Synthesis of dual pH- and temperature-sensitive poly(N-isopropylacrylamide-co-acrylic acid)/sewage sludge ash hydrogel with the simultaneously high performance of swelling and deswelling

An advanced dual pH- and temperature-sensitive hydrogel (NASH2.5) was optimally synthesized through modification of N-isopropylacrylamide (NIPAM) hydrogel with introducing 5 mol% acrylic acid (AA) and 2.5 wt% sewage sludge ash (SSA). The swelling kinetic results showed that NASH2.5 exhibited both high equilibrium swelling ratio and swelling rate, which was attributed to the higher porous structure as shown in scanning electron microscope, and the more hydrogen bonding formed inside of the hydrogel as investigated in Fourier transform infrared spectrometer. In addition, its curve was better fitted to the pseudo-second-order model, indicating that the water absorption process was dominated by chemisorption through forming the hydrogen bonding among the water molecules and carboxyl/silanol groups of the hydrogel. Compared with the pure NIPAM hydrogel, the water transport mechanism switched from Case I diffusion to Case II diffusion by introduction of AA and further SSA. Furthermore, through the results of the deswelling kinetics in pH value change (from 9 to 4 and 2, respectively), temperature value change (from 25 to 40, 50, and 60°C, respectively), and dual pH and temperature values changes, NASH2.5 not only presented a high pH sensitivity, but also showed high sensitive to temperature by achieving high water recovery ratio in rapid dehydrated rate. Therefore, the dual stimuli-sensitive hydrogel with the simultaneously high performance of swelling and deswelling would provide a suitable alternative for specific applications such as pollutant adsorption.     

Preparation and characterization of temperature- and pH-sensitive hemicellulose-containing hydrogels

In this work, a hemicellulose-containing hydrogel was synthesized. As the first step, a temperature- and pH-sensitive copolymer was synthesized from itaconic acid and N-isopropylacrylamide (NIPAAm). Then the hydrogel was prepared by reacting the copolymer with acylated hemicellulose and polyvinyl alcohol. The morphology, compressive strength, thermal stability, swelling/deswelling behavior, drug-release behavior performances of the hydrogels were investigated. The lower critical solution temperature of the hydrogels varied in 34–44°C when the NIPAAm and itaconic acid mass ratios ranged in 100/0–90/10. Both temperature and pH had a significant influence on equilibrium swelling ratio of hydrogels. The equilibrium swelling ratio increased with pH, but decreased with temperature. Cytocompatibility assay demonstrated that this hemicellulose-containing hydrogel was biocompatible. The release process of salicylic acid suggested that this hydrogel had a potential use in controlled drug release.     

A study on the deswelling behaviour of a thermo-responsive hydrogel prepared by radiation polymerization

A new kind of thermo-responsive hydrogel, poly(methacryloyl-DL-alanie methyl ester), was synthesized by means of radiation polymerization. The swelling and deswelling were reversible. The deswelling kinetics changes with the variation of temperature. It was found that a rigid membrane was formed during deswelling at 40°C. In the case of deswelling at 20°C, no skin was found. The hydrogel deswelled uniformly.     

Preparation and separation function of N‐isopropylacrylamide copolymer hydrogels

In this paper, N‐isopropylacrylamide (NIPA) was synthesized by acrylonitrile and isopropanol. Poly(N‐isopropylacrylamide) (PNIPA) was prepared by a chemical method. The dependence of its swelling behavior on temperature was studied. Results showed that PNIPA hydrogel was a temperature‐sensitive gel. Its LCST (lower critical solution temperature) was about 32 °C, and its swelling ratio (at 20 °C) was about 17–18. Sodium acrylate (SA) and sodium methylacrylate (SMA) were copolymerized with NIPA respectively. Equilibrium swelling ratios of the copolymer hydrogels at lower temperature were two to three times that of PNIPA. The LCST of the copolymer hydrogels could be controlled between 32 and 45 °C by adjusting the content of SA or SMA. Kinetics of P(NIPA‐co‐SA) hydrogels, whether swelling or shrinking processes, were in good agreement with apparent second order kinetic equations. Several experiments were designed to separate aqueous bovine serum albumin solution using the hydrogels prepared above. The separation efficiency was about 80%. Copyright © 2000 John Wiley & Sons, Ltd.     

