腐植酸钠/聚丙烯酰胺/粘土杂化水凝胶的研究

以过硫酸钾为引发剂、N,N′-亚甲基双丙烯酰胺为交联剂、丙烯酰胺单体和腐植酸钠、Laponite RD粘土为原料,用溶液聚合交联法合成了腐植酸钠/聚丙烯酰胺/粘土(SH-PAM-Clay)系列水凝胶.用场发射扫描电镜对其表面形貌进行了研究,并对水凝胶的吸水性和流变性能进行了测试和研究.结果表明这系列水凝胶都具有致密的网络结构和优良的吸水性能.     

Preparation and characterization of sodium carboxymethylcellulose/poly(N-isopropylacrylamide)/clay semi-IPN nanocomposite hydrogels

A new kind of pH-/temperature-responsive semi-interpenetrating polymer network hydrogels based on linear sodium carboxymethylcellulose (CMC) and poly(N-isopropylacrylamide) (PNIPA) cross-linked by inorganic clay (CMC/PNIPA/Clay hydrogel) was prepared. The temperature- and pH-responsive behaviors, the mechanical properties of these hydrogels were investigated. The CMC/PNIPA/Clay hydrogels exhibited a volume phase transition temperature around 32 °C with no significant deviation from the conventional PNIPA hydrogels. The swelling ratio of the CMC/PNIPA/Clay hydrogels gradually decreased with increasing the contents of clay. The influence of pH value on swelling behaviors showed that there is a maximum swelling ratio at pH 5.9. Moreover, the CMC/PNIPA/Clay hydrogels exhibited excellent mechanical properties with high tensile stress and elongation at break in excess of 1200%.     

Effects of synthesis-solvent on swelling and elastic properties of poly(N-isopropylacrylamide) hydrogels

Thermosensitive N-isopropylacrylamide (NIPA) hydrogels were synthesized by a free radical copolymerization with N,N′-methylenebisacrylamide (MBAA) in four solvents: water, ethanol, acetone and N,N-dimethylformamide. The swelling and elastic properties of the hydrogels were affected by the synthesis-solvents; the hydrogels (e.g. NIPA/MBAA = 1000/50 mol/m³-pre-gel solution) synthesized in water have smaller swelling volume and larger shear modulus at 10 °C than those synthesized in amphiphilic solvents. The network structure of hydrogels was estimated in terms of the conversion and two sorts of effective crosslinking density based on the Flory theory and the concentration of crosslinker. The hydrogels synthesized in water can have the microscopic inhomogeneous network arising from the entanglement of polymer chains, while the hydrogels synthesized in amphiphilic solvents can have the homogeneous network arising from the polymer concentration lower than the pre-gel solution and can be similar in network structure to the lightly crosslinked hydrogel synthesized in water.     

pH-thermoreversible hydrogels. I. Synthesis and characterization of poly(N-isopropylacrylamide/maleic acid) copolymeric hydrogels

N-isopropylacrylamide (NIPAAM)/maleic acid (MA) copolymeric hydrogels were prepared by irradiating the ternary mixtures of NIPAAM/MA/Water by γ-rays at ambient temperature. The influence of external stimuli such as pH and temperature of the swelling media on the equilibrium swelling properties was investigated. The hydrogels showed both temperature and pH responses. The effect of comonomer concentration and irradiation dose on the swelling equilibria and phase transition was studied. For the characterization of these hydrogels, the diffusion behaviour and molecular weight between crosslinks were investigated.     

Graphene Oxide/Polyacrylamide/Aluminum Ion Cross‐Linked Carboxymethyl Hemicellulose Nanocomposite Hydrogels with Very Tough and Elastic Properties

