Preparation and characterization of 2‐hydroxyethyl methacrylate‐based porous copolymeric particles

2‐Hydroxyethyl methacrylate was copolymerized with three different comonomers, methyl methacrylate (MMA), styrene (St), and N‐vinyl‐2‐pyrrolidone (NVP), respectively, to prepare porous particles crosslinked using ethylene glycol dimethacrylate (EGDMA) in the presence of an organic solvent, 1‐octanol (porogen), by means of suspension copolymerization in an aqueous phase initiated by 2,2‐azobisisobutyronitrile. Nano‐pores were observed in the particles. The pore size and the swelling properties of these particles can be controlled by changing comonomers or adjusting the crosslinker or porogen concentration. A lower crosslinker or porogen concentration favors generating smaller pores, whereas a higher concentration of a hydrophilic comonomer, higher concentration of crosslinker, and higher porogen volume ratio promote the generation of larger pores. In addition, the effects of the porous characteristics on the swelling properties were explored. The swelling capacity of the porous particles is reduced with the increase in the crosslinker concentration; however, there is a critical porogen volume ratio, in which the maximal swelling capacity is reached. Higher porosity in the particles and higher amount of hydrophilic comonomer favor a higher swelling capacity of the particles. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Effects of cyclization and pendant vinyl group reactivity on the swelling behavior of polyacrylamide gels

A series of polyacrylamide (PAAm) gels were prepared by free-radical crosslinking copolymerization of acrylamide and N,N′-methylenebis(acrylamide) (BAAm) in water at various crosslinker (BAAm) and chain transfer agent (isopropyl alcohol, IPA) concentrations. It was shown that only 5% of the crosslinker used in the feed forms effective crosslinks in the final hydrogels. At BAAm contents as high as 3 mole%, the equilibrium swelling ratio of the gels in water is independent of the crosslinker content in the feed. This is due to the prevailing multiple crosslinking reactions during the gel formation process. At a fixed crosslinker content, the onset of gelation is shifted towards higher conversions and reaction times as the amount of IPA increases. Addition of IPA in the monomer mixture also increases the equilibrium swelling ratio of PAAm gels. It was shown that the gel crosslinking density increases on rising IPA concentration in the feed due to the increasing rate of intermolecular crosslinking reactions. Received: 30 May 1997/Accepted: 26 June 1997     

Characteristics of permeation and separation of aqueous alcoholic solutions through a poly[bis(2,2,2-trifluoroethoxy)phosphazene] membrane by evapomeation and pervaporation

The characteristics of permeation and separation for aqueous solutions of methanol and ethanol through a poly[bis(2,2,2-trifluoroethoxy)phosphazene] (PBTFP) membrane were studied by pervaporation and evapomeation. In pervaporation technique, methanol was preferentially permeated in all of the feed solution compositions and ethanol was permeated in lower ethanol concentrations of the feed solution. Water was predominantly permeated from the feed solutions with higher ethanol concentration. In evapomeation technique, water was selectively permeated in both all of the feed vapor compositions for aqueous methanol and ethanol solutions. These different permselectivities depended on the feed composition and the membrane permeation technique and could be discussed by a difference in the mechanisms of permeation and separation. It was found that the permeation rate was influenced remarkably by the degree of swelling of the PBTFP membrane and the permselectivity for water of aqueous alcoholic solutions was enhanced by an increasing degree of swelling of the membrane. When the degree of swelling of the membrane with rising permeation temperature was small, both the permeation rate and permselectivity for alcohol in pervaporation and evapomeation increased with the permeation temperature. The above results are discussed considering the PBTFP membrane structure in evapomeation and pervaporation.     

