pH响应PAAm-g-PEG/PVP半互穿网络水凝胶的制备以及溶胀动力学

采用硝酸铈胺-聚乙二醇为氧化-还原引发体系,N,N-亚甲基双丙烯酰(N,N-MBA)为交联剂,通过简单的自由基聚合法,设计合成了一种聚(丙烯酰胺-g-聚乙二醇)/聚乙烯吡咯烷酮PAAm-g-PEG/PVP接枝交联结构的半互穿网络水凝胶。研究了它们在不同pH值缓冲溶液中的溶胀与扩散行为以及溶胀动力学;并采用红外光谱和热分析系统对其结构和热性能进行了分析测量。实验结果表明:水凝胶的溶胀行为和扩散模式取决于溶液的pH值。随着缓冲溶液pH值增加,平衡溶胀率减小;在不同的缓冲溶液中理论最大吸水量S∞与实验值基本相一致。水凝胶的溶胀行为可以通过选择加入不同分子量大小的PEG来调节和控制。     

Thermal and swelling studies of hydrophobically modified polyacrylamide hydrogels

Hydrophobically modified polyacrylamide hydrogels were prepared by polymerizing acrylamide, using n‐butyl acrylate and 2‐ethyl hexyl acrylate as comonomers and dimethyl formamide as a solvent. We report here for the first time that the Alfred Q‐e reactivity ratios are matching with the experimental value (elemental analysis result) for the terpolymer hydrogel systems. Differential scanning calorimetry (DSC) thermograms of the hydrogel samples revealed two endothermic transitions, one near 0°C, corresponding to the melting transition of ice and another above ambient temperature. This high temperature transition is due to the rearrangement of water molecules engaged in hydrophobic hydration surrounding the hydrophobic groups (alkyl side chains). This depends on the type of hydrophobic groups and the gel compositions. Swelling and deswelling studies of the gels were performed using various solvents such as water and isopropyl alcohol. An abnormally high swelling and deswelling behavior was observed in the homopolymer gels and the gels with low amount of hydrophobic comonomers. This could be attributed to the more intramolecular cross‐linked structure formed during synthesis in organic solvent. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Preparation and swelling behavior of macroporous poly(acrylamide‐co‐sodium methacrylate) superabsorbent hydrogels

Macroporous superabsorbent hydrogels (SAHs) composed of acrylamide (AAm) and sodium methacrylate (NMA) were prepared by aqueous solution polymerization in the presence of a glucose solution. Their swelling capacity was investigated as a function of the concentrations of the glucose solution, sodium methacrylate, crosslinker, initiator, and activator. The porosity of the poly(acrylamide‐co‐sodium methacrylate) superabsorbent hydrogels was confirmed using scanning electron microscopy. The SAHs were characterized by IR spectroscopy. To estimate the effect on the swelling behavior, three types of crosslinkers were employed: N,N′‐methylenebisacrylamide, 1,4‐butanediol diacrylate, and diallyl phthalate. Network structural parameters such as initial swelling rate, swelling rate constant, and maximum equilibrium swelling were evaluated by water absorption measurement. The equilibrium water content (EWC%) of the AAm–NMA macroporous SAHs was found to be in the range of 93.31–99.68, indicating that these SAHs may have applications as biomaterials in the medicinal, pharmaceutical, and veterinary fields. Most of the SAHs prepared in this investigation followed non‐Fickian‐type diffusion, and few followed a case II– or super–case II‐type diffusion. The diffusion coefficients of these macroporous SAHs were investigated. Further, the swelling behavior of these SAHs also was investigated at different pHs and in different salt solutions and simulated biological fluids. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 3202–3214, 2006     

Preparation and swelling characterization of poly (n‐isopropylacrylamide)‐based porous hydrogels

