Effect of poly(ethylene glycol)-derived crosslinkers on the properties of thermosensitive hydrogels

Three crosslinkers, poly(ethylene glycol) diacrylate (PEGDA), glycerol ethoxylate triacrylate (GETA) and citric acid-(PEG acrylate)₃ (CA-PEGTA) derived from poly(ethylene glycol) (PEG) were synthesized at first. The three series of poly (N-isopropylacrylamide) (PNIPAAm) hydrogels were prepared by photopolymerization with the crosslinkers and compared with a hydrogel based on commercial crosslinker, N,N′-methylene bis-acrylamide (NMBA). The influence of the crosslinker structures and contents on the swelling behaviour, mechanical properties, and drug release of the hydrogels was investigated. The results showed that the hydrogels based on PEGDA and NMBA exhibited the highest and the lowest swelling ratio, respectively. The content of crosslinker of all hydrogel series showed good thermosensitivity and thermo-reversibility. The critical gel transition temperature (CGTT) appeared at 32 °C for the hydrogel based on NMBA, but appeared at about 34 °C for other hydrogels due to higher hydrophilicity of the crosslinker. In the mechanical properties, three-arms crosslinker GETA and CA-PEGTA led to higher mechanical strength than a linear crosslinker PEGDA. A hydrogel based on GETA (NG6) showed the highest shear modulus of 656.9 kPa and Young’s modulus of 1655.0 kPa. The hydrogels containing higher content of crosslinker revealed lower swelling ratio and higher mechanical strength. In the drug release, the hydrogels with higher swelling ratios showed higher drug absorbed. The highest release percentage of caffeine and vitamin B12 for hydrogel based on PEGDA (NP6) could reach 68.3% and 75.4%, respectively. In addition, the bound water and toxicity of the hydrogels were also investigated.

     

UV-induced synthesis of chitosan-<Emphasis Type="Italic">g</Emphasis>-polyacrylamide semi-IPN superabsorbent hydrogels

Superabsorbent hydrogels of chitosan-g-polyacrylamide with N,N′-methylene-bis-acrylamide as a crosslinker were prepared via UV irradiation in the absence of photoinitiator under homogeneous conditions. The product was characterized by Fourier transform infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy to confirm the formation of hydrogels. The transparent hydrogels have been observed to exhibit as much as 2987% swelling in acidic solution. In addition, the hydrogel which hydrolyzed for 6 h (0.24 × 10³ min) can have a water uptake of 106 times its weight (5300% swelling for 0.5 g hydrogel). The effect of several variables such as time, temperature, pH, acrylamide/chitosan ratio, crosslinker amount, and different media was explored. Finally, the prepared hydrogel have been used in adsorption of Zn(II) ions from water with high removal efficiency (0.636 meq g⁻¹ or 20.8 mg g⁻¹) at pH = 7. The experimental data of the adsorption equilibrium from Zn(II) solution fit well with the pseudo-second-order model.     

Adsorption capacity,kinetics, and mechanism of copper(II) uptake on gelatin‐based hydrogels

Gelatin‐based hydrogels were synthesized and characterized for use as Cu²⁺‐ion sorbents. Gelatin was crosslinked in the presence of two different monomers, that is, acrylamide (AAm) and/or 2‐hydroxypropyl methacrylate, with N,N‐methylenebisacrylamide, ammonium persulfate, and sodium bicarbonate. The as‐prepared hydrogels were further characterized by scanning electron microscopy, Fourier transform spectroscopy, and the study of their swelling behavior as a function of temperature, time, and pH to evaluate their structure–property relationships. The hydrogels were observed to be good sorbents of Cu²⁺, and a maximum uptake of 84.8% was observed within 2 h at 37°C and with 10 ppm of the Cu²⁺‐ion solution for the gelatin and polyacrylamide hydrogel, which also exhibited the maximum retention capacity at 14.9 mg/g after four feeds. All of the experimental data exhibited good matches with the Langmuir isotherm and followed pseudo‐second‐order kinetics. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Thermoreversible hydrogels XIII: Synthesis and swelling behaviors of [N-isopropylacrylamide-co-sodium 2-acrylamido-2-methylpropyl sulfonate-co-N,N-dimethyl(acrylamido propyl) ammonium propane sulfonate] copolymeric hydrogels

