Preparation and properties of the novel photoluminescent and thermosensitive hydrogels

Bis[4-(phenyl-isopropyl)phenyl]-4-nitrophenylamine (BiPNPA) (iii) was firstly synthesized via nucleophilic substitution of 4-fluoronitrobenzene (ii) and bis-[4-(phenyl-isopropyl)phenyl]amine (BiPA) (i) in this study, and then compound (iii) was reduced to bis[4-(phenyl-isopropyl)phenyl]-4-aminophenylamine (BiPAmPA) (iv). At last, acrylation of BiPAmPA with acryloyl chloride was performed to obtain a novel bis[4-(phenyl-isopropyl)phenyl]-4-acrylamidophenylamine (BiPAcPA) compound (v). Then, a series of thermosensitive hydrogels were prepared by copolymerization of BiPAcPA and N-isopropyl acrylamide (NIPAAm) by UV irradiation. The effect of BiPAcPA content in the copolymeric hydrogels on the swelling ratio, mechanical properties, and drug release behaviors of the hydrogels was investigated. Results showed that the swelling ratios of the copolymeric hydrogels decreased from 8.2 (g/g) to 5.01 (g/g) when the monomer BiPAcPA content in the copolymeric hydrogel increased from 0.1 mol% to 0.9 mol%. In addition, the thermosensitive behavior obviously decreased with increasing of BiPAcPA content in the hydrogels, but the mechanical properties and crosslinking density of the hydrogel increased with increasing of BiPAcPA content; the caffeine release ratio from 46 % decreased to 29 %. The result of caffeine release also showed that the caffeine-loading amounts decreased with increasing content of BiPAcPA in the hydrogel, but their fractional release increased. In addition, the corresponding copolymers of the copolymeric hydrogels were prepared. Furthermore, the UV absorbance and photoluminescent (PL) behavior of the BiPAcPA, NIPAAm/BiPAcPA copolymeric hydrogels, and their corresponding copolymers in some solvents with different polarities were investigated. The results showed the PL intensity increased with increasing BiPAcPA amounts, especially the wavelength had obvious blue shift phenomenon in THF solvent. The wavelength of UV absorbance and PL emission of BiPAcPA all appeared in visible region. No matter what BiPAcPA monomer, NIPAAm/BiPAcPA hydrogels or NIPAAm/BiPAcPA copolymers, the wavelengths of UV absorbance and PL emission in DMSO solvent are all the same.     

Thermoreversible hydrogels X: Synthesis and swelling behavior of the (N‐isopropylacrylamide‐co‐sodium 2‐acrylamido‐2‐methylpropyl sulfonate) copolymeric hydrogels

A series of thermosensitive hydrogels were prepared from various molar ratios of N‐isopropylacrylamide (NIPAAm) and sodium‐2‐acrylamido‐2‐methylpropyl sulfonate (NaAMPS). Factors such as temperature and initial total monomer concentration and different pH solutions were investigated. Results indicated that the more the NaAMPS content in hydrogel system, the higher the swelling ratio and the gel transition temperature; the higher the initial monomer concentration, the lower the swelling ratio. The result also indicated that the NIPAAm/NaAMPS copolymeric hydrogels had different swelling ratios in various pH environments. The present gels showed a pH‐reversible property between pH 3 and pH 10 and thermoreversibility. The swelling ratios of copolymeric gels were lower in a strong alkaline environment because the gels were screened by counterions. Finally, the drug release behavior of these gels was also investigated in this article. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 1760–1768, 2000     

Thermoreversible hydrogel. XVII. Investigation of the drug release behavior for [N‐isopropylacrylamide‐co‐trimethyl acrylamidopropyl ammonium iodide‐co‐3‐dimethyl (methacryloyloxyethyl) ammonium propane sulfonate] copolymeric hydrogels

