Synthesis of millimeter‐sized hydrogel beads by inverse Pickering polymerization using starch‐based nanoparticles as emulsifier

The preparation of millimeter‐sized poly(acrylamide‐co‐acrylic acid) hydrogel beads via inverse Pickering emulsion polymerization using starch‐based nanoparticles (SNPs) as stabilizers is reported. Amphiphilic starch is fabricated by the introduction of butyl glycidyl ether groups and palmitate groups, and the hydrophobically modified SNPs are fabricated by a nanoprecipitation process. The obtained SNPs could adsorb at oil‐water interfaces to stabilize an inverse Pickering emulsion, and the effects of oil/water volume fraction ratio and SNP concentration on emulsions are comprehensively studied. Poly(acrylamide‐co‐acrylic acid) hydrogel beads with a size of approximately 1 mm are obtained by inverse Pickering emulsion polymerization stabilized by SNPs. The morphology and structure of hydrogel beads are extensively investigated, which confirms that SNPs locate on the surface of hydrogel beads and act as emulsifiers and network structures present inside the beads. Polymerization is also detected to investigate the potential formation mechanism of hydrogel beads. The pH‐responsive property of hydrogel beads and its potential application for drug delivery are also explored.     

Multistimuli responsive ternary polyampholytes: Formation and crosslinking of coacervates

A series of multiresponsive ternary polyampholytes were prepared by free‐radical copolymerization of N‐(3‐aminopropyl) methacrylamide hydrochloride (APM), methacrylic acid (MAA), and N‐(2‐hydroxyethyl) acrylamide (HEA). APM and MAA were held at 1:1 molar ratio, while the HEA monomer feed was varied between 14 and 33 mol %. Compositional drift during polymerization was monitored by ¹H nuclear magnetic resonance, and minimized by adjusting the reactivity of MAA through its degree of ionization. The resulting polyampholytes phase‐separate from aqueous solution to form coacervate droplets, depending on HEA content, pH, ionic strength, and temperature. These coacervate droplets could be covalently crosslinked and the resulting hydrogel particles were found to swell with increasing ionic strength. Such soluble and microgel polyampholytes open opportunities for new multistimuli responsive biomaterials. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 2109–2118     

Removal of methylene blue dye from aqueous solution by semi‐interpenetrating polymer network hybrid hydrogel: Optimization through Taguchi method

In this study, sodium humate/poly(acrylamide‐co‐methacrylic acid)/kaolin semi‐interpenetrating polymer network hybrid hydrogel was synthesized as an effective adsorbent for the removal of methylene blue. The morphological and structural properties, and swelling behavior in distilled water and various environments of hybrid hydrogel were investigated with different analyses and tests. The equilibrium swelling percent of hybrid hydrogel reached to 37,000% in 240 min. The parameters (agitation time, concentration, dose, temperature, and pH) affecting adsorption process for methylene blue were optimized using Taguchi method. The data obtained in optimum conditions were well fitted to Langmuir adsorption isotherm and maximum adsorption capacity was determined as 833. 33 mg/g. In the light of the results, the utilization of hybrid hydrogel with high swelling capacity is foreseen as a favored adsorbent in several separation processes. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 1070–1078     

Novel transmittance change of polyelectrolyte hydrogel in DC electric field

A novel transmittance change of poly(acrylamide‐co‐acrylic acid) hydrogel in a DC electric field was observed. Transmittance of a specimen increased when the electric field was on and decreased by removing the electric force. In certain cases, the sample was able to switch from white opaque to colorless transparent. The rate and extent of the transition depended on the applied electric potential, ambient temperature, and composition of the specimen. These observations are closely related to the dissociation of hydrogen bonding in the network induced by an external electric field. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 2290–2295, 2003     

Frontal Polymerization of Deep Eutectic Solvents Composed of Acrylic and Methacrylic Acids

Frontal polymerization of deep eutectic solvents (DESs) made with acrylic or methacrylic acid as the monomer and hydrogen bond donor was studied. Fronts with acrylic acid and choline chloride propagated more uniformly than with pure acrylic acid, so an exploration into how the DES affected frontal polymerization was performed. The hydrogen bond acceptor of the DES was replaced by several analogs to determine the effect on the DES front behavior. The analogs used were talc, DMSO, lauric acid, and stearic acid, which acted as a heat sink, inert diluent, hydrogen bonding diluent, and inert phase change material, respectively. None of the methacrylic acid‐analog systems were able to sustain a front. While the acrylic acid‐analog systems did sustain a front (with the exception of stearic acid), none of the fronts replicated the acrylic acid DES behavior. The acrylic acid–talc sample behaved more violently—like pure acrylic acid polymerization—than the acrylic acid DES, and the DMSO and lauric acid samples produced slower fronts than that of the acrylic acid DES. We propose that the reactivity of the acrylic acid and methacrylic acid is enhanced in the DES. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2017 , 55, 4046–4050     

