 5.4 for PiPA-AA and PdEA-AA, respectively. Differences between Tp for PiPA-AA and Tp for PiPA homopolymer (Tp) are +1.5 and –0.2 °C/mol% of AA at =1 and 0, respectively. The values of Tp for PdEA-AA are +2.6 (ionic) and –0.5 (nonionic)°C/mol%, indicating that the incorporated AA units have a larger effect on PdEA than on PiPA. DSC measurements performed with each of these copolymers at different pH values show a linear relationship between Tp and the enthalpy of transition (H). IR measurements of PiPA-AA show that the profiles of IR bands from both iPA and AA units exhibit critical changes at Tp of the copolymer. Heating the solution above Tp leads to shifts of the amide II, C–H stretch, and C–H bend bands from the iPA units toward lower wavenumbers, as well as a shift of the amide I band from the iPA units toward higher wavenumbers. A decrease in the intensity of the symmetric C=O stretch IR band from carboxylate anions (1560 cm–1), and an increase in the intensity of the C=O stretch band from COOH groups (1705 cm–1) suggest that a partial protonation of the carboxylate groups (COO–+H+COOH) takes place upon the phase transition. 相似文献
2.
Amphiphilic diblock copolymers consisting of 2-(N, N-dimethylamino)ethyl methacrylate (DMAEMA, abbreviated as DMA) and stearyl methacrylate (SMA) with different degrees of polymerization
and compositions were prepared by reversible addition–fragmentation chain transfer (RAFT) copolymerization. The composition
and chemical structures of (co)polymers were confirmed by the measurements of 1H NMR spectroscopy and gel permeation chromatography (GPC). The self-aggregating structures of amphiphilic diblock copolymers
with the concentration of 0.1~0.3 wt.% in THF/water mixed solvent was investigated by transmission electron microscopy (TEM)
and dynamic light scattering (DLS). It was found that both the morphologies and aggregating particle size resulted from the
amphiphilic diblock copolymers depended on the variation of pH values, the lengths of the hydrophobic PSMA chains, and the
weight ratio of THF/water mixed solvent. 相似文献
3.
Li-qin Cao Liu-ping Chen Ji-qing Jiao Shu-ying Zhang Wei Gao 《Colloid and polymer science》2007,285(11):1229-1236
Herein, we report a new method that has been developed to prepare thermoresponsive polymers. The white, dry, fine powders
were obtained directly from cross-linking polymerization of N-isopropylacrylamide in supercritical carbon dioxide (scCO2) with N,N-methylenebisacrylamide as a cross-linker. The effects of the reaction pressure and time as well as the initial concentrations
of the initiator, cross-linker, and monomer on the yield and morphology of the resulting polymer were investigated systematically.
The polymer yield was increased with the concentrations of the cross-linker, monomer, and reaction time. Under the condition
of using higher cross-linker concentrations, the cross-linked poly (N-isopropylacrylamide) microparticles with diameters of 50 nm were generated in scCO2 in high-yield and short reaction times. These results suggest that the synthetic method using scCO2 can be used to prepare biomedical materials such as the controlled drug-release system. 相似文献
4.
The structural transition of the l- and dl forms of poly(N-(1- hydroxymethyl)propylmethacrylamide (PHMPMA) in aqueous solution was studied by measuring the pressure dependence of the apparent scattering intensity, differential scanning calorimetry (DSC), and circular dichroism (CD). The thermodynamic implications of the results are discussed in relation to the chiral structure of the side chain, and differences in the thermal and barometric transitions. T-P diagrams of the transition showed characteristic ellipsoid features. Antagonism of the temperature and pressure effects was observed only for P(dl-HMPMA). For P(l-HMPMA), the transition temperature (T
tr) decreased with increasing pressure, and the highest T
tr was observed at atmospheric pressure (0.1 MPa). For both polymers, the highest P
trs were observed at the lowest temperatures. The l polymer showed a specific negative peak in its CD spectrum at around 220 nm in the lower temperature region and the temperature dependence was reproduced by a single-step transition, with the midpoint corresponding to the T
tr obtained from the scattering measurements. Coupled with the results from the DSC, the different behavior between the P(l-HMPMA) and P(dl-HMPMA) could be explained in terms of the chain states before and after the transition. The cooperative factors derived from the DSC measurement revealed that about 4 to 5 polymers of the present size were necessary to perform a thermal transition for P(l-HMPMA), and that P(dl-HMPMA) underwent its transition as an almost single molecular event.This revised version was published online in June 2005 with correction to the article category. 相似文献
5.