A series of copolymeric hydrogels were prepared from various molar ratios of N-isopropylacrylamide (NIPAAm), sodium-2-acrylamido-2-methylpropyl sulfonate (NaAMPS) and N,N′-dimethyl(acrylamido propyl) ammonium propane sulfonate (DMAAPS). The swelling behaviors of these copolymeric hydrogels were investigated in various saline solutions. The result showed that the phase transition temperatures of these gels changed insignificantly, and the thermosensitivity, in contrast, diminished. In addition, the copolymer gels exhibited polyelectrolytic behavior under lower salt concentration (10⁻⁵∼10⁻¹ M), exhibited a nonionic gel (like NIPAAm) behavior at the salt concentration from 0.1 to 0.4 M, and showed an antipolyelectrolytic behavior (polyzwitterionic effect) at a salt concentration over 0.4 M. Finally, the presented coplymeric gels are investigated for use in drug release application.     

Swelling behaviour and paracetamol release from poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-itaconic acid) hydrogels

Copolymer hydrogels of N-isopropylacrylamide and itaconic acid (IA), crosslinked with N,N′-methylenebisacrylamide, were prepared by radical copolymerization. These hydrogels were investigated with regard to their composition to find materials with satisfactory swelling and drug release properties. A paracetamol is used as a model drug to investigate drug release profile of the hydrogels. It was found that the investigated hydrogels exhibited pH- and temperature-dependent swelling behaviour with restricted swelling and lower equilibrium degree of swelling at lower pH values and temperatures above the LCST value of PNIPAM (around 34 °C). The diffusion exponent for paracetamol release indicate that the mechanism of paracetamol release are governed by Fickian diffusion, while in all release media initial diffusion coefficient was lower than late time diffusion coefficient. Furthermore, the paracetamol release rate depends on the hydrogel degree of swelling and it increased in the first stage of diffusion process, whereas was no significant difference thereafter. The presence of the IA moieties incorporated into the network weakened the shear resistance of the hydrogels. In order to calculate the pore size the characteristic ratio for PNIPAM, C _n  = 11.7, was calculated. Based on the pore size, the investigated hydrogels can be regarded as microporous. According to the obtained results swelling behaviour, mechanical properties, drug-loading capacity and the drug release rate could be controlled by hydrogel composition and crosslinking density, which is important for application of the investigated hydrogels as drug delivery systems.     

Radiation synthesis of kappa-carrageenan/acrylamide graft copolymers as superabsorbents and their possible applications

Kappa-carrageenan (κC) was modified via graft copolymerization of acrylamide (AAm) using γ-irradiation and followed by alkaline hydrolysis to achieve a novel superabsorbent hydrogel. The effect of grafting variables and alkaline hydrolysis conditions such as κC/AAm compositions and irradiation doses, NaOH concentration, hydrolysis time and temperature were systematically optimized to achieve a hydrogel with swelling capacity as high as possible. Swelling properties and FT-IR of untreated κC-g-PAAm and hydrolyzed κC-g-PAAm (H-κC-g-PAAm) were determined. The swelling capacity of hydrolyzed κC-g-PAAm was about 10 times in distilled water and three times in NaCl solution higher than that for κC-g-PAAm. The swelling of superabsorbing hydrogels was examined in buffer solutions. The swelling capacity of hydrogels was also measured in various salt solutions (LiCl, NaCl, KCl, CaCl₂, and FeCl₃). Results indicated that the swelling ratios decreased with an increase in the ion radius, valence and ionic strength of the salt solutions. Due to their high swelling ability in salt solutions, the hydrogels may be referred to as ‘anti-salt superabsorbent’ polymers. Thus, the salinity of water treated with H-κC-g-PAAm hydrogels was determined. It was found that the H-κC-g-PAAm hydrogels have a capability to absorb and retain the fresh water from the saline solution. The results obtained suggested the possible used of such prepared superabsorbent in agricultural purposes as a material for sodic soil remediation.     