Development of high‐strength hydrogels has recently attracted ever‐increasing attention. In this work, a new design strategy has been proposed to prepare graphene oxide (GO)/polyacrylamide (PAM)/aluminum ion (Al³⁺)‐cross‐linked carboxymethyl hemicellulose (Al‐CMH) nanocomposite hydrogels with very tough and elastic properties. GO/PAM/Al‐CMH hydrogels were synthesized by introducing graphene oxide (GO) into PAM/CMH hydrogel, followed by ionic cross‐linking of Al³⁺. The nanocomposite hydrogels were characterized by means of FTIR, X‐ray diffraction (XRD), and scanning electron microscopy/energy‐dispersive X‐ray analysis (SEM‐EDX) along with their swelling and mechanical properties. The maximum compressive strength and the Young's modulus of GO_3.5/PAM/Al‐CMH_0.45 hydrogel achieved values of up to 1.12 and 13.27 MPa, increased by approximately 6488 and 18330 % relative to the PAM hydrogel (0.017 and 0.072 MPa). The as‐prepared GO/PAM/Al‐CMH nanocomposite hydrogels possess high strength and great elasticity giving them potential in bioengineering and drug‐delivery system applications.     

Biodegradable and pH-sensitive hydrogels: Synthesis by crosslinking of N,N-dimethylacrylamide copolymer precursors

Novel pH-sensitive hydrogels containing azoaromatic crosslinks were synthesized by the crosslinking of polymeric precursors. First, a reactive polymeric precursor was synthesized by copolymerization of N,N-dimethylacrylamide, N-tert-butylacrylamide, acrylic acid, and N-methacryloylglycylglycine p-nitrophenyl ester. The hydrogel was prepared in the second step by the reaction of the polymeric precursor with N,N′-(ω-aminocaproyl)-4,4′-diaminoazobenzene. The hydrogels were characterized by the network structure, (that is, content of crosslinks, unreacted pendent groups, and cycles), the equilibrium swelling ratio as a function of pH, modulus of elasticity in compression, and the degradability in vitro. The results obtained indicated that the hydrogel network structure strongly depends on the reaction conditions such as polymer concentration, and the ratio of the reactive groups during the crosslinking reaction. The swelling and mechanical properties of hydrogels can be controlled by the modification of polymer backbone structure and/or the crosslinking density. The rates of hydrogel degradation depended on their degree of swelling. The higher the degree of swelling, the higher the degradability. The properties of the hydrogels suggest that they have a potential as carriers for colon-specific drug delivery. © 1994 John Wiley & Sons, Inc.     

Preparation and characterization of pH- and temperature-responsive semi-IPN hydrogels of carboxymethyl chitosan with poly (<Emphasis Type="Italic">N</Emphasis>-isopropyl acrylamide) crosslinked by clay

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.     

Synthesis and characterization of thermoresponsive isopropylacrylamide-acrylamide hydrogels

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.     

Fast responsive poly(N-isopropylacrylamide) hydrogels prepared in phenol aqueous solutions

Fast responsive poly(N-isopropylacrylamide) (PNIPAAm) hydrogels with improved properties were prepared in phenol aqueous solutions with different concentrations. Due to the expanded network structure in water, the resulted hydrogels are capable of absorbing a large amount of water, i.e. exhibits a much increased swelling ratio at room temperature. Importantly, the hydrogels demonstrated much faster response rate than that of traditional PNIPAAm hydrogel upon external temperature increase.     

Thermosensitive poly(N-isopropylacrylamide-co-acrylamide) hydrogels: Synthesis, swelling and interaction with ionic surfactants

Thermosensitive hydrogels were prepared by free-radical polymerization in aqueous solution from N-isopropylacrylamide (NIPA) and acrylamide (AAm) monomers. N,N-Methylenebis(acrylamide) (MBAAm) was used as a crosslinker. A kinetic study of the absorption determined the transport mechanism. The diffusion coefficients of these hydrogels were calculated for the Fickian mechanism. It was shown that the swelling behavior of the P(NIPA-co-AAm) hydrogels can be controlled by changing the amount of MBAAm. The swelling equilibrium of the P(NIPA-co-AAm) hydrogels was also investigated as a function of temperature in aqueous solutions of the anionic surfactant sodium dodecyl sulfate (SDS) and the cationic surfactant dodecyltrimethylammonium bromide (DTAB). In SDS and DTAB solutions, the equilibrium swelling ratio of the hydrogels increased, this is ascribed to the conversion of non-ionic P(NIPA-co-AAm) hydrogel into polyelectrolyte hydrogels due to binding of surfactant molecules through the hydrophobic interaction. Additionally, the amount of free SDS and DTAB ions was measured at different temperatures by a conductometric method, it was found that the electric conductivity of the P(NIPA-co-AAm)—surfactant systems depended strongly on both the type and concentration of surfactant solutions.     

