Facile synthesis of N‐vinylimidazole‐based hydrogels via frontal polymerization and investigation of their performance on adsorption of copper ions

We report a new facile strategy for quickly synthesizing pH sensitive poly(VI‐co‐HEA) hydrogels (VI = N‐vinylimidazole; HEA = 2‐hydroxyethyl acrylate) by frontal polymerization. The appropriate amounts of VI, HEA, and ammonium persulfate (APS)/N,N,N′,N′‐tetramethylethylenediamine (TMEDA) couple redox initiator were mixed together at ambient temperature in the presence of glycerol as the solvent medium. Frontal polymerization (FP) was initiated by heating the upper side of the mixture with a soldering iron. Once initiated, no further energy was required for the polymerization to occur. The dependence of the front velocity and front temperature on the VI/HEA weight ratios were investigated. The pH sensitive behavior, morphology, and heavy metal removal study of poly(VI‐co‐HEA) hydrogels prepared via FP were comparatively investigated on the basis of swelling measurements, scanning electron microscopy, and inductively coupling plasma spectrometer. Results show that the poly(VI‐co‐HEA) hydrogels prepared via FP exhibit good pH sensitivity and adsorption capacity. The FP can be exploited as an alternative means for synthesis of pH sensitive hydrogels in a fast and efficient way. The as‐prepared hydrogels can be applied to remove heavy metals. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 4005–4012, 2010     

Frontal polymerization for smart intrinsic self‐healing hydrogels and its integration with microfluidics

Frontal polymerization (FP) is applied for the synthesis of β‐cyclodextrin/poly(vinylimidazole‐co‐N‐vinylcaprolactam‐co‐acrylic acid) (β‐CD/P(VI‐co‐NVCL‐co‐AA)) copolymers. The dependence of frontal velocity and temperature on the initiator and cross‐linker are discussed. The synthesized copolymers have been characterized by Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The thermo‐pH dual‐stimuli responsive behavior of the hydrogel is determined by swelling measurement at different temperatures and pH values. Besides, the hydrogels show intrinsic self‐healing behavior and their healing efficiency is determined by the mechanical tests. Interestingly, we integrate FP with microfluidic technology, which may realize the execution of FP under continuous condition. Such simple microfluidics‐FP integrated approach has both methodological and practical value for the synthesis of functional materials. This paper mainly presents the synthesis and characterization of β‐cyclodextrin/poly(vinylimidazole‐co‐N‐vinylcaprolactam‐co‐acrylic acid) (β‐CD/P(VI‐co‐NVCL‐co‐AA)) copolymers by using thermal frontal polymerization (TFP). Hydrogels were found to be self‐healing with good mechanical performance and show dual thermo‐pH responsive behavior. Low‐cost, energy‐saving and efficient method of thermal frontal polymerization process was integrated with microfluidics technology to prepare supraball hydrogel. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2018 , 56, 1412–1423     

Facile synthesis of 4-vinylpyridine-based hydrogels via laser-ignited frontal polymerization and their performance on ion removal

We report herein the fabrication of poly(AAM-co-4VP) hydrogels (AAM?=?acrylamide, 4VP?=?4-vinylpyridine) by using laser-ignited frontal polymerization (LIFP) in an easy and rapid way. The appropriate amounts of AAM, 4VP, γ-methacryloxypropyltrimethoxysilane-modified nanosilica, and couple redox initiator of ammonium persulfate/N,N,N′,N′-tetramethylethylenediamine were mixed together in the presence of dimethylsulfoxide as solvent. LIFP was initiated by heating the upper side of the mixture with the laser. Once initiated, no further energy or treatment was required for the following polymerization to occur. A variety of features for the preparation of hydrogels, such as the initiator concentration and the ratio of different monomers, were thoroughly investigated. The morphology and swelling behavior of hydrogels were investigated. For comparison, the hydrogels prepared via traditional thermal frontal polymerization were also presented and discussed. Furthermore, the hydrogels possess absorption capacity towards copper ions, which can be applied to remove heavy metals.     

Synthesis and Characterization of pH‐sensitive Poly(IA‐co‐AAc‐co‐AAm) Hydrogels via Frontal Polymerization

In this work, we report a series of poly(itaconic acid‐co‐acrylic acid‐co‐acrylamide) (poly(IA‐co‐AAc‐co‐AAm)) hydrogels via frontal polymerization (FP). FP starts on the top of the reaction mixture with aid of heating provided from soldering iron gun. Once polymerization initiated, no further energy is required to complete the process. The influences of IA/AAc weight ratios on frontal velocities, temperatures, and conversions on the reaction time are thoroughly investigated and discussed where the amount of AAm monomer remains constant. Fourier transform‐infrared spectroscopy (FTIR), differential scanning calorimetry (DSC), scanning electron microscope (SEM), dynamic mechanical analysis, and the swelling measurement are applied to characterize the as‐synthesized poly(IA‐co‐AAc‐co‐AAm) hydrogels. Interestingly, the swelling ratios of the hydrogels are changed with different IA/AAc contents, and the maximum swelling ratios are ~4439% in water. SEM images describe highly porous morphologies and explain good swelling capabilities. Moreover, the poly(IA‐co‐AAc‐co‐AAm) hydrogels exhibit superior pH‐responsive ability. © 2019 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2019 , 57, 2214–2221     