Membrane Design for Direct Ethanol Fuel Cells: A Hybrid Proton‐Conducting Interpenetrating Polymer Network

A series of hybrid proton‐conducting membranes with an interpenetrating polymer network (IPN) structure was designed with the direct ethanol fuel cell (DEFC) application in mind. In these membranes, glutaraldehyde crosslinked poly(vinyl alcohol) (PVA) were interpenetrated with the copolymer of 2‐acrylamido‐2‐methyl‐propanesulphonic acid (AMPS) and 2‐hydroxyethyl methacrylate (HEMA) crosslinked by poly(ethylene glycol) dimethacrylate (PEGDMA). Silica from the in situ sol–gel hydrolysis of tetraethyl orthosilicate (TEOS) was uniformly dispersed in the polymer matrix. The membranes fabricated as such had ion exchange capacities of 0.84–1.43 meq g^–1 and proton conductivities of 0.02–0.11 S cm^–1. The membranes exhibited significantly lower fuel permeabilities than that of Nafion. In a manner totally unlike Nafion, fuel permeabilities were lower at higher fuel concentrations, and were lower in ethanol than methanol solutions. These behaviours are all relatable to the unique swelling characteristics of PVA (no swelling in ethanol, partial swelling in methanol and extensive swelling in water) and to the fuel blocking and swelling suppression properties of silica particles. The membranes are promising for DEFC applications since a high concentration of fuel may be used to reduce fuel crossover and to improve the anode kinetics for a resultant increase in both the energy and power densities of the fuel cell.     

Alcohophilic gels: Polymeric organogels composing carboxylic and sulfonic acid groups

Polymeric organogels based on acrylic acid (AA) and sodium allyl sulfonate (SAS) were prepared through solution polymerization using a persulfate initiator and a polyethylene glycol diacrylate (PEGDA) crosslinker. FTIR spectroscopy, elemental, and rheological analyses were used for a preliminary characterization. Thermo‐mechanical analysis was also carried out for characterizing samples. Glass transition temperature (T_g) of copolymer was decreased after acid treatment which could be attributed to detachment of ion pairs during the post‐treatment. Due to counterion binding of Na⁺ to form ionomer, the poly(AA‐SAS) gels showed no polyelectrolyte behavior to have high swelling capacity in conventional alcohols, i.e., ethanol and methanol. It was postulated that modification via removing Na⁺ could help breaking ion pair aggregates which leads to swelling enhancement. Thus, poly(AA‐SAS) was treated with hydrochloric acid to remove (Na⁺) counterions. This modification led to the gel transform from ionomer regime to a polyelectrolyte regime in which free mobile ions were existed in the network. The gel swelling capacity was increased due to raise of mobile ions after the treatment. It was found that both of the acid concentration and treatment time had constructive influence on the gel alcohophilicity. The acid‐treated samples could imbibe ethanol and methanol as high as 25.8 and 39.5 g/g, respectively. They may be superior candidates for applications such as pharmaceuticals gels and fire starters. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Temperature sensitive poly(N-t-butylacrylamide-co-acrylamide) hydrogels: synthesis and swelling behavior

A series of temperature sensitive hydrogels was prepared by free-radical crosslinking copolymerization of N-t-butylacrylamide (TBA) and acrylamide in methanol. N,N′-methylenebis(acrylamide) was used as the crosslinker. It was shown that the swelling behavior of the hydrogels can be controlled by changing the amount of TBA units in the network chains. Hydrogels immersed in dimethylsulfoxide (DMSO)-water mixtures exhibited reentrant swelling behavior, in which the gels first deswell then reswell if the DMSO content of the solvent mixture is continuously increased. In water over the temperature range of 2-64 °C, hydrogels with less than 40[percnt] TBA by mole were in a swollen state while those with TBA contents higher than 60[percnt] were in a collapsed state. Hydrogels with 40-60[percnt] TBA exhibited swelling-deswelling transition in water depending on the temperature. The temperature interval for the deswelling transition of 60[percnt] TBA gel was found to be in the range from 10 to 28 °C, while for the 40[percnt] TBA gel, the deswelling started at about 20 °C and continued until the onset of the hydrolysis of the network chains at around 64 °C. It was shown that the Flory-Rehner theory of swelling equilibrium provides a satisfactory agreement to the experimental swelling data of the hydrogels, provided that the sensitive dependence of the χ parameter on both temperature and polymer concentration is taken into account.     