Synthesis and characterization of a starch‐modified hydrogel as potential carrier for drug delivery system

Synthesis and characterization of a new hydrogel were carried out using a chemically modified starch (starch‐M) consisting of coupling C?C bounds coming from glycidil methacrylate (GMA) onto the polysaccharide structure. ¹³C NMR, ¹H NMR, and FT‐IR spectroscopies were used to confirm the incorporation of such groups onto the starch‐M. The hydrogel was prepared by a crosslinking polymerization of starch‐M using sodium persulfate as an initiating agent. The starch‐M hydrogel shows morphology clearly different from that of the raw starch film due to the presence of voids on its surface. The swelling process of the starch‐M hydrogel was not significantly affected by changes on the temperature or on pH of the surrounding liquid, indicating the such behavior can be then understood by a diffusional process, resulting from its physical–chemical interactions with the solvent. The values of the diffusional exponent n were on the order of 0.45–0.49 for the range of pHs investigated, demonstrating that the water transport mechanism of starch‐M hydrogel is more dependent on Fickian diffusion, that is, controlled by water diffusion. Such starch‐M hydrogel is a promising candidate to be used in transporting and in preserving acid‐responsive drugs, such as corticoids, for the treatment of colon‐specific diseases, for example, Crohn's disease. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 2567–2574, 2008     

Preparation and Characterization of Poly(N‐Vinylpyrrolidone‐co‐Methacrylic Acid) Hydrogels

In this study, N‐vinylpyrrolidone (VP)/methacrylic acid (MAA) copolymers have been prepared at three different mole percents, the methacrylic acid composition being around 5, 10, 15%. MAA and VP monomer mixtures have been irradiated in ⁶⁰Co‐γ source at different irradiation doses and percent conversions have been determined gravimetrically. ～80% conversion of monomers into hydrogels were performed at 3.4 kGy irradiation dose. These hydrogels were swollen in distilled water at pH 4.0, 7.0, and 9.0. P(VP/MAA) hydrogel which contains 5% methacrylic acid showed the maximum % swelling at pH 9.0 in water. Diffusion of water was found to be of non‐Fickian character. Diffusion coefficients of water in P(VP/MAA) hydrogels were calculated. Initial swelling rates of P(VP/MAA) hydrogels increased with increasing pH and MAA content in hydrogels. Swelling kinetics of P(VP/MAA) hydrogels was found to be of second order. Thermal behavior of PMAA, PVP and P(VP/MAA) hydrogel were investigated by thermal analysis. P(VP/MAA) hydrogel gained new thermal properties and the temperature for maximum weight loss and temperature for half‐life of P(VP/MAA) hydrogel were determined.     

Reinforcement of Self‐Healing Polyacrylic Acid Hydrogel with Acrylamide Modified Microcrystalline Cellulose†

Self‐healing hydrogel such as polyacrylic acid (PAA) hydrogel has attracted increasing attention based on its promising potential applications. However, it usually suffers from low strength especially as mechanical device. Herein, a commercial microcrystalline cellulose (MCC) was modified with acrylamide to graft polyacrylamide (PAM) chains on the particle surface. The acrylamide‐modified MCC (AM‐MCC) was then dispersed in monomer solution of acrylic acid to prepare composite hydrogel. The mechanical properties of the obtained composite hydrogels and the self‐healed hydrogels were carefully measured by compressive and tensile tests, and by dynamic mechanical analysis. Our results demonstrate that introduction of a small amount of AM‐MCC such as 3 wt% can not only reinforce the original hydrogel and the healed hydrogel markedly, but also improve self‐healing efficiency obviously. The analyses indicate that in addition to the reversible multi‐interactions such as hydrogen bonding and ionic interactions, the entanglements between the PAA chains of the hydrogel matrix and the PAM chains grafted on the MCC particles have also played an important role on the improvement in mechanical performances and the healing ability of the hydrogel. Moreover, the responsiveness to exterior ion has been tested to indicate potential application of the composite hydrogel as self‐healable sensor.     