Radiation synthesis and characterization of poly(N,N-dimethylaminoethyl methacrylate-co-N-vinyl 2-pyrrolidone) hydrogels

In this study, radiation synthesis and characterization of swelling behavior and network structure of poly(N,N-dimethylaminoethyl methacrylate) (PDMAEMA), and poly(N,N-dimethylaminoethyl methacrylate-co-N-vinyl 2-pyrrolidone) (P(DMAEMA-co-VP)), hydrogels were investigated. PDMAEMA and P(DMAEMA-co-VP) hydrogels in the rod forms were prepared by irradiating the ternary mixtures of DMAEMA/VP/cross-linking agent, ethyleneglycol dimethacrylate (EGDMA), by gamma rays at ambient temperature. In composition ranges where the three components were completely miscible, water was also added to the ternary mixture to provide the formation of homogeneous polymerization and gelation. The influence of irradiation dose, comonomer, VP, and cross-linking agent, EGDMA, content on the total percentage gelation and monomer conversion were investigated. The effect of pH and temperature on the swelling behavior of hydrogels have also been examined. Hydrogels showed typical pH response and temperature responses, such as low-pH and low temperature swelling and high-pH and high temperature deswelling. Polymer-solvent interaction parameter (χ) and enthalpy and entropy changes appearing in the χ parameter for the P(DMAEMA-co-VP)-water system were determined by using Flory-Rehner theory of swelling equilibrium. The negative values for ΔH and ΔS indicate that prepared pure PDMAEMA and P(DMAEMA-co-VP) hydrogels have lower critical solution temperature (LCST) and Flory-Rehner theory of swelling equilibrium provides a satisfactory agreement to the experimental swelling data of the hydrogels.     

Swelling behavior of ionically cross-linked polyampholytic hydrogels in varied salt solutions

Ionically cross-linked polyampholytic hydrogels were synthesized by redox copolymerization of acrylamide and an ionic complex of (N,N-diethylamino)ethyl methacrylate and acrylic acid (designated as PADA hydrogel). The swelling behavior of the hydrogels in water indicated that a minimal equilibrium swelling ratio is found when the molar ratio of anionic/cationic monomers was 1.55. In NaCl solution, the hydrogels exhibited the typical swelling behavior of conventional polyampholytic gels. Their equilibrium swelling ratios increased with an increase in the NaCl concentration. In solutions of multivalent ions (CaCl₂ and trisodium citrate solutions), the equilibrium swelling ratios of the hydrogels increased first and were then followed by a decrease with an increase in salt concentration. Interestingly, an unexpected abrupt swelling phenomenon was observed when the fully swollen hydrogels in salt solution were transmitted to pure water. The unique swelling behavior of PADA hydrogels depends not only on the molar ratio of the anionic/cationic monomers but also on the valency of the ions.     

Thermoresponsive poly(N-isopropylacrylamide) nanogels/poly(acrylamide) nanostructured hydrogels

Here we report the preparation and characterization of nanostructured thermo-responsive poly(acrylamide) (PAM)-based hydrogels. The addition of slightly crosslinked poly(N-isopropylacrylamide) (PNIPA) nanogels to AM reactive aqueous solution produces nanostructured hydrogels that exhibit a volume phase transition temperature (T_VPT). Their swelling kinetics, T_VPT's and mechanical properties at the equilibrium-swollen state (H_eq) are investigated as a function of the concentration of PNIPA nanogels in the nanostructured hydrogels. Nanostructured hydrogels with PNIPA nanogels/AM mass ratios of 20/80 and above exhibit higher H_eq and longer time to reach the equilibrium swelling than those of the conventional PAM hydrogels. However, the PNIPA nanogels possess thermo-responsive character missing in conventional PAM hydrogels. The T_VPT of nanostructured hydrogels depends on PNIPA nanogel content but their elastic and Young moduli are larger than those of conventional hydrogels at similar swelling ratios. Swelling kinetics, T_VPT, and mechanical properties are explained in terms of the controlled in-homogeneities introduced by the PNIPA nanogels during the polymerization.     