Natural rubber/poly(acrylic acid) semi‐interpenetrating polymer network membranes for the pervaporation of water–ethanol mixtures

Pervaporation membranes for the dehydration of water–ethanol mixtures were prepared from a semi‐interpenetrating polymer network (semi‐IPN) of natural rubber (NR) and crosslinked poly(acrylic acid) (PAA). The swelling studies revealed that hydrophilic PAA present in the semi‐IPN membranes caused the membranes to swell greatly in water. The swelling degree of the membranes in water was significantly affected by the amount ratio between the hydrophobic NR and the hydrophilic PAA. The sorption experiments of the NR/PAA membranes in various concentrations of water–ethanol mixtures suggested the preferential sorption to water. However, for the membrane with high PAA content, the water sorption selectivity decreased considerably at high water concentration of water–ethanol mixtures because the membrane was in the highly swollen state. Pervaporation separations of water–ethanol mixtures using NR/PAA membranes were performed and it was found that at low water concentrations of feed mixtures, increasing the PAA content of the membrane can enhance both water permeation flux and selectivity. Additionally, under low feed water concentration, increasing the feed temperature would increase the water flux with the decreasing of the ethanol flux. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Effect of crosslinking concentration on mechanical and thermodynamic properties in acrylic acid–co–methyl methacrylate hydrogels

The mechanical and thermodynamic properties of poly(acrylic acid‐co‐methyl methacrylate) hydrogels with varying crosslinker N,N′‐methylenebisacrylamide (NMBA) content are reported. A higher NMBA content generally led to a stronger and harder gel with lower water content. Swelling capacity decreased as the NMBA concentration increased between 0.5% and 2%, remaining constant beyond this range. The temperature changes of the partial molar Gibbs free energy of dilution and enthalpic and entropic contributions were examined. The thermodynamic parameters showed that swelling was an unfavorable and endothermic process. The freezing and nonfreezing water in the hydrogel was determined by differential scanning calorimetry (DSC). Freezing water content decreased with increasing crosslinker (NMBA) content, whereas the ratio of nonfreezing water to total water content increased with NMBA content because of the promoting of hydrophobic interactions in the hydrogels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4016–4022, 2006     

Non-Gaussian elasticity of poly(2-acrylamido-2-methylpropane sulfonic acid) gels

Summary A series of strong polyelectrolyte hydrogels was prepared from the sodium salt of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) as the monomer and N,N-methylene(bis)acrylamide (BAAm) as a crosslinker. The hydrogels prepared between 9 and 50 mol % BAAm appeared homogeneous to eye but exhibited large spatial fluctuations of polymer concentration, as determined by the light scattering measurements. The elasticity tests show that the modulus of elasticity of gels increases with increasing degree of swelling, starting from the gel preparation state. Thus, the mechanical properties of the hydrogels are improved on their swelling in water. It was shown that the hydrogels even at a gel state just after their preparation are in the non-Gaussian regime due to the high degree of spatial gel inhomogeneity.     

Mixed matrix membranes prepared from natural rubber/poly(vinyl alcohol) semi-interpenetrating polymer network (NR/PVA semi-IPN) incorporating with zeolite 4A for the pervaporation dehydration of water-ethanol mixtures

The pervaporation dehydration of water-ethanol mixtures was investigated using the mixed matrix (MM) membranes prepared from natural rubber (NR) and crosslinked poly(vinyl alcohol) (PVA) semi-IPN embedded with the zeolite 4A. With the presence of NR as well as zeolite, the swelling of MM membranes in water was effectively suppressed. Examined by DSC, the non-freezing bound water in the MM membranes was found decreasing with more zeolite loading because the water-polymer interaction is diminishing. The sorption study of MM membranes revealed a preferential sorption to water with improved water sorption selectivity as increasing the zeolite loading. For pervaporation at 5 vol% water in feed, the reversed trade-off with respect to the zeolite loading was encountered such that the total permeation flux increased along with an enhancement of the water separation factor. For higher feed water concentration, despite the greater total permeation flux, the separation factor was reduced owing to the extensive swelling of the polymer matrix. The temperature dependency of the partial water and ethanol fluxes followed the Arrhenius relationship and the estimated activation energies for water flux were lower than those of the ethanol flux, suggesting that the developed MM membranes are highly water selective.     