Thermoresponsive properties of porous poly(N‐isopropylacrylamide) hydrogels prepared in the presence of nanosized silica particles and subsequent acid treatment

Porous poly(N‐isopropylacrylamide) hydrogels were prepared by the free‐radical polymerization of its monomer and a suitable crosslinker in the presence of spherical silica particles of different sizes (74 and 1600 nm) and by the subsequent acid extraction of silica. The yields were 81–83%, and the yields were not affected by the silica content. Scanning electron microscopy observations revealed the porous structure of the hydrogels. Porous and nonporous hydrogels showed volume phase transitions from swelling states to deswelling states at approximately 30 °C, as analyzed by the ratio of the diameter of cylinder‐shaped hydrogels to that of the glass tube used for the hydrogel preparation at the corresponding temperature. Deswelling, which was analyzed by rapid changes in the temperature of the aqueous media from 20 to 40 °C, was facilitated by decreased silica particle size and increased silica content. The deswelling rate constant of the hydrogel prepared with 74‐nm silica at 10 v/v % (silica/solvent) was more than 1500 times greater than that of conventional hydrogels. Swelling was similarly analyzed through changes in the temperature from 40 to 20 °C and was independent of the pore structure. The deswelling–swelling cycle was repeatable with reasonable reproducibility. Moreover, the mechanical strength of the porous hydrogels was significantly maintained compared with that of conventional nonporous hydrogels. This method produced thermoresponsive hydrogels of suitable mechanical strength and remarkable deswelling properties. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 4228–4235, 2002     

Effect of Pore-Forming Agent Type on Swelling Properties of Macroporous Poly(N-[3-(dimethylaminopropyl)]-methacrylamide-co-acrylamide) Hydrogels

Macroporous poly(N-[3-(dimethylaminopropyl)]methacrylamide-co-acrylamide) [P(DMAPMA-co-AAm)] hydrogels were prepared by free-radical crosslinking copolymerization of corresponding monomers in water using two different pore-forming agents such as hydroxypropyl celluose (HPC) and poly(ethylene glycol) (PEG). The effect of these pore-forming agents on the volume phase transition temperature (VPT-T), interior morphology and swelling/deswelling kinetics of the P(DMAPMA-co-AAm) hydrogels was investigated. Scanning electron micrographs revealed that the interior network structure of the hydrogel matrix became more porous due to the presence of HPC or PEG pore-forming agents. The more porous matrix provided numerous water channels for water diffusion in or out of the matrix and, therefore, an improved response rate to the external stimuli. Particularly, due to its unique macroporous structure, the PEG-modified hydrogel showed a tremendously faster response to the external temperature changes during deswelling process and the swelling process at 22°C.     

Rapid swelling and deswelling in cryogels of crosslinked poly(N-isopropylacrylamide-co-acrylic acid)

Thermally sensitive hydrogels of poly[N-isopropylacrylamide (NIPA)-co-acrylic acid (AA)] hydrogels with N,N-methylene bisacrylamide (BIS) as crosslinker have been synthesized via a two-step procedure in which, the initial polymerisation is conducted for various times at 18 °C, this step being followed by polymerisation for one fixed time at −22 °C. The gravimetrically determined rates of swelling/deswelling for these materials termed “cryogels” prepared by this two-step polymerisation are much higher than those for the same type of hydrogel prepared via conventional methods (30 °C for 24 h). For example the time for the former xerogel to take up 70% of its final water content at 25 °C is just 18 min, compared with a time 300 min for the latter to attain the same uptake of water. During deswelling (shrinking) at 50 °C, which is above the lower critical temperature, the hydrogel loses 60 and 90 wt% water in 1 and 10 min respectively, compared to a timescale for the corresponding crosslinked copolymers prepared by conventional methods of about 100 min for 50 wt% water loss. A third type of hydrogel was made by a cold treatment (CT), for which the hydrogel prepared by conventional polymerization was stored in the frozen state. The swelling rate of these CT xerogels was the same as that for xerogels prepared by conventional polymerization, but the deswelling rate of the former was higher than that of the latter; for example, during deswelling, a loss of 90% water is attained within a few minutes.Scanning electron microscopy, digital photographs and flotation experiments together with swelling ratio studies reveal that the polymeric network of cryogel produced by the two-step polymerization method is characterized by an open structure with more pores and higher swelling ratio but lower mechanical strength compared to the conventional hydrogels. Such rapid response hydrogels have potential applications in separation and drug release technologies for example.     