Preparation and properties of superabsorbent containing starch and sodium humate

Starch and sodium humate were utilized as raw material for synthesizing starch‐g‐poly(acrylic acid)/sodium humate (St‐g‐PAA/SH) superabsorbent by graft copolymerization reaction of starch (St) and acrylic acid (AA) in the presence of sodium humate (SH) in aqueous solution. The effect of weight ratio of AA to St, initial monomer concentration, neutralization degree of AA, amount of crosslinker, initiator and SH on water absorbency of the superabsorbent were studied. The swelling rate and swelling behavior in NaCl solution as well as reswelling ability of the superabsorbent were systematically investigated. The results showed that the superabsorbent synthesized under optimal conditions with SH content of 7.7 wt% and St content of 11.5 wt% exhibits water absorbency of 1100 g/g in distilled water and 86 g/g in 0.9 wt% NaCl solution, respectively. Introducing SH into the St‐g‐PAA polymeric network can improved the swelling rate and reswelling capability of the superabsorbent. Copyright © 2008 John Wiley & Sons, Ltd.     

Amphiphilic conetworks. IV. Poly(methacrylic acid)‐l‐polyisobutylene and poly(acrylic acid)‐l‐polyisobutylene based hydrogels prepared by two‐step polymer procedure. New pH responsive conetworks

This article describes the synthesis and characterization of new amphiphilic polymer conetworks containing hydrophilic poly(methacrylic acid) (PMAA) or poly(acrylic acid) (PAA) and hydrophobic polyisobutylene (PIB) chains. These conetworks were prepared by a two‐step polymer synthesis. In the first step, a cationic copolymer of isobutylene (IB) and 3‐isopropenyl‐α,α‐dimethylbenzyl isocyanate (IDI) was prepared. The isocyanate groups of the IB–IDI random copolymer were subsequently transformed in situ to methacrylate (MA) groups in reaction with 2‐hydroxyethyl methacrylate (HEMA). In the second step, the resulting MA‐multifunctional PIB‐based crosslinker, PIB(MA)_n, with an average functionality of approximately four methacrylic groups per chain, was copolymerized with methacrylic acid (MAA) or acrylic acid (AA) by radical mechanism in tetrahydrofuran giving rise to amphiphilic conetworks containing 31–79 mol % of MAA or 26–36 mol % of AA. The synthesized conetworks were characterized with solid‐state ¹³C‐NMR spectroscopy and differential scanning calorimetry. The amphiphilic nature of the conetworks was proven by swelling in both aqueous media with low and high pH and n‐heptane. The effect of varying pH on the swelling behavior of the synthesized conetworks is presented. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1284–1291, 2009     

Synthesis of chiral micelles and nanoparticles from amino acid based monomers using RAFT polymerization

Homopolymers of ^tbutyl acrylate (P^tBuA) and a monosubstituted acrylamide (PAM) having an amino acid moiety in the side chain, N‐acryloyl‐(L )‐phenylalanine methyl ester 1 , have been synthesized by Reversible Addition‐Fragmentation Chain Transfer (RAFT) polymerization. Diblock copolymers of these homopolymers were also synthesized by chain extending P^tBuA with monomer 1 and after modification, using simple acid deprotection chemistries of the acrylate block to afford a poly (acrylic acid) block, an optically active amphiphilic diblock copolymer was isolated. The optically active amphiphilic diblock copolymers, which contain chiral amino acid moieties within the hydrophobic segment, were then self‐assembled to afford spherical micelles which were subsequently crosslinked throughout the shell layer to afford robust chiral nanoparticles. The hydrodynamic diameters (D_h) of the block copolymer micelles and nanoparticles were measured by dynamic light scattering (DLS) and the dimensions of the nanoparticles were determined using tapping‐mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3690–3702, 2008     

Sucrose diacrylate: A unique chemically and biologically degradable crosslinker for polymeric hydrogels

A series of degradable hydrogels based on different vinyl monomers such as acrylamide, sucrose-1′-acrylate, and acrylic acid were synthesized using sucrose-6,1′-diacrylate (SDA) as a crosslinking agent. SDA was prepared by enzymatic transesterification of vinyl acrylate with sucrose in pyridine. Base catalyzed hydrolysis of SDA in aqueous solution was studied as a function of pH. As expected, hydrolysis of SDA was faster at higher pHs such that poly(acrylamide), poly(sucrose 1′-acrylate), and poly(acrylic acid) hydrogels underwent substantial degradation at and above pH 7, 9, and 13, respectively. The degradation was characterized by changes in the swelling ratios of the hydrogels indicating breakage of the crosslinking agent. Degradation of the hydrogels at their chemically stable pHs was studied in presence of enzymes. Enzymes, including pepsin and a fungal Lipase, were able to degrade the poly(acrylamide) hydrogel at pH 4 and 5, respectively. Poly(acrylic acid) hydrogel was degraded in presence of a fungal protease at pH 7.8. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35 : 2221–2229, 1997     

