Superabsorbent polymeric materials. XI. Effect of nonionic monomers on the swelling behavior of crosslinked poly(sodium acrylate‐co‐nonionic monomers) in aqueous salt solutions

A series of xerogels based on sodium acrylate, nonionic monomers such as 2‐hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) methacrylate (PEGMA), and N,N′‐methylene bisacrylamide were prepared by inverse suspension polymerization. The results indicate that the water absorbencies for these two gel series were effectively improved by the addition of a small amount of nonionic monomer (HEMA or PEGMA). The initial absorption rates in deionized water were faster for the PEGMA gels than for the HEMA gels. Scanning electron microscopy showed that the spherical particle size was smaller for the PEGMA gels than for the HEMA gels. In addition, the water absorbency of the gels in various salt solutions decreased with increasing ionic strength, especially for the multivalent salt solutions. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3666–3674, 2004     

Preparation and Gel Properties of Poly[hydroxyethylmethacrylate-co-poly(ethylene glycol) methacrylate] Copolymeric Hydrogels by Photopolymerization

Copolymeric hydrogels based on 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) methacrylate (PEGMA) and isopropanol as a diluent were prepared by photopolymerization. The swelling kinetics, mechanical properties, drug release behaviors, and the interaction between various drugs and the present copolymeric gels were investigated in this study. The results showed that the addition of PEGMA could effectively increase the equilibrium water content and the diffusion coefficient and penetration velocity of water though the gels. Although Young's modulus increased with the increase of PEGMA content, the resulting gels had smaller elongation and more brittle characteristics. The drug release behavior was strongly dependent on the interaction between the present copolymeric gels and drugs such as caffeine, crystal violet (CV), phenol red, and vitamin B₁₂.     

Biocompatible and bioadhesive hydrogels based on 2-hydroxyethyl methacrylate, monofunctional poly(alkylene glycol)s and itaconic acid

Summary Novel poly(Bisomer/HEMA/IA) hydrogels were prepared by radical copolymerization of poly(alkylene glycol) (meth)acrylates, i.e. short chains Bisomers, 2-hydroxyethyl methacrylate (HEMA) and itaconic acid (IA) in a mixture of water/ethanol as solvent. These hydrogels were characterized in terms of swelling in conditions similar to the biological fluids (pH range 2.20–7.40 buffer solutions), compression-strain measurements, thermal properties and morphology. The influence of the type of Bisomer and of the itaconic acid on swelling and mechanical properties, as well as on morphology and thermal behavior of the resulting hydrogels, were investigated. The in vitro study of biocompatibility, carried out with the hydrogels containing different types of Bisomers, showed no evidence of cell toxicity nor any considerable hemolytic activity. All hydrogels showed satisfactory bioadhesive properties, so these materials have potential as drug carriers or biological glue and sealants.     

Novel dually responsive hydrogel with rapid deswelling rate

Hydrogels based on 2‐hydroxyethyl methacrylate (HEMA), methacrylic acid (MAA) and poly(ethylene glycol) methyl ether methacrylate (PEGMA) were prepared by free radical polymerization. The prepared hydrogels were characterized using Fourier transform infrared spectrometry. The states of water in the hydrogels were probed using differential scanning calorimetry and three types of water (free, freezing bound and non‐freezing bound) were detected, the contents of which were calculated. Compared with conventional poly(HEMA‐co‐MAA) hydrogels, the deswelling rate of the poly(HEMA‐co‐PEGMA‐co‐MAA) hydrogels is significantly improved, owing to the introduction of PEGMA. The deswelling process can be well described with a first‐order kinetics equation. Moreover, the swelling ratio of poly(HEMA‐co‐PEGMA‐co‐MAA) hydrogels exhibits a temperature dependence. Based on the analysis of the components of the hydrogels, a brushed core/shell structure is proposed for these, and confirmed by transmission electron microscopy observations. Copyright © 2006 Society of Chemical Industry     

Laser scanning confocal microscopy versus scanning electron microscopy for characterization of polymer morphology: Sample preparation drastically distorts morphologies of poly(2‐hydroxyethyl methacrylate)‐based hydrogels