R. I. Kublashvili M. O. Labartkava K. P. Giorgadze D. Sh. Ugrekhelidze 《Chemistry of Natural Compounds》2008,44(4):413-415
N-Tolylglycosylamines were synthesized from o-, m-, and p-toluidines and aldoses (D-glucose, D-galactose, D-mannose, L-rhamnose, D-xylose, and L-arabinose). The anomeric and isomeric
compositions of the synthesized products were established using 13C NMR methods.
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Translated from Khimiya Prirodnykh Soedinenii, No. 4, pp. 333–335, July–August, 2008. 相似文献
6.
《European Polymer Journal》2002,38(7):1343-1347
In this study, hydrogels of poly(N-isopropylacrylamide-co-acrylamide) having a thermoresponsive character were prepared by a redox polymerization method. NIPAM-co-AAm hydrogels with different thermoresponsive properties were obtained by changing the initial NIPAM/AAm mole ratio and crosslinker concentration.Equilibrium-swelling ratio, dynamic swelling ratio and dynamic deswelling ratio were evaluated for all hydrogel systems. The fast shrinking was observed with all gels. The time required for equilibrium shrinking increased with the increase of acrylamide content in the gel. 相似文献
7.
Poly(vinyl alcohol), PVA, with different molecular weights, Mw, and degrees of hydrolysis has been used to study the steric stabilization of microgels based on poly(N-vinylcaprolactam). The stabilizer influences the particle size and stability, but has no influence on the thermal properties. The thermal behavior of microgels depends on the heating rate: slow heating leads to the formation of aggregates and fast heating to an intramolecular collapse. The aggregates showed an unusual angular dependence of the diffusion coefficient, which can be explained by the presence of probably an additional rotational diffusion. 相似文献
8.
I. M. Aladzheva O. V. Bykhovskaya P. V. Petrovskii T. A. Mastryukova 《Russian Chemical Bulletin》2007,56(12):2456-2459
Two methods for the synthesis of N-(2-chloroethyl)glycine and-DL-alanine esters are proposed: 1) reductive amination of the C=O group of glyoxilic or pyruvic acids upon treatment with 2-chloroethylamine
and sodium cyanoborohydride in methanol and 2) alkylation of 2-chloroethylamine with α-haloalkanoic acid esters in K2CO3-MeCN two-phase system.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2372–2374, December, 2007. 相似文献
9.
Electrochemical measurements including cyclic voltammetry, differential capacity, and chronocoulometry have been used to characterize the adsorption behaviors of the zwitterionic surfactant
N-dodecyl-N,N-dimethyl-3-ammonio-1-propanesulfonate (DDAPS) on the Au(111) electrode surface. The thermodynamics of the ideally polarized electrode have been employed to determine the Gibbs excess and the Gibbs energy of adsorption. The results show that the adsorption of DDAPS has a multistate character. The first two states are observed at potentials close to zero charge. At low bulk DDAPS concentrations, it corresponds to the formation of a film of nearly flat adsorbed molecules. At higher concentrations it is converted into a hemimicellar state. The second state is formed at negative potentials and charge densities close to 0 C cm–2. It corresponds to a film of tilted molecules oriented with the hydrocarbon tail towards the metal and the polar head toward the solution.Dedicated to Professor Zbigniew Galus on the occasion of his 70th birthday and in recognition of his many contributions to electrochemistry. 相似文献
10.
The properties of thermoresponsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogel in tetrahydrofuran/H2O mixtures were studied. Scanning electron microscopic (SEM) images demonstrate that the hydrogel changes from homogeneous to heterogeneous microstructure upon the addition of tetrahydrofuran to water. This heterogeneous PNIPAAm hydrogel in the mixture solvent exhibits a very slow response rate at temperatures above its lower critical solution temperature. The decreased response rate is attributed to the formation of special ternary complexes including the polymer and the two solvents in the tetrahydrofuran/H2O mixture. Factors controlling the thermoresponse rate are discussed further and several suggestions are provided for designing and developing fast-response PNIPAAm hydrogels in the future. 相似文献
11.