Nine different poly(n‐isopropylacrylamide)‐based hydrogels, including nonionic, cationic, and anionic hydrogels, were synthesized in with and without the addition of pore‐forming agents. The synthesized hydrogels were characterized with dry gel density measurements, scanning electron microscopy observations, and the determination of the swelling ratio swelling kinetics. All the results showed that the cationic hydrogels had faster swelling kinetics than the anionic and nonionic hydrogels. The addition of pore‐forming agents (NaHCO₃ and carboxymethylcellulose) during the synthesis process led to porous hydrogels with lower dry densities, swelling ratios, and swelling kinetic parameter values. An empirical equation was developed to successfully correlate the swelling kinetic parameter with the hydrogel swelling ratio. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 3651–3658, 2004     

Preparation of polyacrylamide hydrogels at various charge densities by postmodification

In this study, first polyacrylamide hydrogels were synthesized by free‐radical crosslinking polymerization of acrylamide monomer with N,N′‐methylenebis(acrylamide) as a crosslinker in an aqueous solution at 22°C. Then, a series of hydrogels at various charge densities were prepared by partial hydrolysis of polyacrylamide precursors in a 0.1M sodium hydroxide solution at 60°C. The hydrolysis time was varied between 20 and 180 min. The chemical structures and internal morphologies of the hydrogels before and after alkaline hydrolysis were characterized with attenuated total reflectance/Fourier transform infrared and scanning electron microscopy measurements. The swelling ratio of the hydrolyzed hydrogels was measured in buffer solutions at various pHs. From differential curves of dQ_v/dpH versus pH (where Q_v is the equilibrium swelling ratio of the hydrogels), the volume phase transition pH of the hydrogels was found to be 4.33 ± 0.05, regardless of the charge density of the hydrogels. In water at 22°C, the hydrogels with greater charge density showed a more rapid swelling rate because of their higher porosity and hydrophilicity. Moreover, in buffer solutions with the pH changing from 9.0 to 2.0 at 22°C, the hydrogels with greater charge density also exhibited a more rapid deswelling rate than the hydrogels with less charge density. In conclusion, the postmodification method is a good way of preparing pH‐sensitive hydrogels with fast responsiveness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Equilibrium swelling behavior and elastic properties of polymer–clay nanocomposite hydrogels

Nanocomposite hydrogels were prepared by free‐radical polymerization of the monomers acrylamide (AAm), N,N‐dimethylacrylamide (DMA), and N‐isopropylacrylamide (NIPA) in aqueous clay dispersions at 21°C. Laponite XLS was used as clay nanoparticles in the hydrogel preparation. The hydrogels based on DMA or NIPA monomers exhibit much larger moduli of elasticity compared with the hydrogels based on AAm monomer. Calculations using the theory of rubber elasticity reveal that, in DMA‐clay or NIPA‐clay nanocomposites, both the effective crosslink density of the hydrogels and the functionality of the clay particles rapidly increase with increasing amount of Laponite up to 10% (w/v). The results suggest that DMA‐clay and NIPA‐clay attractive interactions are stronger than AAm‐clay interactions due to the formation of multiple layers on the nanoparticles through hydrophobic associations. It was also shown that, although the nanocomposite hydrogels do not dissolve in good solvents such as water, they dissolve in dilute aqueous solutions of acetone or poly(ethylene oxide) of molecular weight 10,000 g/mol, demonstrating the physical nature of the crosslink points. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Stiffness xanthan hydrogels: synthesis,swelling characteristics and controlled release properties

Summary  New xanthan hydrogels were synthesized at 90 C in water acid media using adipic acid dihydrazide (ADH) as crosslinking agent, in the presence of 1-ethyl-3[3-dimethyl amino] propyl carbodiimide hydrochloride (EDCI) as reagent. In these conditions, xanthan chains are in a predominantly helical conformation and through rheological measurements the influence of the temperature over the helix-coil transition was assessed. Xanthan hydrogels with different concentration in polysaccharide and ADH were obtained and characterised by elemental analysis and swelling properties. High concentration of xanthan (i.e. 25gL^-1) is needed to obtain gel due to the low available carboxylic functions in the helical conformation. During the swelling analysis, it was noted that high temperature (i.e. 90 C) favoured the conformational transitions within the network. The drug loading and releasing properties were estimated using methylene blue as model molecule and different experimental pH and ionic strength conditions.     