A series of copolymeric hydrogels were prepared from various molar ratios of N‐isopropylacrylamide (NIPAAm), trimethyl acrylamidopropyl ammonium iodide (TMAAI), and 3‐dimethyl (methacryloyloxyethyl) ammonium propane sulfonate (DMAPS). Results showed that the swelling ratios of these copolymeric hydrogels increased with an increase of TMAAI content. The drug release behavior of the ionic thermosensitive hydrogels related to their ionicity and drug types. Results indicated that the release ratio of caffeine in the hydrogels was not affected by the ionicity of hydrogels, but increased with increasing of the swelling ratio. The anionic solute (phenol red) strongly interacted with cationic hydrogel (very large K_d), so the phenol red release ratio in cationic gels was very low. On the other hand, CV was adsorbed only on the skin layer of the cationic hydrogel because of the charge repulsion, and released rapidly. Therefore the release ratio was highest for cationic hydrogel to cationic drug. In addition, the partition coefficients (K_d) and the drug delivery behavior of the present gels were also investigated. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 86: 1592–1598, 2002     

Synthesis and swelling behavior of thermosensitive IPN hydrogels based on sodium acrylate and N‐isopropyl acrylamide by a two‐step method

A series of interpenetrating polymer network (IPN) hydrogels having higher swelling ratio (SR) and thermosensitivity were synthesized from sodium acrylate (SA) and N‐isopropyl acrylamide (NIPAAm) by a two‐step method. A series of the porous poly(sodium acrylate ‐co‐1‐vinyl–2‐pyrrolidone) [poly(SA‐co‐VP)], (SV), hydrogels were prepared from acrylic acid having 90% degree of neutralization and VP monomer in the first step. The second step is to immerse the SV dried gels into the NIPAAm solution containing initiator, accelerator, and crosslinker to absorb NIPAAm solution and then polymerized to form the poly(SA‐co‐VP)/poly(NIPAAm) IPN hydrogels (SVN). The effect of the different molar ratios of SA/VP and the content of NIPAAm on the swelling behavior and physical properties of the SVN hydrogels was investigated. Results showed that the SVN hydrogels displayed an obviously thermoreversible behavior when the temperature turns across the critical gel transition temperature (CGTT) of poly(NIPAAm) hydrogel. The pore diameter distributions inside the hydrogel also indicated that the pore sizes inside the SVN hydrogels were smaller than those inside the SV hydrogels. At the same time, the more proportion of SA was added into the hydrogel, the larger pore diameter of the SV hydrogel was formed. The results also showed that the SR decreased with an increase of the VP content in the SV hydrogel and more obviously decreased in the SVN hydrogels. The SVN networks also showed stronger shear moduli than SV hydrogels. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Thermoreversible hydrogels. XIX. Synthesis and swelling behavior and drug release behavior for the N‐isopropylacrylamide/poly(ethylene glycol) methylether acrylate copolymeric hydrogels

A series of thermosensitive copolymeric hydrogels were prepared from various molar ratios of N‐isopropylacrylamide (NIPAAm) and poly(ethylene glycol) methylether acrylate (PEGMEA_n), which was synthesized from acryloyl chloride and poly(ethylene glycol) mono methylether with three oxyethylene chain lengths. Investigation of the effect of the chain length of oxyethylene in PEGMEA_n, and the amount of the PEGMEA_n in the NIPAAm/PEGMEA_n copolymeric gels, on swelling behavior in deionized water was the main purpose of this study. Results showed that the swelling ratio for the present copolymeric gels increased with increasing chain length of oxyethylene in PEGMEA_n and also increased with increase in the amount of PEGMEA_n in the copolymeric gels. However, the gel strength and effective crosslinking density of these gels decreased with increase in swelling ratio. Some kinetic parameters were also evaluated in this study. Finally, the drug release and drug delivery behavior for these gels were also assessed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 1683–1691, 2003     

Thermoreversible hydrogels. IX. Swelling behaviors of thermosensitive hydrogels copolymerized by N‐isopropylacrylamide with 1‐vinyl‐3‐(3‐sulfopropyl) imidazolium betaine

