Electrolyte‐ and pH‐responsive polyampholytes with potential as viscosity‐control agents in enhanced petroleum recovery

Low‐charge‐density amphoteric copolymers and terpolymers composed of AM, the cationic comonomer (3‐acrylamidopropyl)trimethyl ammonium chloride, and amino acid derived monomers (e.g., N‐acryloyl valine, N‐acryloyl alanine, and N‐acryloyl aspartate) have been prepared via free‐radical polymerization in aqueous media. These terpolymers with random charge distributions have been compared to terpolymers of like compositions containing the anionic comonomer sodium 3‐acrylamido‐3‐methylbutanoate. Terpolymer compositions determined by ¹³C‐ and ¹H‐NMR spectroscopy, terpolymer molecular weights and polydispersity indices obtained via size exclusion chromatography/multi‐angle laser light scattering, and hydrodynamic dimensions determined via dynamic light scattering have allowed a direct comparison of the fundamental parameters affecting the behavioral characteristics. The solution properties of low‐charge‐density amphoteric copolymers and terpolymers have been studied as functions of the solution pH, ionic strength, and polymer concentration. The low‐charge‐density terpolymers display excellent solubility in deionized water with no phase separation. The charge‐balanced terpolymers exhibit antipolyelectrolyte behavior at pH values greater than or equal to 6.5 ± 0.2. As the solution pH decreases, these charge‐balanced terpolymers become increasingly cationic because of the protonation of the anionic repeat units. The aqueous solution behavior (i.e., globule‐ to‐coil transition at the isoelectric point in the presence of salt and globule elongation with increasing charge asymmetry) of the terpolymers in the dilute regime correlates well with that predicted by the polyampholyte solution theories. An examination of the comonomer charge density, hydrogen‐bonding ability, and spacer group (e.g., the moiety separating the ionic group from the polymer chain) indicates that conformational restrictions of the sodium 3‐acrylamido‐3‐methylbutanoate and N‐acryloyl valine segments result in increased chain stiffness and higher solution viscosities in deionized water and brine solutions. On the other hand, the terpolymers with N‐acryloyl alanine and N‐acryloyl aspartate segments are more responsive to changes in the salt concentration. An assessment of the effects of the terpolymer structure on the viscosity under specified conditions of the ionic strength and pH from these studies should allow for rational design of optimized systems for enhanced petroleum recovery. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007.     

Preparation and pH‐sensitive swelling behavior of physically crosslinked polyampholyte gels

A novel polyampholyte hydrogels were prepared by free radical aqueous copolymerization of ionic complex consisting of acrylic acid (AAc), (N,N‐diethylamino) ethyl methacrylate (DEAEM), and acrylamide (designated as PADA). Without any chemical crosslinker, the formation of PADA network structures was mainly attributed to the electrostatic interaction of AAc (anionic monomer) and DEAEM (cationic monomer). The PADA gels exhibited a typical swelling behavior of polyampholyte gels in buffer solutions. The hysteresis of isoelectric point (pI) for PADA gels was observed after preswollen in alkaline solutions. The swelling behavior of PADA gels in response to change of pH was investigated. It was found that the equilibrium swelling ratio orderly decreased in buffer solutions with alternating pH between 2.2 and 5. An abrupt swelling was observed for the hydrogels at the pH near isoelectric point in the earlier stage of swelling process. The study of swelling kinetics of the hydrogels showed that the swelling process was in agreement with the second‐order swelling kinetics. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 3857–3861, 2006     

Water‐soluble dual responsive polythiophene‐g‐poly(methoxyethoxy ethyl methacrylate)‐co‐poly(N,N‐diethylamino ethyl methacrylate) for different applications