Facile synthesis of amphiphilic gels by frontal free‐radical polymerization

We report a new facile strategy for quickly synthesizing poly(2‐hydroxyethyl acrylate‐co‐vinyl versatate) amphiphilic gels with excellent physicochemical properties by frontal free‐radical polymerization. The appropriate amounts of 2‐hydroxyethyl acrylate, vinyl versatate (VeoVa 9) and ammonium persulfate initiator were mixed together at ambient temperature in the presence of N‐methyl‐2‐pyrrolidone as the solvent medium. Frontal polymerization (FP) was initiated by heating the wall of the tube with a soldering iron. Once initiated, no further energy was required for the polymerization to occur. The dependence of the front velocity and front temperature on the initiator concentration was investigated. The front temperatures were between 132 and 157 °C, depending on the initiator concentration. The morphology, swelling rate, and swelling behavior of amphiphilic gels prepared via FP were comparatively investigated on the basis of scanning electron microscopy, water contact angle, and swelling measurements. Results show that the amphiphilic gels prepared via FP behave with good swelling capacity both in water and organic solvents. The FP can be exploited as an alternative means for synthesis of amphiphilic gels with additional advantages of fast and efficient way. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 823–831, 2010     

High performance of interpenetrating polymer network hydrogels induced by frontal polymerization

We report the rapid synthesis of hydrogels with interpenetrating polymer networks (IPNs) by frontal polymerization (FP). Appropriate amounts of diacetone acrylamide (DAAM), N-methylolacrylamide (NMA), thermoplastic polyurethane (TPU), N,N′-methylenebisacrylamide (MBAA), and ammonium persulfate (APS)/N,N,N′,N′-tetramethylethylenediamine (TMEDA) were mixed together at ambient temperature. FP was initiated by transitorily heating the upper side of the reactants, and poly(DAAM-co-NMA)/TPU IPN hydrogels were obtained within minutes. The preparation parameters were thoroughly investigated. Moreover, we investigated the morphology, swelling capacity, chemical structure and the mechanical properties of poly(DAAM-co-NMA)/TPU IPN hydrogels, along with those of poly(DAAM-co-NMA) hydrogels without IPN structure for comparison. Interestingly, the mechanical strength of poly(DAAM-co-NMA)/TPU IPN hydrogels is notably improved in comparison with that of poly(DAAM-co-NMA) hydrogels. The results indicate that the IPN structure endows hydrogels with high mechanical strength, and FP can be applied as an alternative means for synthesis of IPN hydrogels with additional advantages of speed and efficiency.     

前端聚合制备多孔聚丙烯酰胺水凝胶——溶剂和引发剂对反应和产物的影响

利用前端聚合结合发泡工艺制备了孔结构可调控的聚丙烯酰胺多孔水凝胶.研究发现溶剂和引发剂浓度变化对聚合前端的移动及形成的产物性能有重要影响.增加溶剂用量,聚合前端的移动速度和聚合前端最高温度下降,产物孔径增大,孔壁变厚,材料吸水溶胀性能降低;增加引发剂浓度,聚合前端移动速度显著加快,最高温度升高,产物的孔体积和溶胀率先增加后减小.     

Frontal polymerization synthesis and characterization of Konjac glucomannan‐graft‐acrylic acid polymers

Konjac glucomannan‐graft‐acrylic acid polymers, used as superabsorbent polymers (SAPs), were synthesized by frontal polymerization (FP). The features of front propagation including front velocity and maximum temperature (T_max) were influenced by the amount of glucomannan, initiator, and environment temperature. The graft copolymer was characterized by FTIR, DSC, and SEM. The amount of crosslinking agent mainly determined the crosslinking degree of SAPs that would affect the water absorbency and microstructure. Water absorbency of SAP was also investigated and most of them displayed high water absorption rate. The aforementioned results allow us to conclude that FP can be considered as a promising method to fabricate SAP for its excellent advantages. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3391–3398, 2009     

A facile pathway for the fast synthesis of colloidal crystal‐loaded hydrogels via frontal polymerization

In this work, a dually sensitive colloidal crystal (CC)‐loaded hydrogel has been synthesized via frontal polymerization (FP) in a facile and rapid way. First, a polystyrene CC film was fabricated by vertical deposition on the inner wall of a test tube. Then, a mixture of acrylic acid (AAc), 2‐hydroxyethyl methacrylate (HEMA), and glycerol along with the initiator and crosslinker was added to this test tube to carry out FP, resulting in the formation of CC‐loaded hydrogel. The influence of the mass ratios of HEMA/AAc on front velocity and temperatures were studied. The swelling behavior, the morphology, and the stimuli‐responsive behavior of the CC‐loaded hydrogels prepared via FP were thoroughly investigated on the basis of swelling measurement, scanning electron microscopy, and reflection spectra. Results show that the as‐prepared CC‐loaded hydrogels exhibit excellent dual sensitivity to both methanol concentrations and pH values with very short response time, which can be observed visually without the aid of instruments. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Frontal copolymerization synthesis and property characterization of starch-graft-poly(acrylic acid) hydrogels