Kinetic degradation and controlled drug delivery system studies for sensitive hydrogels prepared by gamma irradiation

Ternary mixtures of N‐vinyl‐2‐pyrrolidone/itaconic acid and gelatin were irradiated by gamma rays at 30 kGy/s and at ambient temperature to prepared poly (NVP/IA and G) hydrogels. Poly (NVP/IA) hydrogels were prepared in different compositions (NVP/IA) mole ratio, (100/0), (98/1.5), (96.5/3.5), and (93/7.0) at 30 kGy. Then adding gelatin at different content (5, 10, 15, 20) mg to the best composition (NVP/IA/H₂O) (93/7)% for the characterization of network structure of these hydrogels, kinetic swelling drug release behavior and Scan Electron Microscope was studied. The equilibrium degree of swelling for P(NVP/IA) and P(NVP/IA/G) copolymer and the swelling‐degradation kinetics were also studies. According to dynamic swelling studies, both the diffusion exponent and the diffusion coefficient increase with increasing content of (IA), whereas, the addition of gelatin to (NVP/IA) composition by different content did not lead to any significant change in swelling percent. Also, the swelling behavior of copolymer hydrogels in response to pH value of the external media was studied, it is noted that the highest swelling values were at pH 4. The in vitro drug release behavior of these hydrogels was examined by quantification analysis with a UV/VIS spectrophotometers. Chlorpromazine hydrochloride was loaded into dried hydrogels to investigate the stimuli‐sensitive property at the specific pH and the drug release profile of these pH‐sensitive hydrogels in vitro. The release studies show that the highest value of release was at pH 4 which can be used for drug delivery system. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Incorporation of acid polymethacrylates into temperature sensitive hydrogels using electron beam irradiation

In this work, electron beam irradiation was used to prepare hydrogels from aqueous solutions of monomers and/or linear polymers. Poly(N-isopropylacrylamide) (PNIPAAm) and polymers of methacrylic acid derivatives were used to generate the different temperature sensitive hydrogels. The effects of irradiation dose and N,N’-methylenebisacrylamide (BIS) crosslinking agent were also studied. The polymethacrylate content in co-polymeric hydrogels was varied (5, 10, 15 and 20 mol%). The temperature dependence of the swelling behavior of the hydrogels was characterized. The influence of polymethacrylate content on the swelling characteristics of the hydrogels was investigated. The incorporation of polymers from methacrylic acid derivatives into hydrogels was effectively achieved under optimum conditions.     

Synthesis and characterization of pH- and thermoresponsive Poly(<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-co-itaconic acid) hydrogels crosslinked with <Emphasis Type="Italic">N</Emphasis>-maleyl chitosan

Biodegradable cross-linker N-maleyl chitosan (N-MACH) was synthesized with chitosan (CS) and maleic anhydride (MA) by acylation. With N-MACH cross-linker, a series of cross-linked poly(N-isopropylacrylamide-co-itaconic acid) [P(NIPAAm-co-IA)] hydrogels were prepared, and their pH-and temperature-responsive behaviors, water contents, swelling/deswelling kinetics were investigated. By alternating the NIPAAm/IA weight ratios, hydrogels had the volume phase transition temperature (VPTT) changed from 33 to 38 °C, whereas cross-linking density did not affect the VPTT apparently. The water content of hydrogels was controlled by the monomer weight ratios of NIPAAm/IA, swelling media, and the cross-linking density. The results of the influence of pH value on the swelling behaviors showed that the minimum swelling ratios of the hydrogels appeared in neutral buffer solution, which was attributed to chemical composition of the hydrogels and the swelling media. In the swelling/deswelling kinetics, all the dried hydrogels exhibited fast swelling within 480 min and fast deswelling within 20 min, which was independent of the content of IA and cross-linker.     

Semi‐interpenetrating networks based on poly(N‐isopropyl acrylamide) and poly(N‐vinylpyrrolidone)

