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1.
Rodrigo París 《Polymer》2009,50(9):2065-1226
A series of pH-responsive hydrogels based on N-isopropylacrylamide (N-iPAAm), methacrylic acid (MAA) and poly(ethylene glycol) monomethyl ether monomethacrylate macromonomer (PEGMEMA), P(N-iPAAm-co-MAA-co-PEGMEMA) random terpolymers, were synthesized and their swelling behaviour studied as a function of both monomer composition and previous swelling treatment. The swelling kinetic curves were followed using gravimetric, photographic and magnetic resonance imaging (MRI) techniques, which provide spatial and temporal resolution. The swelling behaviour was non-Fickian at pH 7, being this fact more relevant when the samples were pre-soaked in pH 2 solution. Low pH promotes hydrogen bond arrangements that disrupt at pH 7, where sigmoidal swelling curves were observed. The sigmoidal shape of the curves increases as well as the swelling time with increasing N-iPAAm/PEGMEMA ratio. This indicates that hydrogen bond arrangements between MAA and N-iPAAm are stronger that those formed by MAA and PEGMEMA. The influence of the polymer composition on the hydrogen bond arrangements was also studied from the swelling kinetics curves at different pH media, observing that the swelling rate, the swelling curve shape and the whole amount of water absorbed were clearly dependent on this parameter. 相似文献
2.
The influence of the swelling history on the swelling behavior of poly[(N-isopropylacrylamide)-co-(methacrylic acid)] P[(N-iPAAm)-co-(MAA)] random copolymers hydrogels synthesized by free radical polymerization in solution of N-iPAAm and MAA comonomers crosslinked with tetraethylene glycol dimethyl acrylate (TEGDMA) has been studied. The swelling behavior under pH 7 at 18, 29, 39 and 49 °C of this series of copolymers, previously soaked either at pH 2 or 7 has been investigated. The swelling kinetics of these two series of samples displays different behavior as function of the composition and temperature. However, the equilibrium swelling values only show slight dependences on the previous soaking pH and temperature. When samples are soaked at pH 7, then the swelling at pH 7 follows a first order kinetics, irrespective of the copolymer composition or the temperature at which the experiment has been carried out. In this case, the swelling process is very fast and depends only slightly on temperature. The first order rate constant increases with the MAA content in the hydrogel. Furthermore, the swelling rate of copolymer hydrogels soaked at pH 2, show strong dependence on composition and temperature. They follow an autocatalytic swelling kinetics due to the disruption of hydrogen bond arrangements. An initial slow water uptake is followed by an acceleration process, in which water molecules inside the gel help the next water molecules to come in. Two rate constants, a first-order rate constant and an autocatalytic one have been obtained from the kinetics analysis. They have revealed different temperature dependence which may be due to a balance between hydrophobic and hydrogen bond interactions. The temperature dependence of the swelling kinetics is stronger and more complex for copolymers treated under pH 2 than for copolymers soaked under pH 7. 相似文献
3.
In this paper, novel thermosensitive poly(N-isopropylacrylamide) (PNIPAM) nanocapsules with temperature-tunable diameter and permeability are reported. Firstly, the core-shell composite microparticles were synthesized by precipitation polymerization with isothiocyanate fluorescein (FITC) entrapped SiO2 as core and cross-linked PNIPAM as shell. Then, the SiO2 core was etched by hydrofluoric acid at certain condition and the pre-trapped FITC molecules remained within the inner cavity. The FITC release profile and TEM studies clearly indicate that the release behavior of FITC could be controlled effectively by the external temperature. Above the LCST of PNIPAM (32 °C), the dehydrated PNIPAM shell inhibited the release of FITC from the internal cavity while below its LCST, the fluorophore could permeate the swollen shell easily. 相似文献
4.