A series of thermosensitive hydrogels were prepared from the various molar ratios of N‐isopropylacrylamide, 1‐vinyl‐3‐(3‐sulfopropyl) imidazolium betaine (VSIB), and N,N′‐methylene‐bis‐acrylamide. The influence of the amount of VSIB in the copolymeric gels on the swelling behaviors in water, in various saline solutions, and at various temperatures was investigated. The results indicated that the higher the VSIB content in the hydrogel system, the higher the swelling ratio and the gel transition temperature. In the saline solution the results showed that when the concentration of salt is higher than the minimum salt concentration (MSC) of poly(VSIB), the deswelling behavior of the copolymeric gel was more effectively suppressed as more VSIB was added to the copolymeric gels. In addition, only the sample containing 12 mol % VSIB (V4) exhibited an antipolyelectrolyte's swelling behavior when the concentration of salt was higher than the MSC of poly(VSIB). This means that the swelling ratio of the hydrogel can be improved with a higher concentration salt solution. In addition, the anion effects were larger than the cation effects in the presence of a common anion (Cl⁻) with different cations and a common cation (K⁺) with different anions for the hydrogel. Finally, the more VSIB in the hydrogel, the higher the diffusion coefficient in dynamic swelling. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 14–23, 2000     

pH‐thermoreversible hydrogels. I. Synthesis and swelling behaviors of the (N‐isopropylacrylamide‐co‐acrylamide‐co‐2‐hydroxyethyl methacrylate) copolymeric hydrogels

A series of pH‐thermoreversible hydrogels that exhibited volume phase transition was synthesized by various molar ratios of N‐isopropylacrylamide (NIPAAm), acrylamide (AAm), and 2‐hydroxyethyl methacrylate (HEMA). The influence of environmental conditions such as temperature and pH value on the swelling behavior of these copolymeric gels was investigated. Results showed that the hydrogels exhibited different equilibrium swelling ratios in different pH solutions. Amide groups could be hydrolyzed to form negatively charged carboxylate ion groups in their hydrophilic polymeric network in response to an external pH variation. The pH sensitivities of these gels also depended on the AAm content in the copolymeric gels; thus the greater the AAm content, the higher the pH sensitivity. These hydrogels, based on a temperature‐sensitive hydrogel, demonstrated a significant change of equilibrium swelling in aqueous media between a highly solvated, swollen gel state and a dehydrated network response to small variations of temperature. pH‐thermoreversible hydrogels were used for a study of the release of a model drug, caffeine, with changes in temperature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 221–231, 1999     

Synthesis and swelling properties of 2‐hydroxyethyl methacrylate‐co‐1‐vinyl‐3‐(3‐sulfopropyl)imidazolium betaine hydrogels

A series of 2‐hydroxyethyl methacrylate/1‐vinyl‐3‐(3‐sulfopropyl)imidazolium betaine (HEMA/VSIB) copolymeric gels were prepared from various molar ratios of HEMA and the zwitterionic monomer VSIB. The influence of the amount of VSIB in copolymeric gels on their swelling behavior in water and various saline solutions at different temperatures and the drug‐release behavior, compression strength, and crosslinking density were investigated. Experimental results indicated that the PHEMA hydrogel and the lower VSIB content (3%) in the HEMA/VSIB gel exhibited an overshooting phenomenon in their dynamic swelling behavior, and the overshooting ratio decreased with increase of the temperature. In the equilibrium water content, the value increased with increase of the VSIB content in HEMA/VSIB hydrogels. In the saline solution, the water content for these gels was not affected by the ion concentration when the salt concentration was lower than the minimum salt concentration (MSC) of poly(VSIB). When the salt concentration was higher than the MSC of poly(VSIB), the deswelling behavior of the copolymeric gel was more effectively suppressed as more VSIB was added to the copolymeric gels. However, the swelling behavior of gels in KI, KBr, NaClO₄, and NaNO₃ solutions at a higher concentration would cause an antipolyelectrolyte phenomenon. Besides, the anion effects were larger than were the cation effects in the presence of a common anion (Cl^?) with different cations and a common cation (K⁺) with different anions for the hydrogel. In drug‐release behavior, the addition of VSIB increased the drug‐release ratio and the release rate. Finally, the addition of VSIB in the hydrogel improved the gel strength and crosslinking density of the gel. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 2888–2900, 2001     