Three series of novel semi‐interpenetrating polymer networks, based on crosslinked poly(N‐isopropylacrylamide), PNIPA, and different amounts of the linear poly(N‐vinylpyrrolidone), PVP, were synthesized to improve the mechanical properties and thermal response of PNIPA gels. The effect of the incorporation of the linear PVP into the temperature responsive networks on the temperature‐induced transition, swelling/deswelling behavior, and mechanical properties was studied. Polymer networks with four different crosslinking densities were prepared with varying molar ratios (25/1 to 100/1) of the monomer (N‐isopropylacrylamide) to the crosslinker (N,N′‐methylenebisacrylamide). The hydrogels were characterized by determination of the equilibrium degree of swelling, the dynamic shear modulus and the effective crosslinking density, as well as tensile strength and elongation at break. Furthermore, the deswelling kinetics of the hydrogels was studied by measuring their water retention capacity. The inclusion of the linear hydrophilic PVP in the PNIPA networks increased the equilibrium degree of swelling. The tensile strength of the semi‐interpenetrating networks (SIPNs) reinforced with linear PVP was higher than that of the PNIPA networks. The elongation at break of these SIPNs varied between 22% and 55%, which are 22 – 41% larger than those for pure PNIPA networks. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Swelling behavior of semi‐interpenetrating polymer network hydrogels composed of poly(vinyl alcohol) and poly(acrylamide‐co‐sodium methacrylate)

Interpenetrating polymer network (IPN) hydrogels based on poly(vinyl alcohol) (PVA) and poly(acrylamide‐co‐sodium methacrylate) poly(AAm‐co‐SMA) were prepared by the semi IPN method. These IPN hydrogels were prepared by polymerizing aqueous solution of acrylamide and sodium methacrylate, using ammonium persulphate/N,N,N¹,N¹‐tetramethylethylenediamine (APS/TMEDA) initiating system and N,N¹‐methylene‐bisacrylamide (MBA) as a crosslinker in the presence of a host polymer, poly(vinyl alcohol). The influence of reaction conditions, such as the concentration of PVA, sodium methacrylate, crosslinker, initiator, and reaction temperature, on the swelling behavior of these IPNs was investigated in detail. The results showed that the IPN hydrogels exhibited different swelling behavior as the reaction conditions varied. To verify the structural difference in the IPN hydrogels, scanning electron microscopy (SEM) was used to identify the morphological changes in the IPN as the concentration of crosslinker varied. In addition to MBA, two other crosslinkers were also employed in the preparation of IPNs to illustrate the difference in their swelling phenomena. The swelling kinetics, equilibrium water content, and water transport mechanism of all the IPN hydrogels were investigated. IPN hydrogels being ionic in nature, the swelling behavior was significantly affected by environmental conditions, such as temperature, ionic strength, and pH of the swelling medium. Further, their swelling behavior was also examined in different physiological bio‐fluids. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 302–314, 2005     

UV photopolymerized hydrogels with β-cyclodextrin moieties

Hydrophilic hydrogels based on poly(ethylene glycol)–poly(propylene glycol)–poly(ethylene glycol) block copolymers have potential applications in drug delivery, tissue engineering and other biomedical devices due to their excellent biocompatibility and environmental sensitivity. However, they also exhibit some shortcomings in terms of swelling and mechanical properties as well as affinity for water-insoluble or hydrophobic drug molecules. To address these limitations, new polymeric hydrogels with β-cyclodextrin moieties were prepared by UV photo-polymerization of maleic anhydride-substituted β-CD (MAH-CD) and the block copolymer macromer from Pluronic F68 and poly(ɛ-caprolactone). Their swelling and dynamic rheological properties were investigated with respect to the effects of feed compositions. It was found that the swelling ratio, storage modulus and loss modulus of the resulting hydrogel increased with the increase of MAH-CD amount. Incorporation of MAH-CD resulted in strong viscoelastic system with dominating elastic behavior.     

Removal of cationic dyes from aqueous solutions with poly (<Emphasis Type="Italic">N</Emphasis>-isopropylacrylamide-<Emphasis Type="Italic">co</Emphasis>-itaconic acid) hydrogels

In this study, N-isopropylacrylamide-based temperature and pH-sensitive hydrogels were synthesized by free radical polymerization for removal of cationic dyes from aqueous solutions. For this purpose, N-isopropylacrylamide was copolymerized with various amounts of sodium salt of itaconic acid in the presence of crosslinking agent (N,N-methylene bisacrylamide). The chemical structures of hydrogels were characterized by FT-IR analysis. In order to investigate swelling properties of the hydrogels, water absorption (swelling) and shrinking (deswelling) kinetics, the equilibrium swelling ratios in water and different pH buffer solutions, and the temperature dependent swelling ratios were determined. Then, their adsorption properties such as adsorption capacities, kinetics, isotherms were investigated in case of their usage in removal of Safranine T (ST), Brilliant Green (BG), and Brilliant Cresyl Blue (BCB) aqueous solutions. According to adsorbed dye amount, the adsorption capacities are followed the order BG > ST ≅ BCB. In addition, the results indicated that the pseudo-second-order kinetic model fitted better than the data obtained from pseudo-first-order model for the adsorption of all dyes onto hydrogels. Furthermore, according to effect of the initial dye concentration findings, it is concluded that, Freundlich isotherm explains the adsorption better than Langmuir isotherm.     

