Rapid pH‐dependent phase transition and elasticity of stimuli‐responsive cationic poly(N,N‐dimethylaminoethyl methacrylate) hydrogels prepared with a dimethacrylate crosslinker

Stimuli‐responsive hydrogels prepared from poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) and its copolymers have attracted much interest to serve in biomedical and pharmaceutical applications. To investigate pH‐dependent swelling and elasticity, a series of cationic hydrogels based on N,N‐dimethylaminoethyl methacrylate were prepared by free radical crosslinking copolymerization at 60 °C in the presence of tetraethylene glycol dimethacrylate as the crosslinker. The equilibrium swelling and the mechanical properties of the PDMAEMA hydrogels were investigated as a function of the gel preparation concentration. To explain the effect of pH on the equilibrium swelling of the hydrogels, pH‐dependent swelling studies were carried out in solutions of pH ranging from 2.1 to 10.7. It was found that the PDMAEMA hydrogels exhibit a rapid pH‐dependent phase transition in aqueous solutions; that is, the gels first remain in the swollen state at acidic pH then collapse in a very narrow range of pH. The results showed that the volume of PDMAEMA hydrogels in acidic conditions is about 10‐ to 40‐fold larger than that in the basic pH region. By using the Flory–Rehner theory, the characteristic network parameters of the PDMAEMA hydrogels were calculated and good agreement obtained between the swelling equilibria of hydrogels and their mechanical properties over the whole range of gel preparation concentration. © 2012 Society of Chemical Industry     

Positively charged composite nanofiltration membrane prepared by poly(N,N‐dimethylaminoethyl methacrylate)/polysulfone

Poly(N,N‐dimethylaminoethyl methacrylate) (PDMAEMA) can be crosslinked by quaternization to develop a positively charged dense network structure. According to this mechanism, PDMAEMA/polysulfone (PSF) positively charged nanofiltration membrane was developed by interfacial crosslinking polymerization using PSF plate microfiltration membrane as support layer, PDMAEMA aqueous solution as coating solution, and p‐xylylene dichloride/n‐heptane as crosslinking agent. Technique and condition of developing membrane such as concentration of coating solution, coating time, pH value of coating solution, content of low molecular weight additive in coating solution, concentration of crosslinking agent, crosslinking time, and number of coatings were studied. FTIR, SEM, and X‐ray photoelectron spectroscopy were used to characterize the structure of membranes. This membrane had rejection to inorganic salts in water solution, the rejection rate to MgSO₄ (1 g/L water solution at 0.8 MPa and 30°C) was about 90%, and permeation flux was about 10–20 L m^?2 h^?1. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 2721–2728, 2004     

Synthesis and characterization of hybrid clay/poly (N,N‐dimethylaminoethyl methacrylate) nanocomposites

Four quaternary ammonium salt monomers (2a–d) were synthesized from N,N‐dimethylaminoethyl methacrylate and subsequently polymerized to afford cationic polymers (3a–d). The synthesized monomers and polymers were characterized by Fourier transform infrared (FTIR) and proton nuclear magnetic resonance (¹H NMR) spectroscopy. Molecular weights of the synthesized polymers were determined using gel permeation chromatography. Polymer/clay nanocomposites (4a–d) were prepared using solution‐intercalation method and characterized by FTIR, X‐ray diffraction, high‐resolution transmission electron microscopy, energy dispersive X‐ray, and thermogravimetric analysis. Data analysis showed that polymer/clay nanocomposites have intercalated structure. The dielectric properties of the polymer/clay nanocomposites were studied as a function of both temperature and frequency. POLYM. COMPOS., 37:2950–2959, 2016. © 2015 Society of Plastics Engineers     

pH‐sensitive dimethylaminoethyl methacrylate (DMAEMA)/acrylamide (AAm) hydrogels: Synthesis and adsorption from uranyl acetate solutions

A random copolymer of dimethylaminoethyl methacrylate (DMAEMA) and acrylamide(AAm) [poly(DMAEMA/AAm)], with a pH‐sensitive character, was prepared by a redox polymerization method. Increasing the DMAEMA content of the gel, the pH, and the ionic strength of the solution decreased the swelling ratios of the hydrogels. The adsorption of poly(DMAEMA/AAm) hydrogels from uranyl acetate (UA) solutions was studied at different pHs. The adsorption capacity of hydrogels increased from 200 to 1200 mg of UA per gram of dry hydrogel with increasing pH of the adsorption solution. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2028–2031, 2003     