Solvent-, ion- and pH-specific swelling of poly(2-acrylamido-2-methylpropane sulfonic acid) superabsorbing gels

Homopolymer hydrogel of 2-acrylamido-2-methylpropane sulfonic acid (AMPS) and its nanocomposite counterpart were prepared to study their swelling properties. The hydrogels showed ability to absorb and retain electrolytes as well as binary mixtures of water and organic solvents (i.e., methanol, ethanol, acetone, ethylene glycol (EG), polyethylene glycol, N-methyl-2-pyrrolidone (NMP), and dimethylsulfoxide (DMSO). The nanocomposite gel exhibited lower swelling in all solvent compositions in comparison with non-composite gel. Unlike conventional acrylic acid-based hydrogels, the poly(AMPS) gels showed superabsorbing capacity in pure ethanol, methanol, EG, DMSO and NMP. Meanwhile, swelling capacity of poly(AMPS) hydrogel in DMSO-water mixtures was surprisingly found to be even higher than that in water. This extraordinary superswelling behavior was explained based on the interactions involved in solvation as well as the solubility parameters. The gels showed pH-independent superabsorbency in a wide range of pH (3–11). Saline-induced swelling transitions were also investigated and the ionic interactions were confirmed by FTIR spectroscopy.     

Conformation of polyacrylamide in aqueous solution with interactive additives and cosolvents

The viscosity of polyacrylamide (PAM) dilute aqueous solutions with NaCl, glucose, and SDS as additives was measured by Ubbelohde viscometry. There was linear relationship between reduced viscosity vs. PAM concentration in aqueous solutions. The Huggins constant k and intrinsic viscosity [η] were used to study the conformation of the polymer chains and the degree of polymer–solvent interaction. In addition, the viscosity of diluted PAM solutions in water with acetone, ethanol, DMF, and ethylene glycol as cosolvent was measured. It was found that the polymer chain conformation contracted as the acetone, ethanol, and DMF cosolvent composition ratio increased, but there was no distinguishing difference between water–ethylene glycol compositions. The solution properties of PAM were used to estimate the swelling properties of PAM gel in the same external conditions, as gel is formed by crosslinking of linear polymer. In good solvent the polymer chain should be expanded, and gel is expected to have large swelling ratio. In water cosolvent systems, when the linear polymer chain underwent coil–globule transition, PAM gel should have volume phase transition under corresponding external conditions. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 3122–3129, 2003     

Hydrogel characteristics of a novel temperature‐sensitive polymer,poly(N‐2‐methoxyisopropylacrylamide)

In this study, a novel temperature‐sensitive polymer, poly(N‐2‐methoxyisopropylacrylamide), PNMIPA, in the crosslinked hydrogel form was obtained. The monomer, N‐2‐methoxyisopropylacrylamide (NMIPA) was synthesized by the nucleophilic substitution reactions of acryloyl chloride with 2‐methoxyisopropylamine. Hydrogel matrix of PNMIPA was obtained by the bulk polymerization method. The bulk polymerization experiments were performed at +4°C, by using N,N‐methylenebisacrylamide (MBA) as crosslinker, polyethyleneglycol (PEG) 4000 as diluent, and potassium persulfate (KPS) and tetramethylethylenediamine (TEMED) as the initiator and accelerator, respectively. The same polymerization procedures were applied by changing monomer, initiator, crosslinker and diluent concentrations in order to obtain crosslinked gel structures having different temperature–sensitivity properties. The equilibrium swelling ratio of PNIMPA gel matrices at constant temperature increased with increasing initiator concentration and decreasing monomer concentration. The use of PEG 4000 as diluent in the gel synthesis resulted in about two times increase in equilibrium swelling ratios in the low temperature region. A decrease in the equilibrium swelling ratios of gel matrices started at 30°C and the decrease became insignificant at 55°C. Temperature‐sensitivities were determined in two different media. Distilled water medium was used in order to observe the temperature‐sensitivity of the gel clearly and the phosphate buffer medium was used in order to represent the temperature‐sensitive swelling behavior of the gel when it is used in biological media. Step effect was applied on ambient temperature in two opposite directions in order to examine the dynamic swelling and shrinking behaviors of the gels. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Pervaporation separation of binary and ternary mixtures with polydimethylsiloxane membranes