Rapid swelling and deswelling in cryogels of crosslinked poly(N-isopropylacrylamide-co-acrylic)

Thermally sensitive hydrogels of poly[N-isopropylacrylamide (NIPA)-co-acrylic(AA)] hydrogels with N,N-methylene bisacrylamide (BIS) as crosslinker have been synthesised via a two-step procedure in which, the initial polymerisation is conducted for various times at 18 °C, this step being followed by polymerisation for one fixed time at −22 °C. The gravimetrically determined rates of swelling/deswelling for these materials termed “cryogels” prepared by this two-step polymerisation are much higher than those for the same type of hydrogel prepared via conventional methods (30 °C for 24 h). For example the time for the former xerogel to take up 70% of its final water content at 25 °C is just 18 min, compared with a time 300 min for the latter to attain the same uptake of water. During deswelling (shrinking) at 50 °C, which is above the lower critical temperature, the hydrogel loses 60 and 90 wt.% water in 1 and 10 min respectively, compared to a timescale for the corresponding crosslinked copolymers prepared by conventional methods of about 100 min for 50 wt.% water loss. A third type of hydrogel was made by a cold treatment (CT), for which the hydrogel prepared by conventional polymerisation was stored in the frozen state. The swelling rate of these CT xerogels was the same as that for xerogels prepared by conventional polymerisation, but the deswelling rate of the former was higher than that of the latter; for example, during deswelling, a loss of 90% water is attained within a few minutes.Scanning electron microscopy, digital photographs and flotation experiments together with swelling ratio studies reveal that the polymeric network of cryogel produced by the two-step polymerisation method is characterised by an open structure with more pores and higher swelling ratio but lower mechanical strength compared to the conventional hydrogels. The polymerisation was taking place on moderate freezing condition and the hydrogel was stored in a frozen state and subsequent thawing of polymer to be very useful the acceleration the response rate of this kind hydrogels. Such rapid response hydrogels have potential applications in separation and drug release technologies for example.     

Novel salep‐based chelating hydrogel for heavy metal removal from aqueous solutions

A novel optimized chelating hydrogel was synthesized via graft copolymerization of acrylamide and 2‐hydroxyethyl methacrylate (as two‐dentate chelating co‐monomer) onto salep (a multicomponent polysaccharide obtained from dried tubers of certain natural terrestrial orchids) using N,N′‐methylenebisacrylamide as a crosslinker and ammonium persulfate as an initiator. Reaction parameters (N,N′‐methylenebisacrylamide and ammonium persulfate amounts as well as acrylamide/2‐hydroxyethyl methacrylate weight ratio) affecting the water absorption of the chelating hydrogel were optimized using a systematic method to achieve a hydrogel with high swelling capacity as possible. Heavy metal ion adsorption capacity of the optimized hydrogel for metal ions [Cu (II), Pb (II), Cd (II), and Cr (III)] were investigated in aqueous media containing different concentrations of these ions (5–50 ppm). The results showed that the hydrogel have great potential for heavy metal removal from aqueous solutions. The hydrogel formation was confirmed by Fourier transform infrared spectroscopy, and surface morphology study of the hydrogel was performed by scanning electron microscope. Copyright © 2016 John Wiley & Sons, Ltd.     

