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1.
Xiangrong Chen Xiaobin Ding Zhaohui Zheng Yuxing Peng 《Colloid and polymer science》2005,283(4):452-455
PNIPAAm-b-PPG-b-PNIPAAm triblock copolymers were prepared by redox polymerization. The self-assembly behavior and thermosensitive property of the copolymers in water were studied using 1H-NMR, TEM and a UV spectrophotometer. The results showed that the LCST of the copolymers was 32 °C, which was consistent with that of pure PNIPAAm. The copolymers could form a vesicular structure in an aqueous solution by self-assembly. The hollow structure of the PNIPAAm-b-PPG-b-PNIPAAm vesicles combined with the temperature-sensitive property may enable many potential applications of the vesicles. 相似文献
2.
Narrowly distributed polystyrene-g-p(N-isopropylacrylamide) (PSt-g-PNIPAM) was prepared by atom transfer radical polymerization (ATRP) of N-isopropylacrylamide using the brominated polystyrene as macroinitiator and CuCl combined with hexamethyltriethylenetetramine
as catalyst. Fourier transform infrared (FT-IR) spectroscopy and nuclear magnetic resonance (NMR) spectroscopy confirmed the
structure of PSt-g-PNIPAM. The gel permeation chromatography (GPC) showed that the graft copolymer had a single distribution
peak with molecular weight, M
n (g/mol) of 19815 g/mol (using polystyrene as the standard). Differential scanning calorimetry (DSC) revealed that due to
both effects of hydrophobic isopropyl groups and hydrogen bonds in the amide group, the glass transition temperature (T
g) of PSt-g-PNIPAM enhanced 16.0°C compared to the T
g of the polystyrene. 相似文献
3.
1H NMR spectra in CDCl3 of poly(N-vinylpyrrolidone), epoxidized poly(N-vinyl-pyrrolidone), and products derived from the latter by modification with amino acids (glycine, β-alanine, γ-aminobutyric
acid, and ε-aminocaproic acid) were examined. The 1H NMR spectra of the modified polymers contain signals for water protons due to different centers of water sorption. These
signals differ in chemical shift and integral intensity and indicate a changed spatial packing of the polymer as the result
of its modification.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2377–2380, October, 2005. 相似文献
4.
Jinghong Ma Yajing Xu Qingsong Zhang Liusheng Zha Borun Liang 《Colloid and polymer science》2007,285(4):479-484
A new kind of pH- and temperature-responsive semi-interpenetrating polymer network hydrogel based on linear carboxymethylchitosan
(CMCS) and poly (N-isopropylacrylamide) (PNIPA) crosslinked by inorganic clay was prepared. The pH-and temperature-responsive behaviors, the
deswelling kinetics, and the mechanical properties of the hydrogel were investigated. The hydrogels exhibited a volume phase
transition temperature around 33 °C with no significant deviation from the conventional PNIPA hydrogels. The results of the
influence of pH value on the swelling behaviors showed that the minimum swelling ratios of the hydrogels appeared near the
isoelectric point (IEP) of CMCS, and when pH deviated from the IEP, the hydrogels behaved as polycations or polyanions. The
novel hydrogels had much higher response rate than the conventional CMCS/PNIPA hydrogels. Moreover, the semi-IPN hydrogels
crosslinked by clay could be elongated to more than 800% and the elongation could be recovered almost completely and instantaneously. 相似文献
5.
《European Polymer Journal》2004,40(8):1931-1946
Two series of random copolymers of N-isopropylacrylamide (NIPAAm) and comonomers derived from methacrylic acid with a different number of methylene units as hydrophobic spacers (n=4, 7 and 10) were synthesized via free radicals. The first series was prepared having the acid groups methoxy-protected while the second series have the acid groups free. The NIPAAm-copolymers of both series were prepared varying the comonomer content from 5 to 20 mol%. All the copolymers were characterized by FTIR, DSC, 1H NMR and SLS. The aqueous solution behaviour of the copolymers having methoxy-protected acid groups shows that the comonomer increases the hydrophobicity of the copolymer chain and decreases its lower critical solution temperature (LCST). For the copolymers having free acid groups, hydrogen-bonding is responsible for a further decrease in the LCST of these copolymers in pure water. In buffer solutions, every acid comonomer have a critical ionization degree (αcrit) above which the LCST increases with increasing comonomer content while at an ionization degree lower than αcrit the LCST decreases with increasing comonomer content. In dependence of comonomer content, number of methylene units in the spacer and the pH of the buffer solution, the LCST of the copolymers can be varied widely, showing that these random copolymers have pH-tunable temperature sensitivity. 相似文献
6.