Novel poly(N‐isopropylacrylamide)/clay/poly(acrylamide) IPN hydrogels with the response rate and drug release controlled by clay content

Novel interpenetrating network (IPN) hydrogels (PNIPAAm/clay/PAAm hydrogels) based on poly(N‐isopropylacrylamide) (PNIPAAm) crosslinked by inorganic clay and poly(acrylamide) (PAAm) crosslinked by organic crosslinker were prepared in situ by ultraviolet (UV) irradiation polymerization. The effects of clay content on temperature dependence of equilibrium swelling ratio, deswelling behavior, thermal behavior, and the interior morphology of resultant IPN hydrogels were investigated with the help of Fourier transform infrared spectroscopy, differential scanning calorimeter (DSC), scanning electron microscope (SEM). Study on temperature dependence of equilibrium swelling ratio showed that all IPN hydrogels exhibited temperature‐sensitivity. DSC further revealed that the temperature‐sensitivity was weakened with increasing amount of clay. Study on deswelling behavior revealed that IPN hydrogels had much faster response rate when comparing with PNIPAAm/clay hydrogels, and the response rate of IPN hydrogels could be controlled by clay content. SEM revealed that there existed difference in the interior morphology of IPN hydrogels between 20 [below lower critical solution temperature (LCST)] and 50 °C (above LCST), and this difference would become obvious with a decrease in clay content. For the standpoint of applications, oscillating swelling/deswelling behavior was investigated to determine whether properties of IPN hydrogels would be stable for potential applications. Bovine serum albumin (BSA) was used as model drug for in vitro experiment, the release data suggested that the controlled drug release could be achieved by modulating clay content. © 2008 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 47: 96–106, 2009     

The preparation and properties of hybridized hydrogels based on cubic thiol-functionalized silsesquioxane covalently linked with poly(N-isopropylacrylamide)

Firstly, nano-sized polyhedral oligomeric silsesquioxane with functional mercapto groups (POSS-SH) was prepared through hydrolytic condensation of 3-mercaptopropyl trimethoxysilane. Then N-isopropylacrylamide (NIPAm) was allowed to polymerize at the presence of POSS-SH and N,N-methylene-bisacrylamide to yield hybridized hydrogels. The hybridized hydrogels demonstrated thermosensitive behavior across the volume phase transition temperatures. The swelling and deswelling rates were greatly accelerated through the incorporating of POSS-SH into the gels, and the thermal properties of the hybridized hydrogels were reinforced compared with the neat PNIPAm hydrogel. These results were ascribed to nano-effect created by the hydrophobic POSS-SH nanoparticles. The hybridized hydrogels have potential applications in drug controlled release.     

Assembly and characterization of Ag nanoparticles in PAM-g-PVA/PVP semi-interpenetrating network hydrogels

Polyacrylamide grafted poly(vinyl alcohol)/polyvinylpyrrolidone (PAM-g-PVA/PVP) semi-interpenetrating network (semi-IPN) hydrogels were designed and prepared via a simple free radical polymerization reaction process initiated by a PVA-(NH₄)₂Ce(NO₃)₆ redox system. The structure of the PAM-g-PVA/PVP semi-IPNs was characterized by a Fourier transform infrared spectroscopy. The morphologies of PAM-g-PVA/PVP hydrogels and PAM-g-PVA/PVP/Ag nanocomposite hydrogels were examined by scanning electron microscopy and transmission electron microscopy (TEM). The experimental results indicated that the PAM, PVA or PVP chains can efficiently act as stabilizing agents for Ag nanoparticles. TEM investigation of sample morphology showed the presence of nearly spherical-, square- or rectangular-shaped Ag nanoparticles with diameters ranging from 10 to 60 nm. The characteristic surface plasmon resonance band appeared at 390–400 run as a result of the immobilization of Ag nanoparticles within the hydrogel matrices. The self-assembly of Ag nanoparticles and the swelling behavior of the resulting nanocomposites can be controlled and modulated by altering the mole fraction of PVP in the PAM-g-PVA/PVP semi-IPNs.     