快速响应的温敏性聚(N-异丙基丙烯酰胺)水凝胶的合成及表征

快速响应的温敏性聚(N-异丙基丙烯酰胺)水凝胶的合成及表征;N-异丙基丙烯酰胺;水凝胶;温敏性;快速响应     

Preparation and characterization of a novel IPN hydrogel memberane of poly(N-isopropylacrylamide)/carboxymethyl chitosan (PNIPAAM/CMCS)

A novel type of interpenetrating polymer networks (IPN) hydrogel membrane of poly(N-isopropylacrylamide)/carboxymethyl chitosan (PNIPAAm)/(CMCS) was prepared, and the effects of the feed ratio of components, swelling medium and irradiation dose on the swelling and deswelling properties of the hydrogel was systematically studied. The results showed that the introduction of CMCS did not shift the LCST (at 32 °C), which is similar to the pure PNIPAAm. The lowest swelling ratio was at pH 2. There was little influence of irradiation dose on the thermo- and pH-sensitivity of the IPN hydrogel, increasing dose only decreased the swelling ratio. The PNIPAAm:CMCS=1:4 w/w hydrogel was not thermo-sensitive in distilled water, whereas it showed a discontinuous volume phase transition in pH 2 and a continuous one in pH 8 buffer. Consequently, a combination of pH and temperature can be coupled to control the responsive behavior of these hydrogels.     

Preparation and release profiles of pH/temperature-responsive carboxymethyl chitosan/P(2-(dimethylamino) ethyl methacrylate) semi-IPN amphoteric hydrogel

Thermo- and pH-responsive semi-IPN polyampholyte hydrogels were prepared by using carboxymethyl chitosan and P(2-(dimethylamino) ethyl methacrylate) with N N'-Methylenebisacrylamide (BIS) as crosslinking agent. It was found that the semi-IPN hydrogel shrunk most at the isoelectric point (IEP) and swelled when pH deviated from the IEP. Its swelling ratio dramatically decreased between 30 and 50 °C at pH 6.8 buffer solution. It also showed good reversibility. The UV results showed that when the pH values of drug release medium were 3.7, 6.8, and 9 at 25 °C, the cumulative release rates reached 83.1, 51.5, and 72.2%, respectively. The release rate of coenzyme A (CoA) was higher at 50 °C than 37 and 25 °C at pH 6.8 solution. The release rate decreased with increasing the content of carboxymethyl chitosan at 25 °C in pH 6.8 solution. The results showed that semi-IPN hydrogel seems to be of great promise in pH/temperature drug delivery systems.     

A novel method to prepare temperature/pH‐sensitive poly(N,N‐diethylacrylamide‐co‐acrylic acid) hydrogels with rapid swelling/deswelling behaviors

Fast responsive temperature‐ and pH‐sensitive hydrogels of poly(N,N‐diethylacrylamide‐co‐acrylic acid) (P(DEA‐co‐AA)) have been synthesized successfully by a two‐step procedure, in which the initial polymerization was conducted at constant temperature for 15 min, followed by further polymerization at ?30°C for 12 hr. Swelling studies showed that hydrogels thus prepared had almost the same temperature and pH sensitivity compared with the conventional ones (polymerized at 24°C for 12 hr). However, hydrogels thus prepared had faster swelling/deswelling rates in distilled water than the conventional ones, and their deswelling rates in low pH buffer solutions were also faster than the conventional ones. These improved properties were attributed to the porous network structure, which was confirmed by the results of scanning electron microscopy. Copyright © 2009 John Wiley & Sons, Ltd.     

Biocompatible hydrogel for cartilage repair with adjustable properties

Synthesis of hydrogel at mild conditions is considered one most important challenge, especially if the hydrogel will be used for hosting bioactive materials or drugs. The procedure of hydrogel preparation should have no effect on the properties of the hosted materials. Hyaluronic acid (HA) was modified by adding dialdehyde groups to its structure to facilitate formation of hydrogel at very mild conditions. Dialdehyde HA (DHA) was prepared through oxidation of HA using sodium metaperiodate as oxidizing agent. The prepared DHA was characterized by Fourier‐transform infrared (FTIR) spectroscopy and X‐ray diffraction (XRD) and aldehyde content. A hydrogel was prepared using different chitosan/DHA molar ratio and fixed amount of glutaraldehyde at 25°C. The prepared hydrogel has tunable properties and pores size depending on the chitosan/DHA molar ratio. Sodium diclofenac was loaded on the hydrogel as a model drug. The hydrogel was characterized by FTIR spectroscopy, swelling rate, gel fraction, drug release profile, and cytotoxicity. The results obtained indicated that the properties of the prepared hydrogel, including gelling time, gel fraction, swelling, pores size, and drug release profile are highly tuned depending on the chitosan/DHA molar ratio. The drug loading efficiency was in the range of 70% to 85%. The cytotoxicity results reveal that the prepared hydrogel has a very low toxicity in presence and absence of sodium diclofenac.     