In this paper we present the findings of our investigations using molecular dynamics, on molecularly thin films of n-octane confined between topographically smooth solid surfaces. We focus on the effect of increasing solid surface-methylene unit energetic affinity and the effect of increasing pressure (normal load) of the film in inducing liquid-solid phase transitions. We observed an abrupt transition in the structural features of the film at a critical value of the characteristic energy that quantified the affinity between solid surfaces and methylene units. This energetically driven transition was evident from the discontinuous increase of intermolecular order, a precipitous extension of the octane molecules and freezing of molecular migration and rotation. Increasing pressure had a similar effect in inducing a liquid-solid phase transition. The characteristics of the transition showed that it is a mild first order transition from a highly ordered liquid to a poorly organized solid. These findings demonstrate that the solidification of nanoscopically thin films of linear alkanes is a general phenomenon (driven either energetically or by increasing pressure), and does not require the aid of commensurate surface topography. 相似文献
7.
Candan Erbil Bürgehan Terlan Özgür Akdemir Argun T. Gökçeören 《European Polymer Journal》2009,45(6):1728-1737
Copolymers of N-isopropylacrylamide (NIPAAm) and itaconic acid (IA) having various compositions were synthesized using free radical solution polymerization in 1,4-dioxane at 50 °C with α,α′-azobisisobutyronitrile (AIBN) as initiator. The structures of the copolymers were confirmed by Fourier transform infrared (FTIR) spectroscopic technique. The copolymer compositions were determined by conductometric and potentiometric methods from the inflection points in the acid-base titration curves and by FTIR spectroscopy through recorded analytical absorption bands for NIPAAm (1620 cm−1 for CO stretching of secondary amides) and for IA (1704 cm−1 for CO stretching) units, respectively. Monomer reactivity ratios of IA (F1)-NIPAAm (F2) pair were estimated using the Finemann-Ross, the inverted Finemann-Ross, the Kelen-Tüdós and the extended Kelen-Tüdós graphical methods. The values ranged from 0.40 to 0.60 for r1 and from 1.20 to 1.90 for r2, depending on the conversion percentage, calculation methods of monomer reactivity ratios and determination methods of copolymer compositions. In all cases, r1r2 < 1 and r1 < r2 indicate the random distribution of the monomers in the final copolymers and the presence of higher amount of NIPAAm units in the copolymer than that in the feed, respectively. 相似文献
8.
Iliyana V. Berlinova Ivaylo V. Dimitrov Ivan Gitsov 《Journal of polymer science. Part A, Polymer chemistry》1997,35(4):673-679
The synthesis of novel amphiphilic star-graft (SG) copolymers containing hydrophilic poly(oxyethylene) (PEO) side chains attached to a hydrophobic backbone by multifunctional entity is reported. In a first step poly(phthalimidoacrylate-co-styrene) was converted into polymers containing different number of multifunctional branching cites distributed along the main chain by partial aminolysis of the phthalimidoacrylate units with tris(hydroxymethyl)aminomethane. In the second step, these reactive copolymers yielded SG copolymers with different number of star-shaped PEO side groups by reaction with isocyanato terminated methoxy–PEO. The copolymers were characterized by size-exclusion chromatography, IR-, and NMR-spectroscopy. Their thermal properties were examined by thermal gravimetric analysis and differential scanning calorimetry. The studies indicate that the grafting degree and hydrogen bonding determine to a great extent the behavior of the SG copolymers in solid state and in solution. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 673–679, 1997 相似文献
9.
Frederic Eeckman 《European Polymer Journal》2004,40(4):873-881
Poly(N-isopropylacrylamide) (PNIPAAm) copolymers were synthesized in order to obtain co-polymers with a phase transition temperature slightly higher than the physiological temperature, as required by a new drug delivery concept described in a previous paper. Six hydrophilic comonomers bringing about a rise of the phase transition temperature were evaluated. The synthesized copolymers were characterized and the influence of the type and of the amount of the used comonomer on the phase transition temperature was discussed. Among the comonomers, Acrylamide (AAm), N-methyl-N-vinylacetamide (MVA), N-vinylacetamide (NVA), and N-vinyl-2-pyrrolidinone (VPL) were found to be capable to raise the phase transition temperature to a value slightly higher than 37 °C and to have adequate phase transition behavior. The selected four copolymers were subjected to an additional purification step that should make them fit to use as a controlling agent in drug delivery systems. 相似文献
10.