This study dealt with the separation of binary water–phenol and water–methanol mixtures and ternary water–phenol–methanol mixtures by pervaporation (PV) with polydimethylsiloxane (PDMS) membranes. The effects of the operating conditions (feed temperature, feed concentration, and feed flow rate) on the separation performance for binary mixtures were investigated. An increase in temperature or concentration increased the total permeation flux and decreased the organic separation factor. In other words, an increase in the temperature or feed organic concentration increased the water flux more significantly than the organic compound flux, which resulted in a separation factor reduction. Also, an increase in the feed flow rate increased the total flux and separation factor because the boundary layer effects diminished. The vapor–liquid equilibrium separation factor (α_VLE) and pervaporation separation factor (α_PV) values for the PDMS membrane were calculated, and this showed that α_PV for the water–phenol mixture was greater than α_VLE. This means that the membrane was highly efficient for the PV separation of phenol from dilute aqueous solutions relative to the separation of methanol. This was due to the fact that phenol has a higher solubility parameter than methanol in silicone membranes. To study the effect of a third component on membrane performance, PV experiments were also carried out with water–phenol–methanol mixtures. The results for total permeation flux and the phenol separation factor for PDMS membranes in contact with water–phenol–methanol ternary mixtures are similar to those in contact with water–phenol binary mixtures. The phenol separation factor of the membrane in contact with the ternary mixture was slightly lower than that in contact with the binary mixture. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Crosslinker reactivity and the structure of superabsorbent gels

A ¹³C-labeled crosslinker (trimethylolpropane triacrylate, TMPTA) was synthesized and copolymerized with acrylic acid while monitoring the relative rates of reaction of the crosslinker and acrylic acid by ¹³C-NMR. This allowed easy quantification of the concentration of the minor component (crosslinker) in the polymer and monomer mixture to levels as low as 0.02%. Polymerizations were conducted in 5 mm NMR tubes under varied temperature, percent neutralization (pH), and percent solids. Reactivity ratios were determined from the rates of incorporation of the components into the gel by use of the integrated form of the copolymerization equation, and their sensitivity to the above variables was quantified. The relative rate of incorporation of the crosslinker into the gel was exceedingly fast. The reactivity ratio, r₁ for acrylic acid, varied from 0.31 (65% neutralization) to 0.77 (unneutralized). The reactivity ratio was affected by the percent solids (solvent effect), but was insensitive to temperature over the range of 55–80°C. It was observed that all of the double bonds of TMPTA were incorporated into gel network as opposed to prior models predicting only two bonds reacting. The reported inefficiency of TMPTA is postulated to be caused by a solubility problem in the monomer mixture. Very low levels of extractables were found in the products even though the crosslinker was consumed by 70% conversion. Based on these data, we propose that a major component of the gel network is graft polymer that forms late in the polymerization onto the crosslinked gel formed earlier. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 439–451, 1997     

Starch‐poly(acrylamide‐co‐2‐acrylamido‐2‐methylpropanesulfonic acid) graft copolymers prepared by reactive extrusion

Graft copolymers of starch with acrylamide and 2‐acrylamido‐2‐methylpropanesulfonic acid (AMPS) were prepared by reactive extrusion in a twin‐screw extruder. The weight ratio of total monomer to starch was fixed at 1 : 3, while the molar fraction of AMPS in the monomer feed ranged from 0 to 0.119. Monomer to polymer conversions were 85% or greater, with grafting efficiencies of 68% (highest AMPS content) to 85% (no AMPS). Absorbency in distilled water at pH 7 increased linearly with the mole fraction AMPS in the grafted polymer, while absorbencies in 0.9% NaCl were independent of AMPS content. When swollen in water/ethanol mixtures, swelling decreased gradually with increasing ethanol volume fraction, followed by a large decrease over a narrow ethanol concentration. This behavior is similar to that observed for AMPS‐acrylamide gels. The swelling properties suggest these graft copolymers may have applications as responsive materials. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42405.     