Synthesis and characterization of PVP/AAc copolymer hydrogel and its applications in the removal of heavy metals from aqueous solution

Chelating poly(vinylpyrrolidone/acrylic acid) (PVP/AAc) copolymer hydrogels were prepared by radiation-induced copolymerization. The effects of preparation parameters such as PVP content in the hydrogel and irradiation dose on the swelling behavior of the hydrogel were studied. The pH dependent swelling was investigated. The thermal stability of the prepared hydrogel and the metal chelated ones was characterized by TGA. The removal of Fe(III), Cu(II), and Mn(II) from aqueous solution by the prepared PVP/AAc chelating hydrogel was examined by batch equilibration technique. The influence of treatment time, pH, and the initial feed concentration on the amount of the metal ions removed was studied. The results show that the removal of the metal ion followed the following order: Fe(III) > Cu(II) > Mn(II). The amounts of the removed metal ions increased with treatment time and pH of the medium. To re-use the hydrogel, the metal ions were stripped by using 2 N HCl.     

Synthesis and characterization of thermo-sensitive poly (N-isopropylacrylamide) hydrogel with fast response rate

Thermo-sensitive poly (N-isopropylacrylamide) (PNIPA) hydrogel with fast response rate was prepared by polymerizing N-isopropylacrylamide (NIPA) in an aqueous hydroxyl-propyl-methyl cellulose solution. The volume phase transition temperature of PNIPA hydrogels was characterized by differential scanning calorimetry (DSC), and the surface morphology was observed by scanning electron microscopy (SEM). The swelling ratios of the hydrogels at different temperatures were measured. Furthermore, the deswelling kinetics of the hydrogels was also studied by measuring their water retention capacity. In comparison with a conventional PNIPA hydrogel prepared in water, the hydrogel synthesized in aqueous hydroxyl-propyl-methyl cellulose solution has higher swelling ratios at temperatures below the lower critical solution temperature and exhibits a much faster response rate to temperature changes. For example, the hydrogel made in aqueous hydroxyl-propyl-methyl cellulose solution lost 89% water within 1 min and about 93% water in 4 min, whereas the conventional hydrogel lost only about 66% water in 15 min from the deswelling measurement in similar conditions. Translated from Chinese Journal of Applied Chemistry, 2006, 23(6): 581–585 (in Chinese)     

Polymer Supported Schiff Base Complexes of Iron(III), Cobalt(II) and Nickel(II) Ions and their Catalytic Activity in Oxidation of Phenol and Cyclohexene

The polymer supported transition metal complexes of N,N′‐bis (o‐hydroxy acetophenone) hydrazine (HPHZ) Schiff base were prepared by immobilization of N,N′‐bis(4‐amino‐o‐hydroxyacetophenone)hydrazine (AHPHZ) Schiff base on chloromethylated polystyrene beads of a constant degree of crosslinking and then loading iron(III), cobalt(II) and nickel(II) ions in methanol. The complexation of polymer anchored HPHZ Schiff base with iron(III), cobalt(II) and nickel(II) ions was 83.30%, 84.20% and 87.80%, respectively, whereas with unsupported HPHZ Schiff base, the complexation of these metal ions was 80.3%, 79.90% and 85.63%. The unsupported and polymer supported metal complexes were characterized for their structures using I.R, UV and elemental analysis. The iron(III) complexes of HPHZ Schiff base were octahedral in geometry, whereas cobalt(II) and nickel(II) complexes showed square planar structures as supported by UV and magnetic measurements. The thermogravimetric analysis (TGA) of HPHZ Schiff base and its metal complexes was used to analyze the variation in thermal stability of HPHZ Schiff base on complexation with metal ions. The HPHZ Schiff base showed a weight loss of 58% at 500°C, but its iron(III), cobalt(II) and nickel(II) ions complexes have shown a weight loss of 30%, 52% and 45% at same temperature. The catalytic activity of metal complexes was tested by studying the oxidation of phenol and epoxidation of cyclohexene in presence of hydrogen peroxide as an oxidant. The supported HPHZ Schiff base complexes of iron(III) ions showed 64.0% conversion for phenol and 81.3% conversion for cyclohexene at a molar ratio of 1∶1∶1 of substrate to catalyst and hydrogen peroxide, but unsupported complexes of iron(III) ions showed 55.5% conversion for phenol and 66.4% conversion for cyclohexene at 1∶1∶1 molar ratio of substrate to catalyst and hydrogen peroxide. The product selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was 90.5% and 96.5% with supported HPHZ Schiff base complexes of iron(III) ions, but was found to be low with cobalt(II) and nickel(II) ions complexes of Schiff base. The selectivity for catechol (CTL) and epoxy cyclohexane (ECH) was different with studied metal ions and varied with molar ratio of metal ions in the reaction mixture. The selectivity was constant on varying the molar ratio of hydrogen peroxide and substrate. The energy of activation for epoxidation of cyclohexene and phenol conversion in presence of polymer supported HPHZ Schiff base complexes of iron(III) ions was 8.9 kJ mol^?1 and 22.8 kJ mol^?1, respectively, but was high with Schiff base complexes of cobalt(II) and nickel(II) ions and with unsupported Schiff base complexes.     