Thermoreversible hydrogels. XV. Swelling behaviors and drug release for thermoreversible hydrogels containing silane monomers

Three series of thermosensitive copolymeric hydrogels were prepared from [3‐(methacryloyloxy)propyl]trimethoxysilane (MPTMOS), [2‐(methacryloyloxy)ethoxy]trimethylsilane (METMS), and (methacryloyloxy)trimethylsilane (MTMS), referred to as the silane monomer, and N‐isopropylacrylamide (NIPAAm) by solution polymerization. The influence of the structures and amounts of silane monomers on the swelling and drug‐released behaviors were studied. The results showed that, because of the hydrophobicity of the silyl group, the more silane monomers in the copolymeric hydrogels the lower was the swelling ratio of the gels. The hydrophobicity of the silyl group affected the swelling mechanism, which resulted from the non‐Fickian diffusion for the gels. The copolymeric gels clearly exhibited gel transition temperatures. The copolymeric hydrogels could be applied to a drug‐release and drug‐delivery system. The delivery amount would approach a steady state after three cycle operations of delivery. The gels also showed an on–off switch behavior on drug release depending on the temperature, and the gels released more CV with the gels in a swollen state. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 2523–2532, 2002     

Thermoreversible hydrogels XI: Effect of salt on the swelling properties of the (n‐isopropylacrylamide‐co‐sodium 2‐acrylamido‐2‐methylpropyl sulfonate) copolymeric hydrogels

The swelling behavior for a series of NIPAAm/NaAMPS copolymeric hydrogels with polyelectrolytic and thermosensitive properties was investigated in various saline solutions. The swelling ratios for the present copolymeric hydrogels were affected by the saline solution, which is the result of the neutralization of the cations in the external solution with the negative charges on the polymeric side chains. The adsorption of aniline by the gels increased when the temperature was higher than the gel transition temperature, and this result showed that, when the gels were in hydrophobic state, the hydrophobic organic molecules were more easily adsorbed onto the gels. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 79: 1675–1684, 2001     

Characterization and caffeine release properties of N‐isopropylacrylamide/hydroxypropyl methacrylate copolymer hydrogel synthesized by gamma radiation

Research efforts have been devoted to demonstrate that the temperature sensitivity characters of poly(N‐isopropylacrylamide)(PNIPAAm) can be applied in the field of drug carriers. A copolymer hydrogel of N‐isopropylacrylamide/hydroxypropyl methacrylate (NIPAAm/HPMA) was synthesized by gamma irradiation. The nature of bonding was characterized by FTIR spectroscopy, whereas the thermal stability was characterized by thermogravimetric analysis (TGA). The influence of NIPAAm/HPMA composition on the swelling properties in water, at different temperatures and different pH values was studied. The release characters of caffeine drug from NIPAAm/HPMA hydrogels were also investigated. The gel fraction of NIPAAm/HPMA was found to increase slightly by increasing the ratio of HPMA in the initial solution. The IR spectra indicate the formation of copolymer hydrogels, whereas the TGA study showed that the NIPAAm/HPMA copolymer hydrogels displayed higher thermal stability than NIPAAm hydrogel. PNIPAAm hydrogel showed higher swelling in water than NIPAAm/HPMA hydrogels. Based on Fick's law, it was demonstrated that the diffusion of water into NIPAAm/HPMA is controlled. It was found that the main parameters affecting the drug release behavior from the hydrogels are composition and pH. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermoreversible hydrogels. VIII. Effect of a zwitterionic monomer on swelling behaviors of thermosensitive hydrogels copolymerized by N‐isopropylacrylamide with N,N′‐dimethyl (acrylamidopropyl) ammonium propane sulfonate