Effects of synthesis‐solvent composition and initiator concentration on the swelling behaviour of poly(N‐isopropylacrylamide) P(NIPAAM), poly(NIPAAM‐co‐dimethyl itaconate), and poly(NIPAAM‐co itaconic acid) gels

The effects of synthesis‐solvent composition, initiator concentration, comonomer type and monomer purity on the volume swelling ratios, and polymer‐solvent interaction parameter χ have been investigated as a function of temperature. Non‐ionic N‐isopropylacrylamide (NIPAAM) homopolymer gels, poly[NIPAAM‐co‐(dimethyl itaconate)] (P(NIPAAM‐co‐DMI)) and poly[NIPAAM‐co‐(itaconic acid)] (P(NIPAAM‐co‐IA)) gels containing hydrophobic (DMI) and hydrophilic (IA) comonomers were prepared by free radical polymerization using potassium persulfate (KPS) –N, N, N′, N′‐tetramethyl ethylene diamine (TEMED) (redox initiator) in the presence of an N, N′‐methylene bis(acrylamide) (MBAAM) cross‐linking agent. The synthesis‐solvent composition (40/60 mixture of water/methanol and water) and initiator concentration employed significantly affected the properties of the NIPAAM gels. The transition temperatures of P(NIPAAM‐co‐IA) gels synthesized in water/methanol mixture were higher than that of the gel obtained in water. Furthermore, χ values of the NIPAAM homopolymer gel prepared with higher KPS content was an increasing function of temperature, while χ values of the sample obtained with lower initiator concentration changed around a critical solubility value 0.50. The results obtained also show that the interactions between monomer and solvent molecules in the reaction media (ie composition of the pregel solution) have an important effect on the formation and properties of the network structure (ie pore sizes of the gels). © 2000 Society of Chemical Industry     

Studies on poly(acrylic acid)/attapulgite superabsorbent composites. II. Swelling behaviors of superabsorbent composites in saline solutions and hydrophilic solvent–water mixtures

The effect of the attapulgite content on the swelling for a series of poly(acrylic acid)/attapulgite superabsorbent composites in water was studied. The effects of the temperature and pH values on the water absorbency of the superabsorbent composites were investigated. The swelling behavior of the superabsorbent composites in various saline solutions was also investigated. The water absorbency in various salt solutions decreased with an increase in the ionic strength of the solutions. At a high ionic strength (>1 × 10^?3M), the water absorbency in monovalent cationic solutions was higher than that in multivalent cation solutions. This dramatic reduction of the water absorbency in multivalent cationic solutions of high ionic strength may have been due to the complexing ability of the carboxylate groups inducing the formation of intramolecular and intermolecular complexes, which resulted in an increased crosslink density of the network. The swelling behavior of the superabsorbent composites in mixtures of water and hydrophilic solvents, including methanol, acetone, ethanol, and dimethyl sulfoxide (DMSO), was also investigated. The water absorbency decreased with an increase in the concentration of any of the four organic solvents, and two transitions were observed in the superabsorbent composite/hydrophilic solvent–water mixture systems. The main transition for the four hydrophilic solvent–water mixtures was a collapse of the swollen gel (at 50–80% methanol, 30–80% acetone, 50–80% ethanol, and 50–80% DMSO). For the methanol–water system, the magnitudes of the first and second transitions for the poly(acrylic acid)/attapulgite superabsorbent composites containing lower proportions of attapulgite were larger than those for the superabsorbent composites with higher attapulgite contents. The effect of the mixture temperature on the water absorbency of the superabsorbent composites in 10 min was also reported. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 94: 1869–1876, 2004     

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.     

Effect of chemical crosslinking on swelling parameters of modified poly(vinyl alcohol) hydrogel

Graft copolymerization of maleic anhydride (MA) onto partially and fully hydrolyzed poly(vinyl alcohol), PVA, was carried out in presence and in absence of an initiator. The structural features of these grafts were confirmed by 1 HNMR analysis. 1 HNMR analysis was also used to determine the percentage of grafting. These grafts were crosslinked using different concentrations of either 1,1,1-trimethylolpropane trimethacrylate (TPT) or methylene bisacrylamide (MBA) as Hexa- or tetra-functional crosslinker, respectively. The crosslinkers concentrations ranged from 1% to 30% (wt.%) based on the total weight of grafts. The final water content, volume fraction of the polymer and swelling capacity were determined for all grafts. The effect of MBA and TPT crosslinkers structure on swelling properties of both partially and fully hydrolyzed PVA grafts were also determined.