The internal morphologies for a series of heterogeneous PHEMA and P[HEMA‐co‐MeO‐PEGMA] [PHEMA = poly(2‐hydroxyethyl methacrylate), MeO‐PEGMA = poly(ethylene glycol) methyl ether methacrylate] hydrogels were characterized by scanning electron microscopy (SEM) in conjunction with a sample drying procedure, and by laser scanning confocal microscopy (LSCM) without prior drying. Compared to SEM, LSCM was far simpler and more rapid technique for imaging hydrogels. LSCM also allowed the native hydrated morphology of the hydrogels to be characterized, whereas SEM could only characterize the morphology of samples in their dehydrated state. No dehydration method used in this study preserved the true native morphology, but plunge freezing/freeze drying was the most suitable method that best preserved the native morphology for all hydrogel compositions. Refrigerated freezing/freeze‐drying and critical point drying introduced significant morphological artifacts, the severity of the artifacts being dependant on the sample's composition and Tg. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Poly (2-hydroxyethyl methacrylate)-based hydrogels for slow release of pralidoxime chloride

Pralidoxime chloride (PAM-Cl)-loaded poly (2-hydroxyethyl methacrylate) (PHEMA)-based hydrogels were prepared by bulk copolymerization of 2-hydroxyethyl methacrylate (HEMA) with different mol fractions (0.02–0.10) of trimethylsilyl methacrylate. Characterization of the gels was done by dynamic swelling measurements. It was found that copolymerization does not alter the swelling mechanism of PHEMA and it essentially remains Fickian in nature. In vitro drug-release studies show the increase in release time from 6 to 12 h on incorporation of a 0.1 mol fraction of trimethylsilyl methacrylate on the PHEMA backbone. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 267–270, 1997     

Removal of acidic dye from aqueous solutions using poly(DMAEMA–AMPS–HEMA) terpolymer/MMT nanocomposite hydrogels

In this study, poly(DMAEMA–AMPS–HEMA) terpolymer/montmorillonite nanocomposite hydrogels were prepared by in situ polymerization technique using 2-(N,N-dimethylamino)ethyl methacrylate (DMAEMA), 2-acrylamido-2-methlypropane sulfonic acid (AMPS), 2-hydroxyethyl methacrylate (HEMA) monomers in clay suspension media. N,N-methylenebisacrylamide (NMBA) was used as crosslinker and potassium persulfate/potassium bisulfide were used as initiator and accelerator pair. The water absorption capacities and acidic dye (indigo carmine) adsorption properties of the nanocomposite hydrogels were investigated. Adsorption properties of the hydrogels were investigated at different conditions such as different initial dye concentration and contact time. The concentrations of the dyes were determined using UV/Vis Spectrophotometer at wavelength 610 nm. Langmuir and Freundlich isotherm models were used to describe adsorption data and the results clarified that these models were the best-fit for the adsorption of indigo carmine.     

温度及pH敏感共聚/粘土纳米复合水凝胶的合成与性能研究

以无机粘土为交联剂制备了具有温度、pH双重敏感性的聚（N-异丙基丙烯酰胺-co-甲基丙烯酸-β-羟乙酯）/粘土纳米复合水凝胶（P（NIPA-co-HEMA）/clay）,并用红外和X衍射对其结构和形态进行了表征。在弱碱性（pH=7.4）和25℃条件下,分别研究了温度和不同pH缓冲溶液对该凝胶溶胀度的影响,测定了纳米复合水凝胶的力学性能。结果表明：水凝胶的粘土已被剥离成单片层,且均匀分散在凝胶网络中,起交联作用;P（NIPA-co-HEMA）/clay具有良好的温度、pH双重敏感特性;凝胶的断裂伸长率〉1000%。     

Poly[2-(hydroxyethyl methacrylate)-co-(sulfobetaine)]s hydrogels: 1. Synthesis and swelling behaviors of the 2-(hydroxyethyl methacrylate)-co-2-(vinyl-1-pyridinium propane sulfonate) hydrogels