Synthesis and network structure of ionic poly(N,N-dimethylacrylamide-co-acrylamide) hydrogels: Comparison of swelling degree with theory

At four different charge densities, ionic hydrogels based on N,N-dimethylacrylamide (DMAAm), acrylamide (AAm), and itaconic acid (IA) were synthesized by free-radical cross-linking copolymerization in water with N,N-methylenebis(acrylamide) (BAAm) as the cross-linker, ammonium persulfate (APS) as the initiator, and N,N,N′,N′-tetramethylenediamine (TEMED) as the activator. The swelling behaviors of these hydrogels were analyzed in buffer solutions at various pH. It was observed that the swelling behavior of cross-linked ionic poly(N,N-dimethylacrylamide-co-acrylamide) [P(DMAAm-co-AAm)] hydrogels at different pHs agreed with the modified Flory-Rehner equation based both on the phantom network and affine network models and the ideal Donnan theory. In addition, the kinetics of swelling of the hydrogels was studied in pH 2, 5 and 9 buffer solutions. The swelling curves exhibited the characteristic features of transport process, apparently the Fickian diffusion of fast rates.     

Studies on preparation and properties of NIPAAm/hydrophobic monomer copolymeric hydrogels

A series of thermoreversible copolymeric hydrogels with various molar ratios of N-isopropylacrylamide (NIPAAm) and hydrophobic monomers such as 2,2,3,3,4,4,5,5-octafluoropentyl methacrylate (OFPMA) and n-butyl methacrylate (BMA) were prepared by emulsion polymerization. The effect of hydrophobic monomer on the swelling behavior and mechanical properties of the present copolymeric hydrogels was investigated. Results showed that the equilibrium swelling ratio and critical gel transition temperature (CGTT) decreased with an increase of the content of hydrophobic monomer, but the gel strength of the gel increased with an increase of the content of hydrophobic monomer. Due to stronger hydrophobicity of OFPMA, the NIPAAm/OFPMA copolymeric hydrogels had lower swelling ratios and higher gel strengths than NIPAAm/BMA copolymeric gels.     

A novel polyacrylamide nanocomposite hydrogel reinforced with natural chitosan nanofibers

Polyacrylamide (PAM) was used as a matrix material for fabricating novel nanocomposite hydrogels reinforced with natural chitosan nanofibers (CNFs) via in situ free-radical polymerization. The nanocomposite's structure, strength, morphology and rheological properties were investigated. The results showed that the CNFs had a strong interaction with PAM through hydrogen and covalent bondings. The CNFs acted as a multifunctional cross-linker and a reinforcing agent in the hydrogel system. The compression strength and storage modulus of the nanocomposite hydrogels were significantly higher than those of the pure PAM hydrogels and the corresponding PAM/chitosan semi-interpenetrating polymer network (PAM-SIPN) hydrogels. The swelling ratio (SR) of the nanocomposite hydrogels was lower than that of the PAM hydrogel, but was similar to that of the PAM-SIPN hydrogel. Among the CNF contents used, the 1.5 wt% CNF loading level showed the best combined swelling and mechanical properties for the hydrogels.     

Tailoring thermoresponsive nanostructured poly(N-isopropylacrylamide) hydrogels made with poly(acrylamide) nanoparticles

The thermoresponsive behavior and mechanical properties of nanostructured hydrogels, which consist of poly(acrylamide) nanoparticles embedded in a cross-linked poly(N-isopropylacrylamide) hydrogel matrix, are reported here. Nanostructured hydrogels exhibit a tuned volume phase transition temperature (T _VPT), which varies with nanoparticle content in the range from 32 up to 39–40 °C. Moreover, larger equilibrium water uptake, faster swelling and de-swelling rates, and larger equilibrium swelling at 25 °C were obtained with nanostructured hydrogels compared with those of conventional ones. Elastic and Young’s moduli were larger than those of conventional hydrogels at similar swelling ratios. The tuned T _VPT and the de-swelling rate were predicted with a modified Flory–Rehner equation coupled with a mixing rule that considers the contribution of both polymers. These behaviors are explained by a combination of hydrophilic/hydrophobic interactions and by the controlled inhomogeneities (nanoparticles) introduced by the method of synthesis.