Dirk Kuckling Jan HoffmannMatthias Plötner Dirk FerseKatja Kretschmer Hans-Jürgen P AdlerKarl-Friedrich Arndt Rudolf Reichelt 《Polymer》2003,44(16):4455-4462
Micro-fabricated temperature responsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels were produced by photolithographic patterning of photo cross-linkable polymers. These polymers were synthesized by copolymerization of N-isopropylacrylamide (NIPAAm) and 2-(dimethyl maleimido)-N-ethyl-acrylamide (DMIAAm). The patterning process of polymers with 9.2 mol% DMIAAm and film thickness below 5 μm in the dry state was able to depict a lateral resolution of 4 μm with insignificant shape change. In order to increase the adhesion of the swollen hydrogels, and thus, the resolution of a particular pattern, a special adhesion promoter based on a monochlorosilane anchor group and a chromophore head group was synthesized. If a silicon wafer surface was pretreated with the adhesion promoter, the structures were stable and well adhered even at lower cross-linking densities. The hydrogels are suitable as working substances for micro-actuators because of their thermally induced volume changes. The swelling ratio of the pattern at low temperatures increased with a decreased cross-linking density. As expected from the chemical composition of the gels, the phase transition temperature (Tc) decreased with increasing DMIAAm content. The swelling of microstructures in water in comparison to macroscopic objects occured significantly faster. This behavior was attributed to the small gel dimension but it was even more pronounced because of the sponge-like nanostructure of the hydrogels characterized by high-resolution field emission scanning electron microscopy. Suitable applications of these hydrogels are adjusting limbs in fluid micro-systems such as micro-pumps and micro-valves. 相似文献
5.
Wei XueIan W Hamley 《Polymer》2002,43(10):3069-3077
Hydrogels were prepared by free radical polymerisation in aqueous solution of N-isopropylacrylamide (NIPA) and of NIPA with di-n-propylacrylamide (DPAM), di-n-octylacrylamide (DOAM) or di-dodecylacrylamide (DDAM) as hydrophobic comonomer. N,N-methylene bisacrylamide (BIS) and glyoxal bis(diallyacetal) (GLY) were used as crosslinkers. A series of copolymers with three different comonomer contents was synthesised and for some polymers three different crosslinker concentrations were employed. The swelling equilibrium of these hydrogels was studied as a function of temperature, hydrophobic comonomer species and content in aqueous solutions of the anionic surfactant sodium dodecyl sulfate (SDS). In pure water the gels showed a discontinuous volume phase transition at 33 and 30 °C for PNIPA and hydrophobically modified PNIPA copolymeric hydrogels, respectively. The swelling ratio r and the transition temperature (LCST) increased at low temperatures with the addition of SDS, this is ascribed to the conversion of non-ionic PNIPA gels into polyelectrolyte gels through the binding of SDS. At SDS concentration below 0.5 wt%, gels exhibited a single discontinuous volume transition at 36-38 °C. However, for SDS concentration above 0.5 wt%, two discontinuous volume transitions at 36-40 and 70 °C were observed. Additionally, the replacement of BIS by the novel octafunctional crosslinker glyoxal bis(diallylacetal) (GLY) yielded an increase in the swelling ratio. 相似文献
6.
1H NMR spectroscopy was used to investigate temperature-induced phase transitions in D2O solutions of poly(N-isopropylmethacrylamide) (PIPMAm)/poly(N-isopropylacrylamide) (PIPAAm) mixtures and P(IPMAm/IPAAm) random copolymers of various composition on molecular level. While two phase transitions were detected for PIPMAm/PIPAAm mixtures, only single phase transition was found for P(IPMAm/IPAAm) copolymers. The phase transition temperatures of PIPAAm component (appears at lower temperatures) are not affected by the presence of PIPMAm in the mixtures; on the other hand, the temperatures of the phase transition of PIPMAm component (appears at higher temperatures) are affected by the phase separation of the PIPAAm component and depend on concentration of the solution. For P(IPMAm/IPAAm) random copolymers, a departure from the linear dependence of the transition temperatures on the copolymer composition was found for a sample with 75 mol% of IPMAm monomeric units. 相似文献
7.