Preparation and properties of transparent cellulose hydrogels

Highly transparent cellulose hydrogels with physical crosslinkage were prepared from nonaqueous organic cellulose solutions and viscose by coagulating and regenerating cellulose in an aqueous solution containing a water‐miscible organic solvent. Nonaqueous organic cellulose solutions used were LiCl/dimethylacetamide, paraformaldehyde/dimethyl sulfoxide, and triethylammonium chloride/dimethyl sulfoxide. Preparation conditions and physical properties of the transparent cellulose hydrogels were studied. The transparency of the cellulose hydrogels depended on the composition of the aqueous solution containing the organic solvent. Furthermore, transparent cellulose hydrogels from viscose showed high tensile strength. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 3020–3025, 2003     

Equilibrium swelling studies of highly swollen acrylamide/mesaconic acid hydrogels

Acrylamide/mesaconic acid (AAm/MA) hydrogels were prepared by free radical solution polymerization in aqueous solution of acrylamide (AAm) with mesaconic acid (MA) as comonomer and two multifunctional crosslinkers such as ethylene glycol dimethacrylate (EGDMA) and 1,4‐butanediol dimethacrylate (BDMA). Swelling experiments were performed in water at 25°C, gravimetrically. The influence of mesaconic acid content in hydrogels was examined. Swelling of AAm/MA hydrogels was increased up to 2301% (for containing 20 mg MA and crosslinked by EGDMA) to 3296% (for containing 80 mg MA and crosslinked by BDMA), while AAm hydrogels swelled up to 1330% (crosslinked by BDMA) to 1400% (crosslinked by EGDMA). The values of equilibrium water content of the hydrogels are 0.9301–0.9706. Diffusion behavior was investigated. Water diffusion into hydrogels was found to be non‐Fickian in character. Diffusion coefficients of AAm/MA hydrogels were calculated by the short time approximation and found to be from 38.01 × 10^?6 cm² s^?1 to 182.73 × 10^?6 cm² s^?1. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2253–2259, 2005     

Discrimination of the roles of crosslinking density and morphology in the swelling behavior of crosslinked polymers: Poly(N‐vinylimidazole) hydrogels

The degree of swelling (S) of crosslinked polymers depends on several variables whose individual contributions are difficult to be distinguished. The aim of this work is to determine the contributions of the morphology to S, discriminating them from the effect of the crosslinking density. Under usual conditions of synthesis, these two characteristics vary simultaneously but here, several samples of chemically crosslinked poly(N‐vinylimidazole) having the same permanent crosslinking density (determined by DSC) and different porous morphologies (determined by SEM) were prepared. It was thus found that the variation of S with porosity, keeping constant the rest of variables, is strongly solvent dependent. Swelling in methanol is almost constant whereas for ethanol, deionized water, and aqueous HCl solutions, S depends on morphological features in a different way for each medium. It was concluded that S increases with inherent porosity and solvent effects arise from the counterbalance of such increment with the dependence of the polymer‐solvent interaction parameter on the polymer volume fraction. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Behavior of acrylic acid–itaconic acid hydrogels in swelling,shrinking, and uptakes of some metal ions from aqueous solution

An experimental research of the absorption properties of metal ions onto synthetic hydrogel obtained by solution polymerization of acrylic acid and itaconic acid in presence of N,N′‐methylenebisacrylamide as crosslinking agent was carried out. The swelling behavior in aqueous salt solutions was studied as a function of divalent cation concentration (Cu²⁺, Zn²⁺, Ni²⁺, Co²⁺, Cd²⁺, Pb²⁺, Hg²⁺) in the external solution ranging from 10^?5 to 1M, at 25°C. The ability of these hydrogels to bind cations was measured at different pH values and metal ion concentrations. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 90: 530–536, 2003     

Synthesis and characterization of polyelectrolyte hydrogels with controlled swelling behaviour