Overshooting effect of poly(dimethylaminoethyl methacrylate) hydrogels

An overshooting effect was observed during the swelling procedure of poly(dimethylaminoethyl methacrylate) (PDMAEMA) gel for the first time. The effects of the temperature, ionic strength, and pH on the overshooting effect of the PDMAEMA gel were investigated. We found that the overshooting effect of the gel could not be eliminated by changing the temperature; however, the overshooting effect was indiscernible in high‐concentration NaCl solutions (>0.2 mol/L) and basic (pH 11.9) and acidic solutions (pH = 2.1). The overshooting effect of the PDMAEMA gel was attributed to the dynamic conformational changes of the side chains of dimethylaminoethyl methacrylate (DMAEMA) units during the swelling of the gels. In the presence of NaCl or NaOH, the stretching of the macromolecular chains of the gels was disrupted. While in acidic solution, the protonation of tertiary amino groups in the DMAEMA units made the side chains of the DMAEMA units change from the cyclic conformation to the stretched one; this was analyzed with the aid of Fourier transform infrared spectroscopy. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation of poly (N,N‐dimethylaminoethyl methacrylate) (PDAEM) membranes: Application for water purification

The present work concerns a development of new membranes for performing ions separation. These membranes were prepared by solution casting followed by solvent evaporation, using a commercial cellulose triacetate (CTA), synthesized poly (N,N‐dimethylaminoethyl methacrylate), macrocylic polyethers (15‐crown‐5 and Dibenzo‐24‐crown‐8) as carrier and dioctylphtalate as plasticizer. Different Polymer Inclusion Membranes were characterized using physical and chemical techniques as well as Fourier transform infrared, thermogravimetric analysis, and scanning electron microscopy. Transport of lead and cadmium in aqueous solution has been studied using these systems. The selective separation of these membranes is accomplished by the presence of specific compounds, called carriers, in the membrane phase. The carriers are responsible to facilitate the transport of the target component across selective membranes. The influence of the membrane nature has been studied using some supports of different physical characteristics. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46592.     

Effect of adamantyl methacrylate on the thermal and mechanical properties of thermosensitive poly(N‐isopropylacrylamide) hydrogels

A series of thermosensitive hydrogels containing adamantyl groups were fabricated by copolymerization of N‐isopropylacrylamide and adamantyl methacrylate (AdMA). The thermal properties of such copolymeric hydrogels were studied by differential scanning calorimetry. The mechanical properties were emphasized through compression, tension, and dynamic mechanical analysis (DMA). Moreover, Rubber elasticity theory was used to evaluate the network parameters based on compressive stress–strain measurements. The results indicate that both the microstructure and physical properties strongly depend on the quantity of AdMA in the copolymeric gels. As the content of AdMA increases, the volume phase transition temperature of hydrogels decreases linearly, and the mechanical strength can be significantly improved, the effective crosslinking density (ν_e) increases monotonously, while the polymer‐water interaction parameter (χ) decreases first and then increases with AdMA content. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Temperature/pH‐sensitive comb‐type graft hydrogels composed of chitosan and poly(N‐isopropylacrylamide)

Comb‐type graft hydrogels, composed of chitosan and poly(N‐isopropylacrylamide) (PNIPAAm), were prepared to manifest rapid temperature and pH sensitivity. Instead of directly grafting the NIPAAm monomer onto the chitosan chain, semitelechelic PNIPAAm with carboxyl end group was synthesized by radical polymerization using 3‐mercaptopropionic acid as the chain‐transfer agent, and was grafted onto chitosan having amino groups. The comb‐type hydrogels were prepared with two different graft yields and grafting regions, such as surface‐ and bulk‐grafting, and then compared with a chitosan hydrogel. The synthesis of telechelic PNIPAAm and the formation of amide group were confirmed by using FTIR spectroscopy and gel permeation chromatography. Results from the water state and thermal stability revealed that the introduction of the PNIPAAm side chain disturbed the ordered arrangement of the chitosan molecule, resulting in an increase in the equilibrium water content. Comb‐type graft hydrogels showed rapid temperature and pH sensitivity because of the free‐ended PNIPAAm attached to the chitosan main chain and the chitosan amino group itself, respectively. In particular, the surface graft hydrogel maintained its dimension at low pH, although the chitosan main chain was not crosslinked, whereas chitosan and bulk graft hydrogel were dissolved as a result of the coating effect of pH‐independent PNIPAAm. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2612–2620, 2004     