Synthesis of polymers by template polymerization. I. Template polymerization of poly(methacrylic acid) with β‐cyclodextrin

A novel template monomer with multiple methacryloyl groups was synthesized with β‐cyclodextrin by the acetylation of primary hydroxyl groups and the esterification of secondary hydroxyl groups with methacrylic acid anhydride. The average number of methacryloyl groups in the monomer was 11. The radical polymerization of the monomer was carried out with the following initiators: α,α′‐azobisisobutylonitrile, H₂O₂? Fe²⁺ redox initiator, p‐xylyl‐N,N‐dimethyldithiocarbamate (XDC), and α‐bromo‐p‐xylyl‐N,N‐dimethyldithiocarbamate (BXDC). When the concentration of the monomer was less than 4.12 × 10^?3 M, polymerization was limited inside the molecule, and gelation of the system was hindered. For controlled radical photopolymerization with XDC and BXDC, the methacryloyl groups of the monomer were homogeneously polymerized, and poly(methacrylic acid) with a narrow molecular weight distribution was obtained by the hydrolysis of the polymerized products. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3539–3546, 2001     

Synthesis and characterization of synthetic polymer colloids colloidally stabilized by cationized starch oligomers

A method is developed for anchoring enzymatically degraded cationized starch as electrosteric stabilizers onto synthetic latices, using cerium(IV) to create free‐radical grafting sites on the starch. Direct anchoring of debranched starch onto a poly(methyl methacrylate) seed latex yields a latex stabilized by well‐defined oligosaccharides. Using α‐amylase to randomly cleave starch to form (1→4)‐α‐glucans, and a comonomer, N‐isopropyl acrylamide (NIPAM), whose corresponding polymer exhibits a lower critical solution temperature (LCST), creates a means to synthesize block (or graft) oligomers of oligosaccharide and synthetic polymer, which are water soluble at room temperature. Above 30 °C, they become amphiphilic and form self‐emulsifying nanoparticles (sometimes termed “frozen micelles”) from which a synthetic latex is grown after addition of methyl methacrylate, the collapsed NIPAM‐containing entities functioning as a type of in situ seed. This synthesis of stable synthetic latex particles is shown to have a high grafting efficiency. The starch fragments were characterized by ¹H solution‐state NMR before grafting, and ¹³C solid‐state cross‐polarization magic‐angle spinning (CP‐MAS) NMR was used to characterize the starch oligomers actually grafted on the final latex. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 1836–1852, 2009     

A study of the graft copolymerization of methacrylic acid onto starch using the H2O2/Fe++ redox system

Graft copolymerization of methacrylic acid (MetAc) onto potato starch using H₂O₂/Fe⁺⁺ redox system was investigated. The best conditions of the grafting reaction were determined and several variables were studied: initiator and monomer concentrations, time, and temperature. Percent grafting efficiency, percent grafting, percent grafted monomer conversion, and total conversion were obtained. The optimum graft yield was obtained at 7.3 × 10^?3M H₂O₂ concentration and it was favored by increasing the methacrylic acid concentration and reaction time.     

Novel temperature‐responsive water‐soluble copolymers based on 2‐hydroxyethylacrylate and vinyl butyl ether and their interactions with poly(carboxylic acids)

Novel water‐soluble amphiphilic copolymers have been synthesized by free radical copolymerization of 2‐hydroxyethylacrylate with vinyl butyl ether. In water these copolymers exhibit lower critical solution temperature, which depends on the content of hydrophobic vinyl butyl ether units. The interaction between these copolymers and poly(acrylic acid) or poly(methacrylic acid) in aqueous solutions results in formation of interpolymer complexes stabilized by hydrogen bonds and hydrophobic interactions. An increase in hydrophobicity of the copolymers leads to the enhancement of their complex formation ability with respect to poly(acrylic acid) and poly(methacrylic acid). Poly(methacrylic acid) forms stronger complexes with the copolymers when compared with poly(acrylic acid). The complexes exhibit dual sensitivity to pH‐ and temperature and this property may be easily adjusted regulating the strength of interaction. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 195–204, 2006     

Synthesis and characterization of positively charged,alumina‐coated silica/polystyrene hybrid nanoparticles via pickering miniemulsion polymerization

Positively charged, raspberry‐like hybrid nanoparticles, consisting of a polystyrene core and an alumina‐coated silica shell were successfully prepared in a surfactant free system via the radical copolymerization of styrene (St) and different comonomers (acrylic acid, methacrylic acid, and acrylamide) by using a cationic silica sol as the sole emulsifier in Pickering miniemulsion polymerization. The influence of different parameters like pH of the dispersion, comonomer content, and the amount and size of silica nanoparticles on the colloidal stability of the systems, prepared with different comonomers, was examined. The particles' morphology was observed via high‐resolution scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The removal of free silica particles via centrifugation was proved by TEM and SEM, and the content of free and adsorbed silica was quantified via thermogravimetric analysis (TGA). © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