Copolymerization of sulfopropyl methacrylate potassium salt (K‐SPMA) and 2‐acrylamido‐2‐methyl propane sulfonic acid (AMPS) has been studied in the range 10–90% K‐SPMA in the feedstock. The reactivity ratios have been determined for K‐SPMA/AMPS copolymers. The copolymer compositions, utilized for determining the reactivity ratio, have been determined from nitrogen content. Crosslinked poly(AMPS) and K‐SPMA/AMPS copolymers were prepared in water in the presence of potassium persulfate as initiator and N,N‐methylene bisacrylamide (MBA) as tetrafunctional crosslinker. Irradiation of K‐SPMA and AMPS with an electron‐beam was carried out at 50 wt% aqueous solution with low pH and irradiation dose 40–120 kGy. The swelling behaviour of highly crosslinked K‐SPMA/AMPS copolymer polyelectrolyte gels in aqueous medium was studied in the presence of different types of salts. The crosslink density, the average molecular weight between the crosslinks and the dissociation constant (pK_a) of the crosslinked polymer were determined from stress–strain measurements. © 2001 Society of Chemical Industry     

聚苯胺/碳纳米管杂合水凝胶的合成及膨胀性能研究

合成了一种以甲基丙烯酸-丙烯酰胺共聚网络P(AAm-co-MAA)为基体,以聚苯胺为互穿组分(PANI)的半互穿网络杂合水凝胶。研究表明,当将PANI和MWNTs-COOH被引入到P(AAm-co-MAA)网络中后得到的P(AAm-co-MAA)/PANI/MWCNT-COOH半互穿网络杂合水凝胶则能保持较好的膨胀性,同时发现,依靠调节PA-NI/MWNTs-COOH的含量可以使杂合水凝胶膨胀性增加。这为研究杂合水凝胶的力学性能和pH敏感性提供了一个窗口。     

Determination of crosslinking density of hydrogels prepared from microcrystalline cellulose

Hydrogels with four different plant‐based microcrystalline cellulose concentrations were prepared using the self‐assembly technique. The interaction parameter between cellulose and water was determined by the classical Flory‐Huggins theory, and was found to be around 0.44 with weak concentration dependence. The crosslinking density in these hydrogels was measured by both the Mooney‐Rivlin equation and the Flory‐Rehner theory. Reasonable consistency was found between the two methods albeit results from the Flory‐Rehner theory were slightly higher due to the contribution from the physical crosslinks. The crosslinking density values for all four hydrogels determined from both methods were found to range from 19 to 56 mol/m³. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

亲水-疏水PVP-semi-IPN-PCL水凝胶的制备与溶胀性能

N-乙烯基吡咯烷酮（NVP）在聚己内酯（PCL）的乙酸乙酯溶液中进行自由基聚合,制备了亲水-疏水性聚乙烯吡咯烷酮（PVP）/聚己内酯（PCL）半互穿网络水凝胶（PVP-semi-IPN-PCL）。凝胶中PCL的熔融温度T_m无明显变化,而T_m吸热峰形状随PVP含量变化。凝胶平衡溶胀率（ESR）随PVP含量的升高而增大,结合水量的增大尤其显著。由于“笼蔽效应”,低浓度引发剂时,偶氮二异丁睛（AIBN）引发制备的凝胶ESR低于过氧化苯甲酰（BPO）引发剂。交联剂浓度较低时,以戊二醛交联形成凝胶的ESR较N,N-亚甲基双丙烯酰胺（NMBA）交联形成的凝胶大。浓度较高时,戊二醛交联凝胶ESR较NMBA低。PVP含量（质量）分别为20%、40%、60%、80%时,凝胶溶胀动力学Fick模型中的n值分别为0.854、0.471、0.466、0.253,说明在合适的PVP含量时,凝胶的溶胀动力学符合Fick模型。     