Polyacrylate gels such as: N-isopropylacrylamide (NIPA), ionic copolymer NIPA-co-sodium acrylate (NIPA-co-SA) and ionic copolymer NIPA-co-[2-(acryloyloxy)ethyl]trimethylammonium chloride (NIPA-co-XCl) were swollen by methanol, ethanol and N,N-dimethylformamide. These solvents were oxidized voltammetrically in the gels at platinum microelectrodes. The blocking coefficients, defined as the ratio of the currents observed in the presence and absence of the polymeric chains, were different for the solvents in the charged and uncharged polymers and did not differ for the electroactive probe, ferrocene, present in the solvents at millimolar level. This may mean that the micro ionic layer that is formed at microelectrodes at the plateau of the voltammetric solvent waves leads to a kind of collapse/phase transition of the polymer in the depletion layer. For methanol, the gel structure was found to prevent occasionally the formation of large gas bubbles at the potentials positive versus the first wave and then three one-electron waves could be obtained. Experiments done with a capillary cell and an optical microscope indicated that before formation of large bubbles at the Pt microelectrode a very dynamic, dense stream of microbubbles leaves the electrode surface.Dedicated to Zbigniew Galus on the occasion of his 70th birthday 相似文献
11.
Poly(N-isopropylacrylamide)/poly[(N-acetylimino)ethylene] thermosensitive block and graft copolymers
Block and graft copolymers with poly(N-isopropylacrylamide) and poly[(N-acetylimino)ethylene] (PNAI) sequences were synthesized via PNAI derivatives (macroinitiators or macromers). The polymerization yields for block copolymers synthesized in ethanol, using the PNAI macroinitiator, were low (<10%), except where photochemical polymerization was applied. By contrast, for the copolymerizations of N-isopropylacrylamide with the PNAI macromers, performed in alcoholic solution, quite high polymerization yields, around 80-90%, were reached. 1H-NMR and IR spectral and differential scanning calorimeter thermal data confirmed the copolymer formation. Thermosensitivity of the copolymers was investigated by means of turbidimetric technique as a function of their nature, average molecular weight and composition. It was found that the length of the chain of the PNAI macromer and the content in hydrophilic PNAI units of the resulted copolymer affected this behavior. 相似文献
12.
A systematic study of the dynamic shear modulusG
*=G+G in three poly(alkyl methacrylates) (PEMA, PnPMA, PnBMA) at frequencies between 0.001 and 500 rad/s is presented. As the splitting frequencies s are low, aging effects can be observed in the splitting region. There is a systematic shift of the splitting frequency s to lower values with increasing length of the alkyl side group. In PnBMA a separate shear appearance is observed about two frequency decades below the local mode . This is discussed in terms of the concept of minimal cooperativity. Aging effects are: Shift of the maximum loss frequency to lower values, peak sharpening of the relaxation, and intensity changes of and . These effects are discussed in terms of the sequential aging concept. Aging leads to a pronounced bending of the traces upwards from the equilibrium line in the Arrhenius diagram. These non-equilibrium phenomena are promoted by the small slope m=d(log )/dT of the trace in the splitting region.Dedicated to Prof. E. W. Fischer at the occasion of his 65th Birthday Lieber Herr Fischer, die Hallenser Polymerphysiker danken Ihnen aufrichtig für die warmherzige und effektive Förderung der Polymerwissenschaften im Raum Halle-Merseburg. 相似文献
13.
Reversible film formation process from nano-sized Poly(N-isopropylacrylamide) (PNIPAM) microgel particles were studied during heating-cooling cycles at various rates. Photon transmission
technique was used and transmitted photon intensity I
tr was monitored during heating–cooling cycles. The increase and decrease in I
tr during heating and cooling was explained with the void closure and void reconstruction processes, and the corresponding activation
energies were measured. It was observed that PNIPAM microgels required less energy during reconstruction of voids than their
closure. 相似文献
14.