Polythiophene (PT) based dual responsive water‐soluble graft copolymer (PT‐g‐[poly(methoxyethoxy ethyl methacrylate)‐co‐poly(N,N‐diethylamino ethyl methacrylate)]) (PT‐g‐P(MeO₂MA‐co‐DEAEMA)) (PTDE) has been synthesized by random copolymerization of methoxyethoxy ethyl methacrylate (MeO₂MA) and N,N‐diethylamino ethyl methacrylate (DEAEMA) at 30 °C on the 2,5‐poly(3‐[1‐ethyl‐2‐(2‐ bromoisobutyrate)] thiophene) (PTI) macroinitiator using the Cu based atom transfer radical polymerization technique. The PTDE graft copolymer was characterized by gel permeation chromatography and ¹H NMR techniques and it exhibits thermo‐reversible solubility in water showing a lower critical solution temperature of ca 42 °C in neutral aqueous solution. The PTDE graft copolymer contains a fluorescent PT backbone, and interestingly the system exhibits doubling of fluorescence intensity with rising temperature over the temperature range 41–45 °C at pH 7. The PTDE system therefore acts following the principle of the polymeric AND logic gate and it is also found to be effective in sensing of nitroaromatics, particularly picric acid. The influence of chain hydrophobicity on the logic operation and on the sensing of nitroaromatics is discussed. © 2014 Society of Chemical Industry     

Swelling behavior of pH‐ and temperature‐sensitive copolymers containing 2‐hydroxy‐ethyl methacrylate and N‐vinyl‐2‐pyrrolidone crosslinked with new crosslinkers

Copolymers of 2‐hydroxyethyl methacrylate (HEMA) and N‐vinyl‐2‐pyrrolidone (VP) and homopolymers of HEMA and VP were crosslinked in the presence of different mol% of melamine trimethacrylamide (MMAm) and melamine triacrylamide (MAAm) as crosslinkers by bulk radical polymerization. The resultant xerogels were characterized by extracting the soluble fractions and measuring the equilibrium water content. Lower critical solution transition temperatures (LCST) were measured by DSC. The properties of crosslinked HEMA and VP copolymers, VP and HEMA series were evaluated in terms of compositional drift of polymerization, heterogeneous crosslinking, and chemical structure of the relevant components. Soluble fractions of the crosslinked networks were reduced by varying the MAAm and MMAm concentrations. The influence of environmental conditions such as temperature and pH on the swelling behavior of these polymeric gels was investigated. The swelling behaviors of the resulting gels show pH sensitivity. This behavior is explained on the basis that amide groups of VP or crosslinkers could be hydrolyzed to form negatively charged carboxylate ion groups in the produced networks in response to an external pH variation. Copyright © 2004 Society of Chemical Industry     

Effect of pH,ionic strength,and temperature on uranyl ion adsorption by poly(N‐vinyl 2‐pyrrolidone‐g‐tartaric acid) hydrogels

Poly‐electrolyte N‐vinyl 2‐pyrrolidone‐g‐tartaric acid (PVP‐g‐TA) hydrogels with varying compositions were prepared in the form of rods from ternary mixtures of N‐vinyl 2‐pyrrolidone/tartaric acid/water. The effect of external stimuli, such as the solution pH, ionic strength, and temperature, on uranyl adsorption by these hydrogels was investigated. Uranyl adsorption capacities of the hydrogels were determined to be 53.2–72.2 (mg UO/g dry gel) at pH 1.8, and 35.3–60.7 (mg UO/g dry gel) at pH 3.8, depending on the amount of TA in the hydrogel. The adsorption studies have shown that the temperature and the ionic strength of the swelling solution also influence uranyl ion adsorption by PVP‐g‐TA hydrogels. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 78: 2219–2226, 2000     

Fast responsive poly(acrylic acid‐co‐N‐isopropyl acrylamide) hydrogels based on new crosslinker

Novel dual temperature‐ and pH‐sensitive poly(acrylic acid‐co‐N‐isopropylacrylamide), AA/NIPAAm, hydrogels were successfully prepared by chemical crosslinking with crosslinkers. Copolymers of AA/NIPAAm were crosslinked in the presence of different mol % of N,N‐methylene bisacrylamide (MBA) and melamine triacrylamide (MAAm) as crosslinkers by bulk radical polymerization. The resultant xerogels were characterized by extracting the soluble fractions and measuring the equilibrium water content. Lower critical solution transition temperatures (LCST) were measured by DSC. The properties of crosslinked AA/NIPAAm series are evaluated in terms of compositional drift of polymerization, heterogeneous crosslinking, and chemical structure of the relevant components. Soluble fractions of the crosslinked networks were reduced by varying the MAAm and MBA concentrations. The influence of environmental conditions such as temperature and pH on the swelling behavior of these polymeric gels was investigated. The swelling behaviors of the resulting gels show pH sensitivity. The prepared MAAm type AA/NIPAAm hydrogels exhibited a more rapid deswelling rate than MBA type AA/NIPAAm hydrogels in ultra pure water in response to abrupt changes from 20°C to 50°C. The results of this study provide valuable information regarding the development of dual stimuli‐sensitive hydrogels with fast responsiveness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Temperature,pH, and reduction triple‐stimuli‐responsive inner‐layer crosslinked micelles as nanocarriers for controlled release