Rapid response thermally sensitive hydrophobically modified poly(N-isopropylacrylamide) hydrogels have been synthesised successfully using a two-step polymerisation method, the initial polymerisation being carried out at 20 °C, followed by polymerisation at −28 °C for 24 h. The results show that the swelling/deswelling rates of poly[N-isopropylacrylamide-co-(di-n-propylacrylamide)] P(NIPA-co-DPAM) hydrogels prepared by two-step polymerisation are much faster than for the same type of hydrogels prepared via conventional methods (30 °C for 24 h), i.e. the time for the former xerogel to absorb 70 and 90 wt% is just 30 and 240 min, respectively, compared to the latter xerogel which takes 1600 and 2500 min to absorb the same amounts of water. During deswelling (shrinking), the hydrogel loses 95 wt% water in 1 min, compared to a timescale for the corresponding cross-linked copolymers prepared by conventional methods of about 5 h for 50 wt% water loss. Scanning electron microscopy, and flotation experiments together with swelling ratio studies reveal that the polymeric network of the former hydrogel is characterised by an open structure with more pores and higher swelling ratio but lower mechanical strength compared to the latter hydrogels. Such rapid response hydrogels have potential applications in separation and drug release technologies for example. 相似文献
8.
Ternary liquid–liquid phase transitions of linear poly(N-isopropylacrylamide) (PNIPA) and the swelling behavior of cross-linked PNIPA gels in water/2-propanol mixtures were investigated using thermo-optical analysis (TOA) and a photon correlation spectroscopy (PCS) technique, respectively. Closed immiscibility gaps in ternary phase diagrams were obtained below 35 °C although all binary mixtures involved in this system were completely miscible. At a fixed concentration of PNIPA (1.0 wt%), a decrease in the lower critical solution temperature (LCST) occurred first, and with an increasing 2-propanol fraction of the solvent mixture, the upper critical solution temperature (UCST) subsequently developed. Corresponding to the linear PNIPA solution behavior, swollen PNIPA gels in pure water first shrank and then reswelled with increasing 2-propanol content in a typical reentrant transition. For theoretical treatment of the mixtures, a multi-component lattice theory of mixing and Flory–Rehner chain model for elasticity were employed for molecular thermodynamic analysis. A secondary lattice concept of specific interactions was used to model binary water/PNIPA solutions, and a temperature dependence of the intermolecular interactions for 2-propanol/PNIPA was used to describe island type ternary phase diagrams. The swelling transitions of cross-linked PNIPA gels were calculated using model parameters obtained from the ternary phase diagrams of linear PNIPA or from experimental conditions. The predicted results were in good agreement with experimental data without the need for further adjustable parameters. 相似文献
9.
The coil-to-globule and globule-to-coil transition of poly(N-isopropylacrylamide) in aqueous solution had been studied by heating and cooling the sample solution with conventional viscosity measurement. A single chain collapsed globule solution was prepared firstly by adding sodium n-dodecyl sulfate (SDS) into the polymer solution at room temperature, as the chain collapsed to compact globule at higher temperature and then the SDS was removed by electro-dialysis. The viscosity data were analyzed in a quantitative way, which permitted to elucidate the transition temperature and the amount of the water in the collapsed globule precisely. 相似文献
10.
Fangping Yi 《Polymer》2009,50(2):670-198
Reversible addition-fragmentation chain transfer polymerization was employed to prepare the crosslinked poly(N-isopropylacrylamide)-graft-polystyrene networks (PNIPAAm-g-PS). Due to the immiscibility of PNIPAAm with PS, the crosslinked PNIPAAm-g-PS copolymers displayed the microphase-separated morphology. While the PNIPAAm-g-PS copolymer networks were subjected to the swelling experiments, it is found that the PS block-containing PNIPAAm hydrogels significantly exhibited faster response to the external temperature changes according to swelling, deswelling, and reswelling experiments than the conventional PNIPAAm hydrogels. The improved thermo-responsive properties of hydrogels have been interpreted on the basis of the formation of the specific microphase-separated morphology in the hydrogels, i.e., the PS blocks pendent from the crosslinked PNIPAAm networks were self-assembled into the highly hydrophobic nanodomains, which behave as the microporogens and thus promote the contact of PNIPAAm chains and water. The self-organized morphology in the hydrogels was further confirmed by photon correlation spectroscopy (PCS). The PCS shows that the linear model block copolymers of PNIPAAm-g-PS networks were self-organized into micelle structures, i.e., the PS domains constitute the hydrophobic nanodomains in PNIPAAm-g-PS networks. 相似文献
11.