Dupard-Julien CL Kandlakunta B Uppu RM 《Analytical and bioanalytical chemistry》2007,387(3):1027-1032
A reversed-phase, high-performance liquid chromatography (RP-HPLC) method that allows quantitation of low levels of epoxides
has been described. The method involved derivatization of epoxides using 100- to 1,000-fold excess N,N-diethyldithiocarbamate (DTC) at 60 °C for 20 min at neutral pH. The unreacted DTC was then decomposed to CS2 and diethyl amine by acidification of the reaction mixture to pH 2 using orthophosphoric acid. The first two steps could
be performed in the same reaction vessel by sequential addition of reagents. In the final step, an aliquot (20 μL) of the
derivatized sample was analyzed for the presence of stable esters of DTC by RP-HPLC using a Supelcosil LC-18-S (150 × 4.6-mm)
column and a mobile phase consisting of 40% (v/v) acetonitrile in water at a flow of 1 mL min−1. Using UV detection at 278 nm, the epoxides gave linear responses in the concentration range of 0.25 to 50 μM. The method
is robust, and as low as 5 pmol of the analyte could be successfully detected and quantified with recoveries of ≥94%. Following
a minimal pretreatment such as ultrafiltration (molecular weight cutoff 5,000 Da), the method is suitable for analysis of
epoxides in complex physiological fluids (e.g., fetal bovine serum). The method has been rigorously evaluated and adapted
in our laboratory for routine analysis and determination of stability of epoxides of 1,3-butadiene and other alkenes added
to cell cultures. 相似文献
12.
Lignocellulose copolymers with grafted lactam rings were prepared by graft copolymerization of wood with N-vinylpyrrolidone initiated by Fe2+-H2O2. The principal features of their formation were investigated as functions of reactant concentrations, temperature, and polymerization
time.
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Translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 174–176, March–April, 2008. 相似文献
13.
V. E. Romanov E. E. Shul’ts M. M. Shakirov G. A. Tolstikov 《Chemistry of Natural Compounds》2008,44(3):346-351
New N-acylates of the norditerpenoid alkaloid N-deacetyllappaconitine that were modified in the aromatic ring and are interesting as potential pharmacologically valuable
compounds were prepared.
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Translated from Khimiya Prirodnykh Soedinenii, No. 3, pp. 275–279, May–June, 2008. 相似文献
14.
Kershaw JA Nekrassova O Banks CE Lawrence NS Compton RG 《Analytical and bioanalytical chemistry》2004,379(4):707-713
The effect of Cu(II) on the determination of homocysteine via its electrochemically initiated reaction with N,N-diethyl-p-phenylenediamine is examined. The presence of copper inhibited the detection process for homocysteine owing to a complexation reaction occurring. This provided an indirect route for the sensitive and selective determination of Cu(II), which produced a linear response over the range from 2.5 to 500 M and a limit of detection of 2.5 M. The detection pathway was examined in the presence of metallic and inorganic ions, with negligible interference observed. 相似文献
15.
Aytaç Gürhan Gökçe Hayati Türkmen Muhittin Aygün Bekir Çetinkaya Orhan Büyükgüngör 《Structural chemistry》2008,19(1):57-62
Trans-Bis[1,3-bis(2,4-dimethylphenylimidazolidin-2-ylidene)]dichloropalladium(II), 4, was prepared from 1,3-bis(2,4-dimetilphenyl)imidazoliniumchloride. The crystal and molecular structure of 4 have been determined by single crystal X-ray diffraction. The title compound, C38H44N4PdCl2, crystalizes in the monoclinic space group P 21/n with a = 13.8713(9) Å, b = 12.1365(6) Å, c = 21.5499(15) Å. The Pd atom has a slightly distorted square planar coordination geometry. The molecules of the title compound are linked by C–H···Cl weak hydrogen bonds into two-dimensional sheets parallel to the (001) plane. In addition, the title compound was characterized by elemental analyses and NMR spectroscopy. 相似文献
16.
Ryoichi Kishi Aritoshi Matsuda Toshiaki Miura Kazunari Matsumura Kokoro Iio 《Colloid and polymer science》2009,287(5):505-512
We prepared thermo-responsive polymer hydrogels by γ-ray irradiation of aqueous solutions of N, N-diethylacrylamide at different temperatures below and above its lower critical solution temperature (LCST). Poly(N, N-diethylacrylamide) gel had a transparent and homogeneous structure when the radiation-induced polymerization and crosslinking
were carried out below the LCST (25 °C) of the polymer. On the other hand, cloudy and heterogeneous gels were formed at temperatures
above the LCST of the polymer (>35 °C). From environmental scanning electron microscopy observations, the gels prepared at
35 and 40 °C were seen to show sponge-like bi-continuous porous structures, while those prepared at 50 °C showed a porous
structure consisting of interconnected microspheres. For temperature changes between 10 and 40 °C, gels with porous structures
showed rapid volume transitions on a time scale of about a minute, not only for shrinking but also for swelling processes,
which is in remarkable contrast to the porous poly(N-isopropylacrylamide) hydrogels. 相似文献
17.