Synthesis and characterization of fast responsive thermo‐ and pH‐sensitive poly[(N,N‐diethylacrylamide)‐co‐(acrylic acid)] hydrogels

BACKGROUND: A considerable amount of research has been focused on smart hydrogels that can respond to external environmental stimuli, especially temperature and pH. In this study, fast responsive thermo‐ and pH‐sensitive poly[(N,N‐diethylacrylamide)‐co‐(acrylic acid)] hydrogels were prepared by free radical copolymerization in aqueous solution using poly(ethylene glycol) (PEG) as a pore‐forming agent. RESULTS: Swelling studies showed that the hydrogels produced had both temperature and pH sensitivity. The deswelling kinetics at high temperature demonstrated that the shrinking rates were influenced by the addition of the pore‐forming agent and the amount of acrylic acid in the initial total monomers. The deswelling curves in low‐buffer solutions had two stages. Pulsatile swelling studies indicated that the PEG‐modified hydrogels were superior to the normal ones. These different swelling properties were further confirmed by the results of scanning electron microscopy. CONCLUSION: Such fast responsive thermo‐ and pH‐sensitive hydrogels are expected to be useful in biomedical fields for stimuli‐responsive drug delivery systems. Copyright © 2008 Society of Chemical Industry     

Swelling of pH‐sensitive chitosan–poly(vinyl alcohol) hydrogels

The swelling properties of different chitosan–poly(vinyl alcohol) (PVA) hydrogels were investigated as functions of the medium pH and salt concentration. The maximum swelling ability of the hydrogels was at a buffer pH of approximately 3, regardless of the PVA content in the hydrogels. The maximum mass of the swollen hydrogels was about 13 times that of their contracted counterparts. The cyclical swelling and contraction between pH 3 and pH 7 buffers and pH 3 and pH 3 buffers with salt confirmed the Donnan swelling mechanism of these hydrogels. The swelling mechanism was considered the transfer of water molecules driven by a concentration gradient. This was represented by a simplified mass‐balance model, which neglected the effect of the ionization reaction, for the initial swelling period. The effective mass‐transfer coefficient of water molecules during swelling, estimated with this model, gradually decreased with increasing PVA content in the hydrogels. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 4665–4671, 2006     

Kinetic analysis of poly(N‐isopropylacrylamide‐co‐dimethylaminoethyl methacrylate) microgel latex formation

Curves of the conversion and particle size versus the time in the preparation of poly(N‐isopropylacrylamide‐co‐dimethylaminoethyl methacrylate) microgel latices by surfactant‐free emulsion polymerization were measured. The copolymerization reactions were rapid, and their rates increased with the dimethylaminoethyl methacrylate (DMAEMA) concentration in the polymerization recipe. Particle formation occurred by a homogeneous nucleation mechanism, in which DMAEMA helped to colloidally stabilize the primary particles. In addition, a strong dependence of the water‐soluble‐polymer (WSP) formation on the DMAEMA concentration was found, and the DMAEMA content in the WSP was significantly higher than that in the microgel particle. A drastic variation of the crosslinking density within the microgel particle during the polymerization process was found through a comparison of the particle size determined by quasi‐elastic light scattering with that determined by transmission electron microscopy. Finally, on the basis of these results, the mechanism of particle formation in this polymerization process was examined. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 839–846, 2004     

Terpolymerization kinetics of N,N‐dimethylaminoethyl methacrylate/alkyl methacrylate/styrene systems