A series of the 2-hydroxyethyl methacrylate/2-vinyl-l-pyridinium propane sulfonate (HEMA/VPPS) copolymeric gels have been prepared from HEMA and zwitterionic monomer VPPS of various molar ratios. The influence of the amount of VPPS in copolymeric gels on their swelling behavior in water and various saline solutions at different temperatures was investigated. Results indicate that the PHEMA hydrogels exhibit an overshooting phenomenon in their dynamic swelling behavior. The maximum overshooting value decreases with increasing temperature. The same results are also shown for the lower VPPS content HEMA/VPPS copolymeric gels. In the equilibrium swelling ratio, the PHEMA hydrogel exhibits a minimum swelling ratio at 55 °C. Then, the minimum swelling ratio disappears gradually with increasing VPPS content in HEMA/VPPS copolymeric gels. In the saline solution, the swelling ratios of HEMA/VPPS copolymeric gels increase rapidly with increasing salt concentration, for salts with a smaller ratio of charge/radius.     

pH‐reversible hydrogels. IV. Swelling behavior of the 2‐hydroxyethyl methacrylate‐co‐acrylic acid‐co‐sodium acrylate copolymeric hydrogels

A series of 2‐hydroxyethyl methacrylate (HEMA) and sodium acrylate (SA50) copolymeric gels were prepared from HEMA and the anionic monomer SA50 with various molar ratios. The influence of SA50 on the copolymeric gels on their swelling behavior in deionized water at different temperatures and various pH buffer solutions was investigated. Results indicated that the poly(2‐hydroxyethyl methacrylate) (PHEMA) hydrogels exhibited an overshooting phenomenon in their dynamic swelling behavior. The maximum overshooting value decreased with increasing of the temperature. The same results were also found in the HEMA/SA50 copolymeric gels with a lower SA50 content. On the contrary, the overshooting phenomenon for HEMA/SA50 copolymeric gels with a higher content of SA50 was exhibited only under higher temperature (over 35°C). These copolymer gels were used to assess drug release and drug delivery in this article. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 81: 1360–1371, 2001     

Comparing emulsion polymerization of methacrylate-monomers with different hydrophilicity

A comprehensive experimental study concerning the influence of various types of initiator-emulsifier systems on emulsion polymerization of methacrylate monomers (2-hydroxyethyl methacrylate (HEMA), methyl methacrylate (MMA) and butyl methacrylate (BMA)) reveals interesting relations between initiator and surfactant hydrophilicity on the one hand and the hydrophilicity of the monomers on the other hand. For the water-soluble HEMA stable latexes are only obtained if hydrophobic initiators such as 2,2′-azobisisobutyronitrile or dibenzoyl peroxide in combination with alkyl sulfate surfactants with carbon chain lengths greater than 10 or surface active initiators of the 2,2′-azobis(N-2′-methylpropanoyl-2-amino-alkyl-1)-sulfonate type with alkyl chain lengths greater than 8 are employed. Stable nano size range poly(2-hydroxyethyl methacrylate) (PHEMA) particles have been prepared also by batch emulsion polymerization using ionic surface active initiators (inisurfs). The results clearly show that the formation of stable latex particles requires a proper choice of the initiator-emulsifier system regarding its hydrophilic-hydrophobic balance. The PHEMA particles prepared with surface-active initiators keep their identity and spherical shape even in the dried state whereas in the case of the other initiator-emulsifier systems complete coagulation and coalescence occurs during drying.     

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     

Superabsorbent polymeric materials. XIII. Effect of oxyethylene chain length on water absorbency for the sodium acrylate and poly(ethylene glycol) methyl ether acrylate (PEGMEAn) copolymeric gels

In a previous study, we prepared a series of xerogels based on sodium acrylate (NaA) and 2‐hydroxyethyl methacrylate (HEMA, OE = 1) or poly(ethylene glycol) methacrylate (PEGMA, OE = 6) with different oxyethylene (OE) units. The effect of the contents of HEMA and PEGMA in the copolymeric gel on the swelling behavior in deionized water and various saline solutions was studied. Their results showed that the water absorbencies for these two series gels were effectively improved by adding a small amount of HEMA or PEGMA. In this article, a series of novel xerogels based on NaA and hydrophilic monomer poly(ethylene glycol) methyl ether acrylate (PEGMEA_n), which was synthesized from acryloyl chloride and poly(ethylene glycol) monomethyl ether with three oxyethylene (OE = 9, 16, 45) chain lengths, were prepared by inverse suspension polymerization. The effects of OE chain length in the copolymeric gel on the water absorption behavior and initial absorption rate for the present xerogels were investigated. Results showed that adding a small amount of PEGMEA_n could effectively increase the water absorbency of the gels. In addition, the water absorbency decreased with an increase of the OE chain length in PEGMEA_n. The initial absorption rate for the present copolymeric gels increased with increasing OE chain length in PEGMEA_n and the content of PEGMEA_n in the copolymeric gels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 927–934, 2006     