Temperature, pH, and reduction triple‐stimuli‐responsive inner‐layer crosslinked micelles as nanocarriers for drug delivery and release are designed. The well‐defined tetrablock copolymer poly(polyethylene glycol methacrylate)–poly[2‐(dimethylamino) ethyl methacrylate]–poly(N‐isopropylacrylamide)–poly(methylacrylic acid) (PPEGMA‐PDMAEMA‐PNIPAM‐PMAA) is synthesized via atom transfer radical polymerization, click chemistry, and esterolysis reaction. The tetrablock copolymer self‐assembles into noncrosslinked micelles in acidic aqueous solution. The core‐crosslinked micelles, shell‐crosslinked micelles, and shell–core dilayer‐crosslinked micelles are prepared via quaternization reaction or carbodiimide chemistry reaction. The crosslinked micelles are used as drug carriers to load doxorubicin (DOX), and the drug encapsulation efficiency with 20% feed ratio reached 59.2%, 73.1%, and 86.1%, respectively. The cumulative release rate of DOX is accelerated by single or combined stimulations. The MTT (3‐(4,5‐Dimethylthiazol‐2‐yl)‐2,5‐diphenyltetrazolium bromide) assay verifies that the inner‐layer crosslinked micelles show excellent cytocompatibility, and DOX‐loaded micelles exhibit significantly higher inhibition for HepG2 cell proliferation. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46714.     

Bioengineering functional copolymers: V. Synthesis,LCST, and thermal behavior of poly(N‐isopropyl acrylamide‐co‐p‐vinylphenylboronic acid)

New boron‐containing stimuli‐responsive (pH‐ and temperature‐sensitive) copolymers were synthesized and characterized. Structure and composition of copolymers were determined by FTIR and ¹H‐NMR spectroscopy, and elemental analysis and titration (N and B contents for NIPA and VPBA unit, respectively). By DSC and XRD measurements, it is established that the synthesized copolymers have a semicrystalline structure due to formation of intra‐ and/or intermolecular H‐bonded supramolecular architecture. The copolymer composition–structure–property relationship indicates semicrystalline structure of copolymers with different compositions, degrees of crystallinity, and thermal and stimuli‐responsive behaviors depends on the content of boron‐containing monomer linkage. Results of DSC, DTA, and TGA analyses indicated that copolymers have T_g and T_m and high thermal stability. These water‐soluble and temperature‐ and pH‐sensitive amphiphilic copolymers can be used as polymeric carries for delivery of biological entities for diverse biomedical use, including boron neutron capture therapy. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 95: 573–582, 2005     

Properties of a poly(acrylamide‐co‐diallyl dimethyl ammonium chloride) hydrogel synthesized in a water–ionic liquid binary system

A novel copolymer hydrogel, poly(acrylamide‐co‐diallyl dimethyl ammonium chloride), was prepared by the radical copolymerization of acrylamide and diallyl dimethyl ammonium chloride in an ionic liquid (IL)–water binary system in the presence of the crosslinker N,N′‐methylene bisacrylamide. The equilibrium swelling ratios of the hydrogels synthesized in the IL–water binary system increased with the content of IL and were remarkably higher than that of the gel synthesized in water. Differential scanning calorimetry measurements showed that the glass‐transition temperatures of the dry hydrogels that were synthesized in the IL–water binary system were remarkably lower than that of the gel synthesized in pure water. The mechanical properties of the gels synthesized in both water and the IL–water binary system were characterized with a universal material‐testing machine. The results show that fracture toughness of the hydrogels was improved when they were synthesized in the IL–water binary system. The gel shrank under a direct‐current electric field. The response rates of the gels that were synthesized with the IL–water binary system were faster than that of the gel synthesized in water. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2010     

A convenient synthesis of macroporous polymer‐supported supernucleophilic reagent and linear macromolecules