Low conversion kinetics of terpolymerization of N,N‐dimethylaminoethyl methacrylate (DMAEM) and dodecyl methacrylate (DDMA) with methyl methacrylate (MMA) or styrene (ST) was investigated. Reactions were performed at 70°C, in toluene solutions, using peroxide initiator. The interdependence between terpolymer and monomer feed composition was successfully described by Alfrey‐Goldfinger equation and the unitary, binary, and ternary azeotropes were calculated. In MMA‐containing system, the wide pseudoazeotropic region with existence of true azeotropic point was observed and experimentally confirmed at the DMAEM:MMA:DDMA molar ratio of 56:41:3. In the ST‐containing system compositional heterogeneity was significant, more than 10 mol%. Required copolymerization reactivity ratios were determined by linear and nonlinear methods. The glass transition temperatures of synthesized terpolymers are found to be between those of the corresponding homopolymers and relative to their content. Increase in the MMA or ST contents and decrease in the DDMA content in terpolymers results in an increase in their glass transition temperatures. POLYM. ENG. SCI., 2010. © 2009 Society of Plastics Engineers     

Cationic hybrids from poly(N,N‐dimethylaminoethyl methacrylate) covalently crosslinked with chloroalkyl silicone derivatives effective in binding anionic dyes

The synthesis and characterization of some novel ionic organic/inorganic hybrids containing quaternary ammonium salt groups in the side chain, built on the basis of poly(N,N‐dimethylaminoethyl methacrylate), as an organic component and cation provider, and chloroalkyl‐functionalized silicone derivatives as crosslinkers and anion generators, are reported in this work. The resulted structures were investigated using Fourier transform infrared spectroscopy, differential scanning calorimetry, thermogravimetric analysis, and energy dispersive X‐ray spectroscopy. The swelling behavior of the ionic hybrids in water as a function of pH as well as the water vapor sorption capacity in dynamic regime was also studied. The cationic hybrids have a higher swelling capacity at pH 2 compared with deionized water (pH 6) due to the presence of tertiary amine groups belonging to the organic compound. The ionic organic/inorganic hybrids were tested as potential sorbents for anionic species such as dyes [e.g., methyl orange (MO)]. The equilibrium sorption capacity increased with the increase of the organic component up to around 32 mg MO/g hybrid. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 43942.     

Kinetics of solvent responsiveness in poly(N,N‐dimethylacrylamide) hydrogels of different morphology

Crosslinked poly(N,N‐dimethylacrylamide) hydrogel samples were synthesized with various total comonomer concentrations and crosslinker ratios in the reacting mixture, and at two different temperatures: room temperature and the boiling point of the reacting mixture, about 80 °C. During gelation of samples prepared at the higher temperature, the bubbles of the boiling system were trapped in positions homogeneously distributed, and post‐gel reactions fixed them. These samples were macroporous, showing about three times the swelling capacity of conventional hydrogels synthesized at room temperature with the same composition. Both types of hydrogel swollen at equilibrium in water deswelled exponentially with time when they were immersed in acetone or dioxane. The rate of shrinking was higher for macroporous than for conventional samples and it was smaller in dioxane, the solvent with higher viscosity (η), although there was no proportionality to the solvent fluidity, η^?1. The morphology, which was in the scale of micrometres (as revealed by scanning electron microscopy), played a minor role in the shrinking rates of both types of gels. The excess swelling and the faster solvent response of macroporous gels were ascribed to the store and draining capacity of macropores at the millimetre scale. Copyright © 2005 Society of Chemical Industry     

Synthesis,characterization and thermal degradation of dual temperature‐ and pH‐sensitive RAFT‐made copolymers of N,N‐(dimethylamino)ethyl methacrylate and methyl methacrylate

Poly{[(N,N‐(dimethylamino)ethyl methacrylate]‐co‐(methyl methacrylate)} copolymers of various compositions were synthesized by reversible addition‐fragmentation chain transfer (RAFT) polymerization at 70 °C in N,N‐dimethylformamide. The polymer molecular weights and molecular weight distributions were obtained from size exclusion chromatography, and they indicated the controlled nature of the RAFT polymerizations; the polydispersity indices are in the range 1.1–1.3. The reactivity ratios of N,N‐(dimethylamino)ethyl methacrylate (DMAEMA) and methyl methacrylate (MMA) (r_DMAEMA = 0.925 and r_MMA = 0.854) were computed by the extended Kelen–Tüdös method at high conversions, using compositions obtained from ¹H NMR. The pH‐ and temperature‐sensitive behaviour were studied in aqueous solution to confirm dual responsiveness of these copolymers. The thermal properties of the copolymers with various compositions were investigated by differential scanning calorimetry and thermogravimetric analysis. The kinetics of thermal degradation were determined by Friedmann and Chang techniques to evaluate various parameters such as the activation energy, the order and the frequency factor. © 2012 Society of Chemical Industry     