A crown ether derivative (4′-allyldibenzo-18-crown-6, CE) was covalently incorporated into the network of temperature sensitive poly(N-isopropylacrylamide) (PNIPA) hydrogels by copolymerization in a mixed solvent of water and tetrahydrofuran (H2O/THF). The poly(N-isopropylacrylamide-co-4′-allyldibenzo-18-crown-6) (poly(NIPA-co-CE)) hydrogels exhibited dramatically faster deswelling rates than normal PNIPA hydrogels at a temperature (50 °C) above their lower critical solution temperatures. The effect of the solvent component ratio in the mixed solvent during the copolymerization on the swelling properties of the poly(NIPA-co-CE) hydrogel was investigated. The thermosensitive poly(NIPA-co-CE) hydrogels have potential applications in the extraction of cations and separation of chiral drugs. 相似文献
12.
Preparation temperature dependence of equilibrium swelling degree and shrinking kinetics of poly(N-isopropylacrylamide) gel has been investigated by optical microscopic measurements. The degree of swelling, d/d0, at 20 °C was found to be strongly dependent on the preparation temperature, Tprep, where d and d0 are the diameter of gel during observation and preparation, respectively. The value of d/d0 was about 1.2 for Tprep=20 °C, but steeply increased by approaching the phase separation temperature ≈32.0 °C. Above 32.0 °C, d/d0 decreases stepwise to 1.46. This upturn in d/d0 was correlated with spatial inhomogeneities in gels. That is, the gel became opaque by increasing Tprep. Though the shrinking half-time, t1/2, of gel was on the order of 500 min for Tprep≤20 °C, t1/2 decreased to 2 min for Tprep≥26 °C. Hence, a rapid shrinking was attained by simply increasing Tprep. The physical implication of this rapid shrinking in gels was discussed in conjunction with the gel inhomogeneities and a thermodynamic theory of swelling equilibrium. 相似文献
13.
Sang Chul Jung 《Polymer》2009,50(14):3370-10547
The closed-loop phase diagram of poly N-isopropylacrylamide (PNIPA) in a water-N,N-dimethylformamide (DMF) system was measured by thermooptical analysis (TOA). The reentrant swelling behavior of N-isopropylacrylamide (NIPA) nano-sized gel particles in the water-DMF system was measured by using photon correlation spectroscopy (PCS) technique. Theoretically, a modified double lattice model (MDL) can be used to describe the closed-loop phase behavior of linear PNIPA in water-DMF systems. For crosslinked NIPA nano-sized gel particles in a water-DMF system, we combined MDL theory for the mixing contribution and Flory-Erman theory for the elastic contribution. Molecular interaction parameters obtained from the PNIPA solution were used to directly predict the swelling-ratio curves for the NIPA gel. Using our model, the calculated results were in good agreement with the experimental data using only one adjustable parameter. 相似文献
14.
A reactive polymer of N-isopropylacrylamide (co-PNIPAAm) was prepared by copolymerization with a vinyl monomer carrying a protected isocyanate group. Thin layers of co-PNIPAAm were formed on a surface carrying hydroxyl groups using a spin-coater and were cross-linked and immobilized on the surface by heating. These layers were characterized by X-ray photoelectron spectroscopy, Fourier transform infrared spectroscopy, atomic force microscopy and surface plasmon resonance (SPR). The thickness of the co-PNIPAAm layers could be controlled from 4 to 35 nm by changing the concentration of the polymer solutions and the spin-coating conditions. Very little amount of γ-globulin was adsorbed onto the co-PNIPAAm layers even when thicknesses as low as 4 nm were analyzed. In addition, the swelling ratios of the co-PNIPAAm layers were about 4.6 and 1.3 at 25 °C and at 40 °C, respectively. These results indicate that the co-PNIPAAm can be very useful in preparing thermo-sensitive layers on substrates and thus various biomedical applications may be useful. 相似文献
15.