N,N′‐Bis(4‐pyridinyl)piperazine and N‐(4‐pyridinyl)piperazine have been prepared by treatment of piperazine with 4‐chloropyridine. N,N′‐Bis(4‐pyridinyl)piperazine (bis‐DMAP) is similar to a couple of 4‐(N,N‐dimethylamino)pyridine (DMAP). N‐(4‐Pyridinyl)piperazine as reactive group can be linked onto the macroporous polymeric carrier producing a polymer‐bound catalyst. A linear epoxy polymer containing the supernucleophilic functional groups have been synthesized by reaction of epichlorohydrin and 4‐aminopyridine. The linear polymeric catalysts have been braced by the macroporous resin to obtain a polymer‐supported linear polymeric catalyst. It is found that catalytic activity of bis‐DMAP approaches that of DMAP. The activity of the polymer‐supported linear polymeric catalyst is higher than that of the polymer‐bound catalyst in the acetylation of tert‐butyl alcohol, as monitored by gas–liquid chromatography. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 75: 593–597, 2000     

pH‐sensitive acrylic‐based copolymeric hydrogels for the controlled release of a pesticide and a micronutrient

Acrylic‐based copolymers of methyl methacrylate (MMA) and methacrylic acid (MAA) have been prepared by solution and bulk polymerization techniques using benzoyl peroxide (BPO) as an initiator. Three polymers were prepared with a varying ratio of MMA/MAA. In an effort to increase the hydrophilicity of the matrix, one MMA/MAA polymer was prepared by adding an additional amount of 2‐hydroxy ethyl methacrylate (HEMA). All the polymers were crosslinked in situ by ethylene glycol dimethacrylate (EGDMA). These polymers were characterized by Fourier transform infrared spectroscopy and differential scanning calorimetry. Viscous flow characteristics were determined from solution viscosity and rheological measurements. Dynamic and equilibrium swelling experiments were carried out under varying pH conditions (i.e., 0.1N NaOH, 0.1N HCl, and double‐distilled water). Partially crosslinked hydrogels show varying hydrophilicity because of the presence of carboxylic acid groups making them pH‐responsive. Swelling increased with an increasing number of —COOH groups on the polymer backbone and the hydrophilicity varied with changing pH. Cypermethrin, a widely used pesticide, and cupric sulfate, a model micronutrient, were loaded into these pH‐sensitive hydrogels to investigate their controlled release characteristics. The in vitro release rates of both compounds have been carried out under static dissolution conditions at 30°C. Release data have been fitted to an empirical relation to estimate transport parameters. The release results have been discussed in terms of the varying hydrophilicity of the hydrogel network polymers. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 394–403, 2003     

Interaction of a new anesthetic drug richlocain with linear and weakly crosslinked poly‐N‐vinylpyrrolidone

The properties of complexes of richlocain, a new local anesthetic drug, with linear and weakly crosslinked poly‐N‐vinylpyrrolidone were investigated with changes in media properties of pH, temperature, and solvent thermodynamic quality. The kinetics and activation energy of drug release from the gel matrix were determined. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 89: 2977–2981, 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     

Effect of the nature of the crosslinking agent on the metal‐ion complexation characteristics of 4 mol % DVB‐ and NNMBA‐crosslinked polyacrylamide‐supported glycines

Metal‐ion complexation behavior of glycine functions supported on divinylbenzene (DVB)‐ and N,N′‐methylene bisacrylamide (NNMBA)‐crosslinked polyacrylamide was carried out toward Co(II), Ni(II), Cu(II), and Zn(II) ions. The polymeric ligands and the derived metal complexes were characterized by IR, UV, and EPR spectra and by SEM. The metal‐ion complexation of the rigid DVB‐crosslinked system is lower than that of the semirigid NNMBA‐crosslinked system. The glycine ligands renervated after the desorption of the metal ions showed an unusual specificity toward the desorbed metal ion. The low degree of crosslinking makes the desorption process simple and shows fast rebinding kinetics. The metal‐ion‐desorbed polymeric ligands would have pockets or holes characteristic of the desorbed metal ion, resulting in its specific rebinding. The rigidity of the crosslinking also determines the kinetics of metal‐ion rebinding. The specificity and selectivity characteristics of the crosslinked polymeric ligand was found to be increased as the crosslinking agent changes from semirigid NNMBA to rigid and hydrophobic DVB. Thus, copper‐desorbed resins showed an increased specificity toward copper ions and selectively binds copper ions from a mixture of copper and cobalt ions. The metal‐ion specificity and selectivity characteristics of the metal‐ion‐desorbed system is exploited for the concentration of desorbed metal ions from a mixture of metal ions. The resin is amenable for a continuous process and can be regenerated several times. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3432–3444, 1999     