Synthesis of uniform microspheres with higher content of 2-hydroxyethyl methacrylate by employing SPG (Shirasu porous glass) emulsification technique followed by swelling process of droplets

Relatively uniform microspheres containing a hydrophilic monomer, 2-hydroxyethyl methacrylate (HEMA), were prepared by employing a swelling method of uniform seed droplets. A uniform seed emulsion composed mainly of styrene (St) was prepared by the Shirasu porous glass (SPG) membrane emulsification technique; this was mixed with a secondary emulsion composed mainly of HEMA/St or HEMA/MMA (methyl methacrylate) prepared by a homogenizer for swelling. The swollen droplets obtained were polymerized at 75°C under a nitrogen atmosphere. The uniform microsphere with a higher content of HEMA was obtained successfully by the swelling method while it failed by a direct emulsification method. The effects of the composition of the oil phase and the inhibitor in the continuous phase on the incorporated fraction of HEMA, the morphology of particles, and monomer conversion were investigated. It was found that the incorporated fraction of HEMA increased with increasing its feed fraction, and more HEMA was incorporated into the microsphere when HEMA/MMA was used as the oil phase of the secondary emulsion rather than HEMA/St. Although the final conversion was very low when the feed fraction of HEMA was higher, it can be increased to more than 80% by using an adequate amount of ethylene glycol dimethacrylate (EGDMA) as a crosslinker and NaNO₂ as an inhibitor in the aqueous phase. Various microspheres with different morphologies such as spherical, snowmanlike, and popcornlike were observed, depending on composition of the oil phase. Furthermore, the porous microsphere with a high content of HEMA was obtained by employing hexanol (HA) as a porogen. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 1325–1341, 1997     

Characterization and In Vitro Drug Release Behavior of (2-hydroxyethyl methacrylate)–co-(2-acrylamido-2-methyl-1-propanesulfonic acid) Crosslinked Hydrogels Prepared by Ionizing Radiation

A series of copolymer hydrogels of 2-hydroxyethyl methacrylate (HEMA)/2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) were prepared by solution free radical polymerization using gamma irradiation. Fourier transform infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy techniques were used to characterize the HEMA/AMPS hydrogels. The swelling behavior of the prepared hydrogels was determined by investigating the time and pH-dependent swelling of the HEMA/AMPS hydrogels of different AMPS content. The drug loading and controlled release behaviors of the hydrogel were evaluated using hydrocortisone acetate as drug model. The results indicated that the release rate of the drug from the hydrogel showed good pH-response.     

水在凝胶中的存在状态及其对凝胶力学性能的影响

以偶氮二异丁腈为引发剂,通过化学引发聚合合成甲基丙烯酸β-羟乙酯（HEMA）/N-乙烯基吡咯烷酮（NVP）二元共聚物和HEMA /NVP /甲基丙烯酸甲酯（或甲基丙烯酸丁酯）三元共聚物水凝胶,通过示差扫描量热法（DSC）结合热重法（TG）研究了不同单体配比的共聚物水凝胶中水的状态,证明了凝胶中存在3种不同状态的水：非冻结结合水、可冻结结合水和可冻结自由水.结果发现可冻结水的含量主要由NVP含量所决定,NVP单元基本不能键合水,而非冻结水的含量主要受HEMA含量和疏水性单体甲基丙烯酸酯含量影响.疏水性单体的引入使材料的力学强度提高,对凝胶体系具有增塑作用的是非冻结水而不是可冻结的结合水和自由水.     