In vitro dynamic swelling behaviors of polyhydroxamic acid hydrogels in the simulated physiological body fluids

Summary Influence of some simulated physiological body fluids on the dynamic swelling behaviour of polyelectrolytic hydroxamic acid hydrogels (PHA) was investigated at 37 °C in vitro. The simulated physiological body fluids are distilled water, human sera, physiological saline (0.89 % NaCl), isoosmotic phosphate buffer at pH 7.4, gastric fluid at pH 1. 1, (gylicine-HCl buffer), urea (0.3 mol L⁻¹), and the aquatic solutions of K₂HPO₄ and KNO₃ (the sources of K+). The values of equilibrium swelling of PHA hydrogels varied in the range of 130–4625%, while the values of equilibrium fluid content of the hydrogels varied in the range of 57–97%. The initial rate of swelling, diffusional exponent, and, diffusion coefficient were calculated using swelling kinetics data. Diffusion of the fluids into the hydrogel was found to be non-Fickian character. The diffusion coefficients of the hydrogel varied between 0.6×10⁻⁶– 8.1×10⁻⁶ cm² s⁻¹. Received: 15 March 2000/Accepted: 18 December 2000     

Synthesis and super-swelling behavior of a novel protein-based superabsorbent hydrogel

Summary In this work, we synthesize a novel protein-based superabsorbent hydrogel and study its swelling behavior. The crosslinking graft copolymerization of acrylic acid (AA) onto the hydrolyzed collagen as a protein backbone was carried out in a homogeneous medium. Potassium persulfate (KPS) as an initiator and N,N^′-methylene bisacrylamide (MBA) as a crosslinker were used. The product’s structure was established using FTIR spectroscopy. We were systematically optimized the certain variables of the graft copolymerization (i.e. the monomer, the initiator, and the crosslinker concentration) to achieve a hydrogel with maximum swelling capacity. Under this condition, maximum capacity of swelling in distilled water was found to be 920 g/g. Morphology of the optimized sample was examined by scanning electron microscopy (SEM). The swelling ratio in various salt solutions was also determined. Additionally, the swelling of superabsorbing hydrogels was measured in solutions with pH ranged from 1 to 13. The synthesized hydrogel exhibited a pH-responsiveness character so that a swelling-collapsing pulsatile behavior was recorded at pH 2 and 8.     

Stimuli-responsive poly(N-isopropylacrylamide-co-sodium acrylate) hydrogels: A swelling study in surfactant and polymer solutions

Stimuli-responsive poly(N-isopropylacrylamide-co-sodium acrylate) [poly(NIPAM-co-SA)] hydrogel networks were prepared by aqueous free-radical copolymerization using the ammonium persulfate/N,N,N¹,N¹-tetramethylethylenediamine (APS/TMEDA) redox-pair initiator system in the presence of different amounts of N,N¹-methylenebisacrylamide (MBA) crosslinker. Higher swelling capacities were availed for these N-isopropylacrylamide-based hydrogels due to the presence of the hydrophilic poly(sodium acrylate) anionic units. In this the swelling phenomena of hydrogels in different surfactant and polymer solutions are investigated in a systematic way. The structural variation as well as the thermal stability of the surfactant-modified hydrogels were studied in detail. Further, the hydrogels swelling/diffusion kinetic parameters were investigated and a non-Fickian type of diffusion characteristics was found in all the swelling media for the diffusion of water into these hydrogels.     