Biocidal polystyrene beads. III. Comparison of N‐halamine and quat functional groups

A comparison has been made between the biocidal efficacies of N‐chlorinated polymeric beads and two derivatives of polyquat beads. Biocidal effects were measured after brief contact exposures of aqueous suspensions of either Staphylococcus aureus or Escherichia coli to the water‐insoluble beads. The polymeric backbone was held the same in all three types of beads, so they differed only in their biocidal derivative moieties. In all cases, functionalization of crosslinked chloromethylated polystyrene beads was performed to introduce the biocidal properties. Synthetic methods and test data will be presented. The most effective biocide, as measured by degree of inactivation in the shortest contact time of the two species of bacteria, was the N‐chlorinated hydantoinyl derivative of methylated polystyrene. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 363–367, 2004     

pH‐sensitive uniform gel beads for DNA adsorption

Uniform gel beads 3 mm in diameter were obtained by the suspension polymerization of an amine functionalized monomer, N‐3‐(dimethyl amino)propylmethacrylamide (DMAPM). The polymerization of DMAPM in the form of uniform droplets could be achieved at room temperature in an aqueous dispersion medium by using Ca–alginate gel as the polymerization mold. In this preparation, potassium persulfate/tetramethyl ethylenediamine and sodium alginate/calcium chloride were used as the redox initiator and the stabilizer systems, respectively. The crosslinked DMAPM gel beads exhibited pH‐sensitive, reversible swelling–deswelling behavior. The uniform gel beads were also obtained by the copolymerization of DMAPM and acrylamide (AA) in the same polymerization system. Although copolymer gel beads with higher pH sensitivities were obtained with increasing feed concentration of DMAPM, the total monomer conversion decreased. Crosslinked DMAPM and DMAPM–AA copolymer gel beads were utilized as sorbents for DNA adsorption. The gel beads produced with higher DMAPM feed concentration exhibited higher equilibrium DNA adsorption capacity. The DNA equilibrium adsorption capacities up to 50 mg DNA/g dry gel could be achieved with the crosslinked DMAPM gel beads. This value was reasonably higher relative to the previously reported adsorption capacities of known sorbents. © 2000 John Wiley & Sons, Inc. J Appl Polym Sci 77: 3154–3161, 2000     

Preparation of composite‐crosslinked poly(N‐isopropylacrylamide) gel layer and characteristics of reverse hydrophilic–hydrophobic surface

The composite‐crosslinked poly(N‐isopropylacrylamide) (PNIPAAm) gels were prepared by grafting N‐isopropylacrylamide on the surface of glass plates modified by organosilanes. The glass plates as the substrate increase the mechanical strength of composite PNIPAAm gel layers. We investigated the effects of a series of organosilanes and the reaction time of organosilanes on surface characteristics, such as the static contact angle and the layer thickness. We discuss the equilibrium swelling ratio and the water release behavior of the gel layers in terms of the crosslinking density of the composite gels. The composite gels exhibit not only the characteristics of remarkable water release but also the reversed hydrophilic–hydrophobic surface properties. The gel layers are hydrophilic under 25°C and change to hydrophobic above 40°C. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1–11, 1999     

Electrolyte and pH responsive surfactant association in ionic semi‐interpenetrating networks containing cellulose or chitin synthesized in lithium chloride–N,N‐dimethylacetamide