Ion-stimuli responsive dimethylaminoethyl methacrylate/hydroxyethyl methacrylate copolymeric hydrogels: mutual influence of reaction parameters on the swelling and mechanical strength

Novel ion-stimulus-responsive copolymeric hydrogels were synthesized by free radical crosslinking copolymerization from the monomers N,N-dimethylaminoethyl methacrylate (DMAEMA) and 2-Hydroxyethyl methacrylate (HEMA) in the presence of a crosslinker, diethyleneglycol dimethacrylate (DEGDMA). The influences of the reaction parameters, the comonomer composition and the ionic strength of salt solutions on the swelling behavior of P(DMAEMA-co-HEMA) hydrogels were examined. The ion-stimulus-responsive swelling behavior of the prepared copolymers was studied in water as well as in aqueous solutions of NaCl, KCl, KBr, KI, CaCl₂, BaCl₂ and MgCl₂. It was found that, starting from some characteristic concentration of a salt, a further increase of the salt concentration results in the shrinking of copolymeric P(DMAEMA-co-HEMA) hydrogels. The Flory-Rehner theory correctly predicts the swelling behavior of the hydrogels in salt solutions if the variation of the comonomer HEMA content is taken into account. The calculation of the interaction parameter χ between P(DMAEMA-co-HEMA) network and water showed that the specific interactions between cations and side groups of polymeric network affect the mixing term of the free energy. The extent and kinetics of water absorption were studied to determine their relationship with the reaction parameters. The kinetics of the hydrogel collapse is strongly dependent on the kind of salt used. The swelling results will be useful in designing and developing novel controlled delivery systems.     

Novel polyurethane hydrogels for biomedical applications

Polyurethane hydrogels derived from UV-curable urethane prepolymer and hydrophilic monomers were prepared and their properties were evaluated. The urethane prepolymer used in this study contained well-defined hard segments centered with a polyether-based soft segment and end-capped with methacrylate groups. The hydrophilic monomers studied were 2-hydroxyethyl methacrylate (HEMA), N-vinyl pyrrolidone, and glycerol methacrylate. Methacryloxypropyl tris (trimethysiloxy) silane (TRIS) was also used in some cases to modify properties. All composition were UV-cured and formed hydrogels after hydration. The oxygen permeabilities of the hydrogels decreased as the water contents increased and increased as the TRIS content was increased. The tear strengths and moduli decreased as the water contents of the hydrogels increased. Most compositions studied have higher oxygen permeability and tear strength than poly(HEMA) because of the presence of urethane prepolymer in the composition.     

Preparation and properties of modified PHEMA hydrogel with sulfonated PEG graft

A novel poly(ethylene glycol) (PEG) macromer with a methacryloyl and sulfonic acid group at each end of the chain was prepared. Modified hydroxyethyl methacrylate (HEMA) based hydrogels were synthesized by crosslinking polymerization of HEMA in the presence of the above‐mentioned PEG macromer. The effect of the sulfonated PEG graft was examined by comparing the swelling properties with those of a pure poly(hydroxyethyl methacrylate) (PHEMA) hydrogel. The modified PHEMA hydrogel exhibited increasing water absorbency with increasing sulfonated PEG content up to 15 wt %. These hydrogels with the sulfonated PEG graft exhibited a more hydrophilic character than the pure PHEMA gel. Also the swelling degree varied slightly with pH, showing increased swelling at higher pH probably due to the presence of the anionic sulfonate group on the PEG end chain. In addition, the protein adsorption test showed a lower level of fibrinogen adsorption from the sulfonated poly(ethylene glycol) (SPEG) modified gel than on the homo PHEMA hydrogel. Interestingly, scanning electron microscopy showed that the porous and rather uniform morphology of the gels changed with increasing sulfonated PEG content in PHEMA. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 2484–2489, 2007     

Multifunctional sensors based on silicone hydrogel and their responses to solvents,pH and solution composition

In this paper, multicomponent silicone hydrogels were prepared by the copolymerization of the hydrophobic silicon‐containing monomer bis(trimethylsilyloxy) methylsilylpropyl glycerol methacrylate with two hydrophilic monomers 2‐hydroxyethyl methacrylate and N‐vinyl pyrrolidone. The response of the silicone hydrogels to different stimuli was evaluated by observing the swelling ratios of the hydrogels. The results show that the hydrogels display different responses to variations in pH and solvent. Multifunctional sensors were then prepared based on the silicone hydrogels to detect the pH value of solutions, the types of solvent and the ethanol percentage in water. The results could be obtained by visual inspection and the sensors were reusable. © 2016 Society of Chemical Industry