Jian-Tao Zhang Xiang-Li Liu Alfred Fahr Klaus D. Jandt 《Colloid and polymer science》2008,286(10):1209-1213
In this study, a new method was developed to prepare temperature-sensitive poly(N-isopropylacrylamide) microgels by free radical precipitation polymerization using siloxane coupling agent as the new crosslinker.
Ammonium persulfate acted as the initiator for the radical copolymerization as well as the catalyst for the hydrolysis/condensation
of the siloxane groups. The particle diameter and polydispersity of the microgels were measured by photon correlation spectroscopy
and the results display that the microgels are monodisperse. The microgels exhibit temperature sensitivity and the phase transition
temperature is approximately 31 °C. Furthermore, the diameter of the microgels changes upon heating and cooling processes.
These were observed to be reversible. The novel crosslinking method described herein is the condensation of siloxane groups,
which is totally different from the traditional double-vinyl crosslinkers. This innovative approach offers an alternative
path to prepare functional core–shell particles and inorganic/organic hybrid materials. 相似文献
18.
Paramasivam Parthiban Mannangatty Rani Senthamaraikannan Kabilan 《Monatshefte für Chemie / Chemical Monthly》2009,49(3):287-301
Abstract A series of variously substituted N-methylpiperidin-4-one-O-benzyloximes were synthesized by three different methods. Among them, the direct conversion of 2,6-diarylpiperidin-4-ones
into the corresponding oxime ethers (method A) was proved to be better than the other two methods in the sense of good yield,
convenience, easy work-up and quick reaction time. All the synthesized compounds are characterized by IR, Mass and NMR (1H NMR, 13C NMR, 1H-1H COSY, 1H-13C COSY and HMBC) spectral studies. The conformational preference of the synthesized oxime ethers with/without alkyl and aryl
substituents at C-3/C-5 and C-2/C-6 is discussed using the spectral data. The observed chemical shifts and coupling constants
suggest that the synthesized oxime ethers adopt chair conformation with equatorial orientation of all the substituents, whereas
1-methyl-3-isopropyl-2,6-diphenylpiperidin-4-one-O-benzyloxime also exists in boat conformation. Based on the NMR data, the effects of oximination on ring carbons and their
associated protons and alkyl substituents are discussed. In addition, the effect of NMe group on the 2,6-diarylpiperidin-4-one-O-benzyloximes was also studied.
Graphical abstract
相似文献
19.
In order to design liposomes which release their contents in a glucose-sensitive manner, the surfaces of egg phosphatidylcholine
(egg PC) liposomes or dioleoylphosphatidylethanolamine (DOPE) liposomes were modified with the copolymer of N-isopropylacrylamide/methacrylic acid/octadecylacrylate and hydrophobically modified glucose oxidase (EC 1.1.3.4.). Whichever
the liposomes were prepared with egg PC or DOPE, an extensive release of calcein was observed at acidic conditions. And DOPE
liposomes were more pH sensitive than egg PC liposomes in terms of the release. In glucose-dependent calcein release experiment,
there was no release for 180 min when the suspension of liposome was free of glucose. When the glucose concentration was 50 mg/dl,
no appreciable amount of calcein was released for the first 50 min, but a significant release was observed for the last 130 min.
At glucose concentration of 200 mg/dl, calcein release became more extensive and the releases for 180 min from egg PC and
DOPE liposome were 84% and 98%, respectively. 相似文献
20.
Group-theoretical and quantum-chemical investigations of the spectrum of low-lying excited states have been performed by the ROHF and FCI-RAS (Full CI in Restricted Active Space) methods for 3d metal endofullerenes (MEFs) M@C60 (M =Mn, Cr, and Fe) in different charged states. The major purpose of this study is quantum-chemical verification of the anomalous (“non-Bethe’s”) character of splitting of the d N atomic states in an electrostatic field with icosahedral symmetry, predicted previously within the theory of integral invariants theory. The interrelation between the integral invariants theory and the quantumchemical methods applied in this work is considered in detail. Our calculations suggest that the d N atomic states in the icosahedral field generated by fullerene C60 (I h ) on a metal atom (ion) remain non-split for different charged states of the metal and C60. Reasons for this phenomenon and other possible approaches to verification of the prediction are discussed. It is demonstrated that the d N states of the encapsulated metal are split in icosahedral 3d MEFs only under very strong compression of these structures. 相似文献