Grafting of poly(N-isopropylacrylamide) (PNIPAAm) having carboxylic groups at one end onto poly(allylamine) (PAH) in the presence of water soluble carbodiimide has yielded PAH-g-PNIPAAm copolymers with grafting ratios of 50, 29 and 18, respectively. These thermosensitive copolymers exhibit a lower critical solution temperature (LCST) at 34 °C at a temperature increase cycle regardless of their grafting ratios, a temperature identical to that of PNIPAAm-COOH oligomers. Temperature cycling reveals completely reversible polymer aggregation and dissolution above and below the LCST, respectively. Much smaller particle sizes are observed by scanning force microscopy and transmission electron microscopy compared to dynamic light scattering. A porous sphere model is suggested to depict the structure of the particles formed above the LCST, by which the dependence of the particle sizes on their grafting ratios is interpreted taking into account the surface tension and the spatial aggregation distance. Finally, to demonstrate the capability of the copolymers being used as thermosensitive polyelectrolytes, assembly onto multilayers is conducted and the increase of layer thickness is confirmed by small angle X-ray scattering and ellipsometry characterizations. 相似文献
16.
In this study, the swelling behaviour of copolymer hydrogels of N-isopropylacrylamide (NIPAM) and itaconic acid (IA) in response to temperature and pH value of the external media was studied. The equilibrium degree of swelling for PNIPAM and PNIPAM/IA copolymers was greater at 25 °C than at 37 °C. The degree of swelling was low at low pH values. As the degree of ionization increased above the nominal pKa values of IA, the increased hydrophilicity resulted in larger degrees of swelling. At 37 °C, the PNIPAM hydrogel and some copolymers show anomalous swelling behaviour, i.e. the overshooting effect, in buffered solutions of certain pH values. A swelling-deswelling study showed that the deswelling process of the hydrogels was faster then the swelling process. According to dynamic swelling studies, the diffusion exponent and the diffusion coefficient both increase with increasing content of IA. 相似文献
17.
Thermosensitive poly(N-isopropylacrylamide) (PNIPAm) brushes grafted on SiO2-coated quartz crystal surface were prepared by the surface initiated radical polymerization. Using X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM), about 50 nm thickness of PNIPAm brushes were successfully formed. Quartz crystal microbalance with dissipation (QCM-D) is employed to investigate the collapse and swelling behavior of the PNIPAm brushes in water in real time. Both frequency and dissipation of PNIPAm layer were found to change gradually over the temperature range 15-50 °C, indicating that the brushes undergo a continuous transition. This continuous change is attributed to the nonuniformity and stretching of PNIPAm brushes as well as the cooperativity between collapse and dehydration transition. 相似文献
18.
19.
Self-assembly of poly(t-butyl acrylate-co-acrylic acid)-b-poly(N-isopropylacrylamide) [P(tBA-co-AA)-b-PNIPAM], which was obtained from part hydrolysis of PtBA-b-PNIPAM synthesized by sequential atom transfer radical polymerization (ATRP) was studied. Thermo- and pH-responsive core-shell-corona (CSC) micelles with different structures were formed from (PtBA-co-PAA)-b-PNIPAM in aqueous solution. At pH 5.8 and 25 °C, the block copolymer self-assembled into spherical core-shell micelles with hydrophobic PtBA segments as the core, hydrophilic PAA/PNIPAM segments as the mixed shell. Increasing temperatures, core-shell micelles converted into CSC micelles with PtBA as the core, collapsed PNIPAM as the shell and soluble PAA as the corona. Moreover, decreasing pH at 25 °C, PAA chains collapsed onto the core resulting in CSC micelles with PtBA as the core, PAA as the shell and PNIPAM as the corona. 相似文献
20.
Poly(vinylamine), the simplest polycation with primary amines, was applied to interpenetrating polymer networks (IPN) with poly(acrylic acid). N-Vinylformamide (NVF) was employed for amino-protected monomers to control electrostatic balance. pH-responsivities of IPNs varied, depending on the hydrolysis conditions and acrylic acid (AAc) concentration of the second network. Poly(N-vinylacetamide)-co-poly(N-vinylformamide) (4/6, mol/mol) was employed for the first network, subsequently hydrolyzed with 50% amide groups, and the second network was polymerized with 0.25 mol L−1 AAc, extremely shrunken hydrogels with polyion complex were formed at pH 7, showing that the controlled amount of highly active primary amines are available in IPN. 相似文献