Synthesis and characterization of poly(N‐vinyl imidazole) hydrogels crosslinked by gamma irradiation

Crosslinked poly(N‐vinyl imidazole) (PVIm) hydrogels in the form of rods have been prepared by ⁶⁰Co γ‐radiation initiated simultaneous polymerization and crosslinking of N‐vinyl imidazole in bulk and water. In binary aqueous systems, the percentage gelation decreased with increasing water content. The PVIm hydrogels synthesized were further protonated in HCl solutions of different concentration. PVIm and protonated PVIm (H‐PVIm) hydrogels have been characterized using spectroscopic and thermal methods, and the swelling behaviour of these two types of hydrogel has been investigated. PVIm hydrogels originally swelled to 600% (by volume) but in their protonated form at pH 7.0 reached 4000% swelling. © 2002 Society of Chemical Industry     

Formulation design,optimization, characterization and swelling behaviour of a cationic superabsorbent based on a copolymer of [3‐(methacryloylamino)propyl]trimethylammonium chloride and acrylamide

A series of crosslinked copolymers with cationic nature have been prepared based on acrylamide (AAm) and [3‐(methacryloylamino)propyl]trimethyl ammonium chloride (MAPTAC) using N,N′ methylene‐bis‐acrylamide (MBA) as crosslinking agent. Taguchi's method has been employed for the purpose of formulation design and optimization as well as investigating the effects of various compositional parameters, such as total monomer concentration, cationic monomer and crosslinking agent concentration. The swelling behaviour of the synthesized gels in electrolyte solutions composed of ions with different valency has been studied and compared with an anionic‐based superabsorbent. The swelling capacity and absorbency were found to be enhanced with increase of the MAPTAC moieties of the copolymer chains, and therefore increase of their cationic character. All the cationic hydrogels prepared had greater swelling capacity, with less change in their swelling behaviour, when immersed into aqueous solutions containing multivalent cations. The anionic‐based hydrogels collapsed in similar ionic solutions with moderate‐to‐high ionic strength and did not show any tendency to re‐swell. The complex modulus (G*) of the crosslinked copolymers in the equilibrium swollen state was measured by rheomechanical spectroscopy and was correlated with the chemical composition of the network. Thermogravimetric analysis of the dry cationic superabsorbent showed more bound water but similar thermal behaviour to crosslinked polyacrylamide Copyright © 2003 Society of Chemical Industry     

Preparation and characterization of PVA/PVP/glycerin/antibacterial agent hydrogels using <Emphasis Type="Italic">γ</Emphasis>-irradiation followed by freeze-thawing

Hydrogels for wound dressings from a mixture of poly(vinyl alcohol) (PVA), poly(N-vinylpyrrolidone) (PVP), glycerin and an antibacterial agent were obtained by a γ-irradiation combined with freeze-thawing. The physical properties such as the gelation and swelling degree of the hydrogels were examined. When the PVP/PVA ratio was 6: 4 (wt%) and prepared by combined irradiation and freeze-thawing, it showed an excellent swelling capacity (>1,200%). The antibacterial effect of the hydrogels containing the antibacterial agents was observed to be effective as the concentration of antibacterial agents increased. The results demonstrated that hydrogel in a proper blending ratio could be used as a wound dressing that can accelerate wound healing with an antibacterial effect.     

Network structure and temperature dependence swelling behavior of PEG-b-Poly (NIPAM-co-AMPSA) hydrogels in water

Temperature sensitive hydrogels were prepared by free radical polymerization of N-isopropylacrylamide (NIPAM) and 2-acrylamido-2-methylpropanesulphonic acid (AMPSA) in presence of polyethylene glycol (PEG) as macroinitiator. The aim of the work reported here was to investigate temperature sensitive swelling and deswelling behaviors of the hydrogels in water in order to investigate the effect of various amounts of AMPSA. The result indicated that the incorporation of a hydrophilic ionizable comonomer (AMPSA) affects the temperature sensitivity, swelling/deswelling, morphology and network structure of the hydrogels. The volume fraction in the swollen state (V_2m), the number average molecular weight between cross-links ([`(M)]_c {\overline M_c} ), the number of segments between the cross-linked point (N), polymer-solvent interaction parameter (χ), enthalpy (ΔH) and entropy (ΔS) were determined using the Flory-Rehner theory at equilibrium swelling. The negative values of ΔH and ΔS showed that the prepared hydrogels had lower critical solution temperature (LCST). The Flory-Rehner theory of swelling equilibrium was qualitatively satisfied with the experimental data of hydrogels at different temperature.