A series of thermosensitive hydrogels were prepared from the various molar ratios of N‐isopropylacrylamide, zwitterionic monomer, N,N′‐dimethyl (acrylamidopropyl) ammonium propane sulfonate (DMAAPS), and N,N′‐methylene‐bis‐acrylamide. The influence of the amount of DMAAPS in the copolymeric gels on the swelling behaviors in water, various saline solutions, and various temperatures was investigated. Results indicated that the higher the DMAAPS content in the hydrogel system, the higher the swelling ratio and the gel transition temperature. In the saline solution results showed that, when the salt concentration was greater than the minimum salt concentration (MSC) of poly(DMAAPS), the deswelling behavior of the N‐isopropylacrylamide gel was suppressed more effectively when more DMAAPS was added into the copolymeric gels; but the swelling ratios of the present copolymeric gels did not significantly change while the salt concentration was lower than the MSC of poly(DMAAPS). In addition, only the sample containing 12 mol % DMAAPS (D4) exhibited an antipolyelectrolyte's swelling behavior when the salt concentration was greater than the MSC of poly(DMAAPS). In other words, only when the amount of DMAAPS added into the gel is over some proportion, can the hydrogel show an antipolyelectrolyte's swelling behavior in concentrated salt solution. In saline solutions, the anion effects were greater than the cation effects in the presence of common anion (Cl⁻) with different cations and common cation (K⁺) with different cations for these gels. Finally, the more DMAAPS content in the hydrogel, the higher the diffusion coefficient in dynamic swelling. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 2170–2180, 1999     

Swelling and drug‐release behavior of the poly(AA‐co‐N‐vinyl pyrrolidone)/chitosan interpenetrating polymer network hydrogels

A series of novel hydrogels were prepared from acrylic acid (AA), N‐vinyl pyrrolidone (NVP), and chitosan by photopolymerization. The swelling behavior, gel strength, and drug release behavior of the poly(AA/NVP) copolymeric hydrogels and corresponding interpenetrating polymer network hydrogels were investigated. Results showed that the swelling ratios for the present hydrogels decreased with an increase of NVP content in the gel, but the gel strength increased with an increase of NVP content in the gel. Results also showed that the drug‐release behavior for the gels is related to the ionicity of drug and the swelling ratio of the gel. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2135–2142, 2004     

Thermo‐responsive injectable hydrogel system based on poly(N‐isopropylacrylamide‐co‐vinylphosphonic acid). I. Biomineralization and protein delivery

To achieve the injectable hydrogel system in order to improve bone regeneration by locally delivering a protein drug including bone morphogenetic proteins, thermo‐responsive injectable hydrogels composed of N‐isopropylacrylamide (NIPAAm) and vinyl phosphonic acid (VPAc) were prepared. The P(NIPAAm‐co‐VPAc) hydrogels were also biomineralized by urea‐mediation method to create functional polymer hydrogels that deliver the protein drug and mimic the bone extracellular matrix. The loosely cross‐linked P(NIPAAm‐co‐VPAc) hydrogels were pliable and fluid‐like at room temperature and could be injected through a small‐diameter aperture. The lower critical solution temperature (LCST) of P(NIPAAm‐co‐VPAc) hydrogel was influenced by the monomer ratio of NIPAAm/VPAc and the hydrogel with a 96/4 molar ratio of NIPAAm/VPAc exhibited an LCST of ～34.5°C. Water content was influenced by temperature, NIPAAm/VPAc monomer ratio, and biomineralization; however, all hydrogels maintained more than about 77% of the water content even at 37°C. In a cytotoxicity study, the P(NIPAAm‐co‐VPAc) and biomineralized P(NIPAAm‐co‐VPAc) hydrogels did not significantly affect cell viability. The loading content of bovine serum albumin in hydrogel, which was used as a model drug, gradually increased with the amount of VPAc in the hydrogel owing to the ionic interaction between VPAc groups and BSA molecules. In addition, the release behavior of BSA from the P(NIPAAm‐co‐VPAc) hydrogels was mainly influenced by the drug loading content, water content, and biomineralization of the hydrogels. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Preparation of alginate/poly(N‐isopropylacrylamide) semi‐interpenetrating and fully interpenetrating polymer network hydrogels with γ‐ray irradiation and their swelling behaviors