Preparation of thermally sensitive poly[N-isopropylacrylamide-co-(maleic acid)] hydrogel membrane by electrospinning using a green solvent

Poly[N-isopropylacrylamide-co-(maleic acid)], poly(NIPA-co-MA), was synthesized by radical polymerization in an aqueous solution composing of 35% mol N-isopropylacrylamide/maleic acid. Poly(NIPA-co-MA) hydrogel nanofibrous membrane was fabricated by electrospinning using ethanol as solvent. The electrospun nanofibers were cross-linked using diethylene glycol as cross-linker, followed by a heat-induced esterification reaction at 145°C. The average diameter of electrospun fibers was 117 ± 33 nm. The hydrogel membrane exhibited a temperature sensitive property. Its minimum and maximum water absorption ratios were 4 ± 0 g g^?1 at 50°C and 17 ± 4 g g^?1 at 34°C, respectively. An equilibrium swelling state of the electrospun membrane was reached within 5 min.     

Investigation of the swelling behavior of hydrogels derived from high-molecular-weight poly(2-ethyl-2-oxazoline)

Thermoresponsive hydrogels are of great importance as smart materials. They are usually composed of cross-linked polymers with a lower critical solution temperature (LCST). Although much is known about networks of poly(N-isopropylacrylamide), all other polymers are somewhat neglected. In this work, the temperature-dependent swelling behavior of differently cross-linked thermoresponsive poly(2-ethyl-2-oxazoline) (PEtOx) hydrogels were investigated with regard to varying parameters of the network composition. It was found that the degrees of swelling of the hydrogels converge for a certain polymer/solvent system at a distinct temperature independent of its degree of cross-linking. Furthermore, this temperature correlates with the LCST of the respective starting PEtOx. Its net chain molecular weight M_c only affects the maximum degree of swelling and thus, the swelling–deswelling rate of the hydrogel. The fundamental structure/property relations found in this study could be useful to predict the behavior of other thermoresponsive hydrogels.     

Synthesis and characteristic of the thermo- and pH-sensitive hydrogel and microporous hydrogel induced by the NP-10 aqueous two-phase system

A series of novel thermo- and pH-sensitive (NP10-AA TPS) hydrogels and microporous (NP10-AA MP) hydrogels, inducing by polyoxyethylene (10) nonyl phenyl ether (NP-10) aqueous two-phase system, was designed and fabricated with acrylic acid (AA) as the monomer for the first time. The resultant NP10-AA TPS hydrogel, compared with the traditional TPS hydrogel, was more advanced in both of the high swelling ratio and the variable lower critical solution temperature (LCST). A simple synthesis technique of the NP10-AA MP hydrogel was developed. The thermo-sensitivity of the NP10-AA TPS hydrogel including the initial swelling ratio, LCST, dehydrated efficiency, was depended strongly on the crosslinker (MBA), initiator (APS), NP-10 and AA concentration. The swelling rate of the NP10-AA MP hydrogel was much higher than that of AA hydrogel dehydrated in the same lyophilization condition.