Fabrication of novel thermo-responsive electrospun nanofibrous mats and their application in bioseparation 总被引:1,自引:0,他引:1
To fulfill the development of biotechnology and biomedicine, environmental-responsive polymer materials are wanted for isolation and purification of biomolecules. Herein, a novel thermo-responsive poly(methyl methacrylate) (PMMA)/poly(N-isopropylacrylamide) (PNIPAM) blend nanofibrous mat was developed, which can adsorb and release a model solute, bovine serum albumin (BSA), through the way of hydrophilicity–hydrophobicity transition behavior of PNIPAM. The uniform bead-free electrospun nanofibers were obtained from the homogeneous PMMA solution in the presence of different amount of PNIPAM. Scanning electron microscopy (SEM) analysis showed that the electrospinnability of PMMA was improved by the addition of PNIPAM, and the diameter of resultant nanofibers could be modulated by controlling the amount of PNIPAM. The thermo-responsive swelling behavior of the blend nanofibrous mats was reversible and reproducible by changing environmental temperature across the lower critical solution temperature (LCST) of PNIPAM. Moreover, the separation property of the blend nanofibrous mats was found to be related to the amount of PNIPAM as well as the concentration of BSA. As for a better separation effect, the nanofibers with higher content of PNIPAM were favorable. 相似文献
15.
Egg phosphatidylcholine (PC) liposomes bearing pH-sensitive polymers and dioleoylphosphatidylethanolamine (DOPE) liposomes
including the same polymers were prepared by a sonication method. As pH-sensitive polymers, copolymers of N-isopropylacrylamide, methacrylic acid, and octadecylacrylate were used. The liposomes were stable in neutral pH ranges in
terms of release. But the release became marked at pH 5.5, and it was accelerated as pH further decreased. For example, the
degree of release from egg PC liposomes (polymer/lipid ratio is 3:10, w/w) for 120 s increased from 2% to 63% as pH decreased from 7.5 to 4.5. Under the same condition, the degree of release from
DOPE liposomes increased from 4% to 80%. These results indicate that DOPE liposome is more pH-sensitive than egg PC liposome. 相似文献
16.
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
17.
Mika Furukawa Raymond S. Farinato Etsuo Kokufuta 《Colloid and polymer science》2008,286(12):1425-1434
This study aimed to investigate the effect of COOH group distribution within a polymer network having amide groups, with which
the COOH could form hydrogen bonds. We employed here two polyelectrolyte gels composed of N-isopropylacrylamide (NIPA) networks, either copolymerized with acrylic acid (AA) or within which poly(acrylic acid) (PAA)
was entrapped. Both gels (AA–NIPA ∼ 1:4 mol/mol) were prepared by aqueous red-ox polymerization with N,N’-methylenebisacrylamide as the cross-linker. Finely divided gels in NaCl solutions (0.025 and 0.1 M) were titrated with NaOH
and back-titrated with HCl at 25 °C. The results of the copolymer gel (CG) agreed well with those of a linear copolymer and
a nanoscale gel which had a similar AA content to CG. However, marked differences were observed in the titration behaviors
of the AA-copolymerized and PAA-entrapped gels, mainly due to the hydrogen bonding between the entrapped PAA chain and its
surrounding NIPA network. 相似文献
18.
Solutions of poly(N-isopropylacrylamide) (PNIPA) with ionic and nonionic surfactants were investigated by light scattering methods at temperatures
15–45 °C. In contrast to previous studies, where surfactants were used in excess, lower concentrations of surfactants were
used. The formation of well-defined nanoparticles of PNIPA was observed on heating above the lower critical solution temperature.
The effect of PNIPA and surfactant concentrations, and molecular weight of PNIPA on nanoparticle parameters and on the phase
transition temperature of PNIPA solutions were investigated. An interpretation based on stabilization of PNIPA nuclei by surfactants
was suggested. 相似文献
19.
Temperature responsive copolymers of dextran grafted with poly(N-isopropylacrylamide) (Dex-g-PNIPAAM) were prepared by atom transfer radical polymerization (ATRP) in homogeneous mild conditions without using protecting group chemistry. Dextran macroinitiator was synthesized by reaction of dextran with 2-chloropropionyl chloride at room temperature in DMF containing 2% LiCl. ATRP was carried out in DMF:water 50:50 (v/v) mixtures at room temperature with CuBr/Tris(2-dimethylaminoethyl)amine (Me6TREN) as catalyst. Several grafted copolymers with well defined number and length of low polydispersity grafted chains were prepared. Temperature induced association properties in aqueous solution were studied as a function of temperature and polymer concentration by dynamic light scattering, fluorescence spectroscopy and atomic force microscopy (AFM). LCST, ranging from 35 to 41 °C, was significantly affected by number and length of grafted chains. The fine tuning of LCST around body temperature is an important characteristic not obtainable by conventional radical grafting of PNIPAAM. Well defined spherical nanoparticles were formed above the LCST of PNIPAAM. Hydrodynamic diameter was in the range 73-98 nm. 相似文献
20.
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