Semi‐interpenetrating networks (SIPNs) of N,N‐dimethylacrylamide (DMAm)–N,N‐dimethylamino‐ethylacrylamide (DMAEAm), or N,N‐dimethylacrylamide (DMAm)–2‐acrylamido‐2‐methyl‐1‐propanesulfonic acid (AMPS) containing cellulose or chitin were synthesized in 9% LiCl–N,N‐dimethylacetamide (DMAc). The SIPNs were formulated to contain (1, 2, or 5% w/w) cellulose or 0.8% w/w chitin. Control systems (without polysaccharide) were also synthesized in 9% LiCl–DMAc. An acrylamide (Am)–AMPS hydrogel was synthesized for comparison with the SIPN composites. The swelling behavior of these materials was investigated as a function of pH (DMAEAm‐containing networks) or electrolyte concentration (AMPS‐containing networks). The DMAm–AMPS materials were found to have higher equilibrium water content (EWC) values in deionized water than the DMAm–DMAEAm materials. The EWC of the DMAm–DMAEAm materials was largest between pH 4 and 5 due to the protonation of the tertiary amine, with the chitin‐containing material exhibiting the largest EWC. The DMAm–AMPS materials exhibited a decrease in EWC values with an increase in electrolyte concentration. Polymer–surfactant interactions were shown to exist for surfactants of opposite charge of the ionic mer units incorporated into the polymeric network. Surfactant sequestration by the polysaccharide‐containing materials was greater than that of the control gels; however, the rates of surfactant binding were lower. Release of the bound surfactant was achieved by the disruption of the charge–charge interactions by changing the pH of the medium (DMAEAm‐containing networks) or by the addition of electrolyte (AMPS‐containing networks). The DMAm–DMAEAm SIPNs released only 4% of the surfactant originally sequestered. By contrast, the DMAm–AMPS SIPNs released approximately 80%. The control Am–AMPS hydrogel–surfactant complex collapsed in the presence of electrolyte, and no surfactant was released from the complex. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 989–998, 1999     

pH‐thermoreversible hydrogels. I. Synthesis and swelling behaviors of the (N‐isopropylacrylamide‐co‐acrylamide‐co‐2‐hydroxyethyl methacrylate) copolymeric hydrogels

A series of pH‐thermoreversible hydrogels that exhibited volume phase transition was synthesized by various molar ratios of N‐isopropylacrylamide (NIPAAm), acrylamide (AAm), and 2‐hydroxyethyl methacrylate (HEMA). The influence of environmental conditions such as temperature and pH value on the swelling behavior of these copolymeric gels was investigated. Results showed that the hydrogels exhibited different equilibrium swelling ratios in different pH solutions. Amide groups could be hydrolyzed to form negatively charged carboxylate ion groups in their hydrophilic polymeric network in response to an external pH variation. The pH sensitivities of these gels also depended on the AAm content in the copolymeric gels; thus the greater the AAm content, the higher the pH sensitivity. These hydrogels, based on a temperature‐sensitive hydrogel, demonstrated a significant change of equilibrium swelling in aqueous media between a highly solvated, swollen gel state and a dehydrated network response to small variations of temperature. pH‐thermoreversible hydrogels were used for a study of the release of a model drug, caffeine, with changes in temperature. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 221–231, 1999     

6‐O‐dodecyl‐chitosan carbamate–based pH‐responsive polymeric micelles for gene delivery

pH‐responsiveness is highly desirable in the stimuli‐responsive controlled release because of the distinct advantages of the fast response of pH‐triggered release and the available pH‐difference between intra‐ and extra‐cells. The present work reported a kind of novel pH‐responsive polymeric micelles, which was derived from biopolymer of 6‐O‐dodecyl‐chitosan carbamate (DCC) and evaluated as gene‐controlled release vector. The amphiphilic and amino‐rich DDC was synthesized through a protection‐graft‐deprotection method. ¹³C CP/MAS NMR, FTIR, and elemental analysis identified that dodecyls were chemoselectively grafting at 6‐hydroxyls of chitosan via the pH‐responsive bonds of carbamate, and the substitute degree (SD) was 14%. Transmission electron microscopy (TEM) and dynamic light scattering (DLS) showed that DCC self‐assembled into polymeric micelles in aqueous solutions. The DCC polymeric micelles formed complexes with pDNA, which was elucidated by Gel retardation, TEM, and DLS. Transfection and cytotoxicity assays in A549 cells showed that DCC polymeric micelles were suitable for gene delivery. The improved transfection was attributed to the pH‐responsiveness and the moderate pDNA‐binding affinity, which led to easier release of pDNA intra‐cells. The synthesized DCC polymeric micelles might be a promising and safe candidate as nonviral vectors for gene delivery. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 42469.