Semi‐interpenetrating polymer network (semi‐IPN) and fully interpenetrating polymer network (full‐IPN) hydrogels composed of alginate and poly(N‐isopropylacrylamide) were prepared with γ‐ray irradiation. The semi‐IPN hydrogels were prepared through the irradiation of a mixed solution composed of alginate and N‐isopropylacrylamide (NIPAAm) monomer to simultaneously achieve the polymerization and self‐crosslinking of NIPAAm. The full‐IPN hydrogels were formed through the immersion of the semi‐IPN film in a calcium‐ion solution. The results for the swelling and deswelling behaviors showed that the swelling ratio of semi‐IPN hydrogels was higher than that of full‐IPN hydrogels. A semi‐IPN hydrogel containing more alginate exhibited relatively rapid swelling and deswelling rates, whereas a full‐IPN hydrogel showed an adverse tendency. All the hydrogels with NIPAAm exhibited a change in the swelling ratio around 30–40°C, and full‐IPN hydrogels showed more sensitive and reversible behavior than semi‐IPN hydrogels under a stepwise stimulus. In addition, the swelling ratio of the hydrogels continuously increased with the pH values, and the swelling processes were proven to be repeatable with pH changes. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4439–4446, 2006     

Thermosensitive Poly(N-isopropylacrylamide-co-acrylonitrile) Hydrogels with Rapid Response

Acrylonitrile （AN） was copolymerized with N-isopropylacrylamide （NIPA） to synthesize thermosensitive hydrogels, and the on-off switch behavior of poly（NIPA-co-AN） hydrogels with different fraction of hydrophobic component （AN） was investigated. It is found that the lower critical solution temperature （LCST）, the swelling ratio at certain temperature and the reswelling rate of poly（NIPA-co-AN） hydrogels decreased as AN unit fraction in copolymers increased. In order to improve the responsive rate of poly（NIPA-co-AN） hydrogels, they were further treated by surface crosslinking using N, N′-methylene bisacrylamide （BIS） as a crosslinking agent. The swelling and deswelling behaviors of these copolymers were compared with those of the untreated hydrogels. The results indicated that the responsive rate of poly（NIPA-co-AN） hydrogel was improved by surface crosslinking. The resulting hydrogels bearing cyano groups with fast response have potential applications in the field of drug-controlled release and immobilization of biomolecules.     

Effect of montmorillonite on the swelling behavior and drug‐release behavior of nanocomposite hydrogels

A series of nanocomposite hydrogels were prepared from various ratios of N‐isopropylacrylamide (NIPAAm) and organic montmorillonite (MMT). The influence of the extent of MMT in the NIPAAm/MMT nanocomposite hydrogels on the physical properties and drug‐release behavior was the main purpose of this study. The microstructure and morphology were identified by X‐ray diffraction (XRD) and scanning electronic microscopy (SEM). The results showed that the swelling ratios for these nanocomposite hydrogels decreased with increase in the content of MMT. The gel strength and Young's modulus of the gels also increased with increase in the content of MMT. XRD results indicated that the exfoliation of MMT was achieved in the swollen state. Finally, the drug‐release behavior for the gels was also assessed. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3652–3660, 2003     

pH/thermoreversible hydrogels III: Synthesis and swelling behaviors of (N-isopropylacrylamide-co-acrylic acid) copolymeric hydrogels