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     

Novel hydrogels of PVP–CMC and their swelling effect on viscoelastic properties

Polyvinylpyrrolidone (PVP) and carboxymethyl cellulose (CMC) mixed hydrogels were prepared by heat treatment. The physical characteristics of the hydrogels were studied by Fourier transform infrared spectroscopy and scanning electron microscopy. The swelling study of the hydrogels in water shows remarkable water absorption property. The swelling effect on the rheological behavior of PVP‐, PVP–CMC‐, and CMC‐based hydrogels was investigated to judge its application on uneven surface of body. The rheological properties (storage modulus, loss modulus, and complex viscosity) of samples before drying and swelled (15, 30, and 60 min) were measured against angular frequency and composition. The hydrogel containing PVP/CMC ratio of 20 : 80 appeared to be the best hydrogel from rheological and water absorbent points of view. These properties and low cost of the materials utilized in this work suggest that this hydrogel is a viable alternative product for dressing materials. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

Structural aspects and nature of swelling medium as equilibrium swelling determinants of acrylamide and cellulosic‐based smart hydrogels

Hydroxypropylcellulose (HPC)‐based interpenetrating networks (IPN) with acrylamide (AAm) were synthesized in aqueous medium by simultaneous γ‐ray initiation in the presence of N,N‐methylenebisacrylamide (N,N‐MBAAm). The effect of the synthetic reaction conditions was evaluated for optimum network yield and networks of cellulose and some of its derivatives were obtained with AAm by using these conditions. FTIR, elemental analysis, and scanning electron micrography (SEM) for various structural aspects have characterized networks. Apart from kinetics of IPN formation, this article discusses swelling response of these novel hydrogels in different swelling media. Swelling behavior was studied as a function of synthetic reaction conditions, structure of cellulosics used, and nature of swelling medium (water, 0.5N NaOH, 0.5N HCl, and 5% NaCl). Equilibrium swelling was observed to depend on both structural and environmental factors. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 85: 1161–1169, 2002     

Dynamic and equilibrium swelling studies: crosslinked pH sensitive methyl methacrylate-co-itaconic acid (MMA-co-IA) hydrogels

In the present work crosslinked methyl methacrylate-co-itaconic acid (MMA-co-IA) hydrogels were prepared by free radical copolymerization of methyl methacrylate (MMA) with itaconic acid (IA) using ethylene glycol dimethacrylate (EGDMA) and N, N methylene bisacrylamide (MBAAm) as crosslinkers and benzoyl peroxide as initiator. Prepared hydrogels were investigated for dynamic and equilibrium swelling studies. For swelling behaviour, effect of pH, monomeric compositions, degree of crosslinking and type of crosslinking agent were investigated. Swelling studies were performed in the USP phosphate buffer solutions of varying pH 1.2, 4.5, 5.5, 6.5 and 7.0. Results showed that swelling increased by increasing IA content in hydrogels structure. This may be due to the presence of more carboxylic groups available for ionization. Swelling was decreased with increase in crosslinking ratio owing to tighter hydrogel structure. Hydrogels were characterized by Fourier transform infrared (FTIR), and scanning electron microscope (SEM). Polymer-solvent interaction parameters (χ) of hydrogels were determined by using Flory–Rehner theory of equilibrium swelling values. The analysis of diffusion mechanism from gels using Peppas model showed that all monomeric compositions and degrees of crosslinking followed Fickian diffusion.     

FTIR-ATR measurements of the ionization extent of acrylic acid within copolymerized methacrylated dextran/acrylic acid networks and its relation with pH/salt concentration-induced equilibrium swelling

In this study, dextran hydrogels were obtained by free radical copolymerization of methacrylated dextran with acrylic acid (AAc) in aqueous solution. The fractions of dissociation of AAc units within hydrogel in response to changes in pH and ionic strength of external aqueous solution were determined by FTIR-ATR spectroscopy. The influence of small ion concentration within hydrogel on the dissociation constant of AAc follows the Debye-Hückel behavior. Based on the results from the FTIR-ATR measurements, the total ion concentration difference inside and outside the hydrogel was determined according to the Donnan equilibrium theory, taking account of the counterion condensation effect quantitatively. The swelling response of hydrogels to changes in external pH and ionic strength was governed mainly by the ionic osmotic pressure due to the accumulation of diffusible ions within hydrogels. The energy balance between the osmotic and elastic retractile responses indicates the non-Gaussian behavior of elastically effective subchains with increasing swelling.