3‐D Interdigitated electrodes for uniform stimulation of electro‐responsive hydrogels for biomedical applications

Stimuli‐responsive hydrogels are continuing to increase in demand in biomedical applications. Occluding a blood vessel is one possible application which is ideal for a hydrogel because of their ability to expand in a fluid environment. However, typically stimuli‐responsive hydrogels focus on bending instead of radial uniform expansion, which is required for an occlusion application. This article focuses on using an interdigitated electrode device to stimulate an electro‐responsive hydrogel in order to demonstrate a uniform swelling/deswelling of the hydrogel. A Pluronic‐bismethacrylate (PF127‐BMA) hydrogel modified with hydrolyzed methacrylic acid, in order to make it electrically responsive, is used in this article. An interdigitated electrode device was manufactured containing Platinum electrodes. The results in this paper show that the electrically biased hydrogels deswelled 230% more than the non‐biased samples on average. The hydrogels deswelled uniformly and showed no visual deformations due to the electrical bias. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2013 , 51, 1523–1528     

Investigation of the radical copolymerization and terpolymerization of maleic anhydride and norbornenes by an in situ 1H NMR analysis of kinetics and by the mercury method: Evidence for the lack of charge‐transfer‐complex propagation

The radical copolymerization of electron‐deficient maleic anhydride (MA) and electron‐rich norbornene (NB) derivatives with 2,2′‐azobis(isobutyronitrile) (AIBN) in dioxane‐d₈ has been monitored in situ by ¹H NMR spectroscopy with free induction decays recorded every 30 min at 60, 70, or 84 °C. The ratios of the monomer pairs were varied in some cases. The NB derivatives employed in this study included bicyclo[2.2.1]hept‐2‐ene (NB), t‐butyl 5‐norbornene‐2‐carboxylate, methyl 5‐norbornene‐2‐methyl‐2‐carboxylate, and ethyl tetracyclo[4.4.0.1^2,5.1^7,10]dodec‐3‐ene‐8‐carboxylate. Decomposition of AIBN, consumption of the monomers, feed ratios, endo/exo ratios, copolymer compositions, and copolymer yields were studied as a function of polymerization time. Furthermore, a homopolymerizable third monomer (t‐butyl methacrylate, methacrylic acid, t‐butyl acrylate, or acrylic acid) was added to the NB/MA 1/1 system, revealing that the methacrylic monomer polymerizes rapidly in the early stage and that the ratio of MA to NB in the terpolymer strongly deviates from 1/1. In contrast, however, the acrylic monomers are more uniformly incorporated into the polymer. Nevertheless, these studies indicate that MA and NB do not always behave as a pair in radical polymerization and disproves the commonly believed charge‐transfer mechanism. Electron‐deficient fumaronitrile was also included in the kinetics study. To further understand the copolymerization mechanism, MA and NB were competitively reacted with a cyclohexyl radical generated by the treatment of cyclohexylmercuric chloride with sodium borohydride (mercury method). A gas chromatographic analysis of the reaction mixtures has revealed that a cyclohexyl radical reacts with MA almost exclusively in competition and that the cyclohexyl adduct of MA essentially accounts for all the products in a mass balance experiment, eliminating a possibility of the formation of an adduct involving the MA–NB charge‐transfer complex. Thus, the participation of a charge‐transfer complex in the copolymerization of MA and NB cannot be important. © 2000 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 38: 3521–3542, 2000     

Surface‐confined photopolymerization of single‐ and mixed‐monomer systems to tailor the wettability of poly(L‐lactide) film

The major objective of this research was to modify the surface characteristics of poly(L ‐lactide) (PLA) by grafting a combination of hydrophilic polymers to produce a continuum of hydrophilicity. The PLA film was solvent cast, and the film surfaces were activated by ultra violet (UV) irradiation. A single monomer or combination of two monomers, selected from vinyl acetate (VAc), acrylic acid (AA), and acrylamide (AAm), were then grafted to the PLA film surface using a UV induced photopolymerization process. The film surfaces resulting from each reaction step were analyzed using ATR‐FTIR spectroscopy and contact angle goniometry. Results showed that AAm dominated the hydrophilicity of the film surface when copolymerized with VAc or AA, while the water contact angles for PLA films grafted with poly(vinyl acetate‐co‐acrylic acid) varied more gradually with feed composition. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6534‐6543, 2006