Swelling characteristics of thermo‐ sensitive poly[(2‐diethylaminoethyl methacrylate)‐co‐(N,N‐dimethylacrylamide)] porous hydrogels

Temperature‐sensitive poly[(2‐diethylaminoethyl methacrylate)‐co‐(N,N‐dimethylacrylamide)] [P(DEAEMA‐co‐DMAAm)] hydrogels with five different DMAAm contents were synthesized with and without the addition of sodium carbonate as porosity generator. The synthesized hydrogels were characterized with dry gel density measurements, scanning electron microscopy observation and the determination of swelling ratio. The influence of the pore‐forming agent and content of DMAAm on swelling ratio and network parameters such as polymer–solvent interaction parameter (χ), average molecular mass between crosslinks (M?_c) and mesh size (ζ) of the cryogels are reported and discussed. The swelling and deswelling rates of the porous hydrogels are much faster than for the same type of hydrogels prepared via conventional methods. At a temperature below the volume phase transition temperature, the macroporous hydrogels also absorbed larger amounts water compared to that of conventional hydrogels and showed obviously higher equilibrated swelling ratios in aqueous medium. In particular, the unique macroporous structure provided numerous water channels for water diffusion in or out of the matrix and, therefore, an improved response rate to the external temperature changes during the deswelling and swelling processes. These properties are attributed to the macroporous and regularly arranged network of the porous hydrogels. Scanning electron micrographs reveal that the macroporous network structure of the hydrogels can be adjusted by applying porosity generation methods during the polymerization reaction. Copyright © 2007 Society of Chemical Industry     

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     

DNA adsorption on poly(N,N‐dimethylacrylamide)‐grafted chitosan hydrogels

In this study, poly(N,N‐dimethylacrylamide) grafted chitosan (PDMAAm‐g‐CT) hydrogels were prepared for deoxyribonucleic acid (DNA) adsorption. Instead of directly grafting the N,N‐dimethylacrylamide (DMAAm) monomer onto the chitosan (CT) chains, poly(N,N‐dimethylacrylamide) with carboxylic acid end group (PDMAAm‐COOH) was firstly synthesized by free‐radical polymerization using mercaptoacetic acid (MAAc) as the chain‐transfer agent and then grafted onto the CT having amino groups. The synthesis of PDMAAm‐COOH and its grafting onto the CT chains were confirmed by attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy. From gel permeation chromatography measurements, the number‐average molecular weight (M _n) and polydispersity index of PDMAAm‐COOH were found as 2400 g/mol and 2.3, respectively. The PDMAAm‐g‐CT hydrogels were utilized as the adsorbents in DNA adsorption experiments conducted at +4°C in a trisEDTA solution of pH 7.4. The hydrogels produced with higher PDMAAm‐COOH content exhibited higher DNA adsorption capacity. The DNA adsorption capacity up to 4620 μg DNA/g dry gel could be achieved with the PDMAAm‐g‐CT hydrogels prepared in 80.0 wt % PDMAAm‐COOH feed concentration. This value is approximately seven times higher than that of CT alone. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Preparation and properties of temperature‐sensitive soy protein/poly(N‐isopropylacrylamide) interpenetrating polymer network hydrogels

Temperature‐sensitive interpenetrating polymer network (IPN) hydrogels based on soy protein and poly(N‐isopropylacrylamide) were successfully prepared. The structure and properties were systematically characterized using Fourier transform infrared spectroscopy, scanning electron microscopy, differential scanning calorimetry and thermogravimetric analysis, and the swelling and deswelling behavior was also investigated. It was found that the hydrogels had good miscibility, thermal stability and temperature sensitivity, and the lower critical solution temperature was ca 32 °C. Changing the content of soy protein or crosslinker could be used to control the swelling behavior, water retention and network structure of the IPN hydrogels. The results show that the novel IPN hydrogels may be of potential interest in drug delivery systems. Copyright © 2011 Society of Chemical Industry