A series of pH-thermoreversible hydrogels exhibiting volume phase transition were synthesized by three degrees of neutralization (DN) of acrylic acid (AA) and N-isopropylacrylamide (NIPAAm). The influence of environmental conditions, such as temperature and pH, on the swelling behavior of these copolymeric gels is investigated in this article. Results show that the negatively charged hydrogels exhibit different equilibrium swelling ratios at different pH values depending on the ionic composition. The pH-sensitivities of these gels also strongly depend on the DN of AA in the copolymeric gels. The results show that the higher the DN, the higher the gel pH-sensitivity. These hydrogels based on a temperature-sensitive hydrogel demonstrate a larger change of equilibrium swelling in aqueous media between a highly solvated, swollen gel state and a collapsed dehydrated network in response to a variation of temperature. On the other hand, a significant phenomenon that was found in the gel swelling kinetics was an overshooting under high temperature conditions. The presented hydrogels were used for release of model drugs that occur at the changes of surrounding conditions, such as temperature and pH, in this study. It was also found that the higher the DN of AA, the higher the gel transition temperature and the larger the release in a high temperature environment and, at the same time, the larger the swelling ratios.     

Thermosensitive and ampholytic hydrogels for salt solution

A series of N‐isopropylacrylamide/[[3‐(methacryloylamino)propyl]dimethy(3‐sulfopropyl)ammonium hydroxide] (NIPAAm/MPSA) copolymer hydrogels were prepared with various compositions. Swelling of the hydrogels in water, aqueous NaCl, KCl, CaCl₂, and MgCl₂ solutions was studied. NIPAAm/MPSA hydrogels have a higher degree of swelling in water and salt solutions than that of poly(N‐isopropylacrylamide) (PNIPAAm). Also, NIPAAm/MPSA hydrogels are more salt resistant when deswelling in salt solutions. For <7 mol % MPSA, the formed hydrogels retain both temperature reversibility and high swelling. A higher content of MPSA (>11 mol %) leads to better salt resistance but a decrease in thermosensitivity. The swelling of NIPAAm/MPSA hydrogel in 0.05M NaCl is non‐Fickian. In NaCl and KCl aqueous solutions, the zwitterionic hydrogels do not show obvious antipolyelectrolyte swelling behavior, whereas in divalent salt CaCl₂ and MgCl₂ solutions, the swelling ability of NIPAAm/MPSA hydrogels is enhanced at low salt concentration, then decreases with further increase in salt concentration. The lower critical solution temperatures of NIPAAm/MPSA hydrogels are also affected by concentrated salt solution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2032–2037, 2003     

Thermoreversible hydrogels VI: Swelling behavior of the (N-isopropylacrylamide-co-diethyl methyl methacryloyloxyethyl ammonium iodide) copolymeric hydrogels in aqueous salt solutions

A series of N-isopropylacrylamide/diethyl methyl methacryloyloxyethyl ammonium iodide (NIPAAm/DEMMAI) copolymeric gels were prepared from blending NIPAAm, cationic monomer DEMMAI, and N,N′-methylene bisacrylamide (NMBA) in various molar ratios in this article. The effects of the amount of the cationic monomer in the copolymeric gels on the swelling behaviors in water and various saline solutions at various temperatures were investigated. Results showed that the swelling ratios of copolymeric gels were significantly larger than those of pure NIPAAm gel, and that the more the DEMMAI content, the higher the gel transition temperature. In the saline solution, results showed that the swelling ratio for pure NIPAAm gel had not changed significantly with an increase of the salt concentration until the salt concentration was larger than 0.1 M. The swelling ratios for the copolymeric gels NIPAAm/DEMMAI were decreased with increasing salt concentration. In various saline solutions, results showed that the anionic effects were greater than cationic effects in the presence of common anion with different cations and common cation with different anions for these hydrogels. Finally, we also tested the reversibility of the NIPAAm/DEMMAI copolymeric gels. The deswelling and reswelling kinetics were dependent on the temperature which was below or above the gel transition temperature. The gel with a small DEMMAI content has a good reversibility.