Recently, a considerable amount of research has centered on uniquely structured polymers synthesized through self-propagating frontal polymerization. The obtained polymer materials have better features than those obtained by using the classical batch route. The additional advantages are short reaction times and low cost. This work describes the first frontal polymerization synthesis of a graft copolymer superabsorbent hydrogel of acrylic acid onto starch at high monomer and initiator concentration. The effects of varying the relative amounts of the reaction components on the most relevant parameters relating to frontal polymerization were explored. The front velocity dependence on initiator concentration could be fit to a power function. The temperature profiles were found to be very sharp with a maximum temperature below 150 degrees C, which was responsible for high monomer conversion. The ultimate properties of the product appear to depend on the polymerization front velocity and the temperature. The high-temperature and rapid temperature increase at the polymerization front led to products with interconnected porous structures caused by the evaporation of water. So, a fast-swelling, highly absorbing hydrogel with respect to batch polymerization was obtained.     

Development,characterization, swelling,and network parameters of amino acid grafted guar gum based pH responsive polymeric hydrogels

This study includes the synthesis of graft copolymer (GG-g-PAPA) from N-Acryloyl-L-phenylalanine (APA) and guar gum through free radical polymerization. Then, the novel pH sensitive GG-g-PAPA-cl-(PHEA-co-PAMPS) [GGAH] polymeric hydrogels were synthesized by employing free radical cross-linking polymerization using graft copolymer, 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS), and 2-hydroxy ethyl acrylate (HEA). The GGAH hydrogels were characterized using FTIR and SEM. Swelling studies of GGAH hydrogels were performed in distilled water, pH 1.2, and pH 7.4 solutions. The network and swelling kinetic parameters of GGAH hydrogels are also calculated.     

Synthesis of versatile poly(PMMA‐b‐VI) macromonomer‐based hydrogels via infrared laser ignited frontal polymerization

In this work, poly((PMMA‐b‐VI)‐co‐AA) (MMA = methyl methacrylate; VI = 1‐vinylimidazole; AA = acrylic acid) hydrogels and poly((PMMA‐b‐VI)‐co‐AA)/TPU (TPU = thermoplastic polyurethane) IPN (interpenetrating polymer networks) hydrogels have been fabricated via versatile infrared laser ignited frontal polymerization by using poly(PMMA‐b‐VI) macromonomer as the mononer. The frontal velocity and T_max (the highest temperature that the laser beam detected at a fixed point) can be adjusted by varying monomer weight ratios, the concentration of BPO (BPO = benzoyl peroxide) and the amount of TPU. Moreover, the addition of TPU enhances the reactant viscosity to suppress the “fingering” of frontal polymerization (FP) and decrease T_max of the reaction, providing a new inert carrier (TPU) to assist FP. Through the characterization of Fourier transform‐infrared spectroscopy (FT‐IR), scanning electron microscope (SEM), and differential scanning calorimetry (DSC), the desired structure can be proved to exist in the IPN hydrogels. Furthermore, poly((PMMA‐b‐VI)‐co‐AA)/TPU IPN hydrogels possesses more excellent mechanical behaviors than hydrogels without IPN structure. Besides, the poly((PMMA‐b‐VI)‐co‐AA) hydrogels present splendid sensitive properties toward substances of different flavor including sourness (CA, citric acid or GA, gluconic acid), umami (SG, sodium glutamate), saltiness (SC, sodium chloride), sweetness (GLU, glucose), enabling their potential as artificial tongue‐like sensing materials. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 1210–1221     

Fast fabrication of superabsorbent polyampholytic nanocomposite hydrogels via plasma‐ignited frontal polymerization

We report the facile synthesis of poly(VI‐co‐MAA) superabsorbent polyampholytic hydrogels (VI = N‐vinylimidazole, MAA = methacrylic acid) via plasma‐ignited frontal polymerization (PIFP). On igniting the top surface of the reactants with air plasma, frontal polymerization occurred and poly(VI‐co‐MAA) hydrogels were obtained within minutes. The preparation parameters were investigated, along with swelling capacity, morphology, and chemical structures of poly(VI‐co‐MAA) hydrogels. Interestingly, the hydrogels are superabsorbent in water and show ampholytic characteristic toward pH. Moreover, the hydrogels are able to capture cationic dyes through electrostatic interaction, offering the potential for further development as dye adsorbents for water purification. In addition, nanocomposite hydrogels were obtained by embedding quantum dots (carbon dots or CdS nanocrystals) into the polymer matrix, which endows the nanocomposite hydrogels with favorable fluorescence and potential applications in bioimaging and biosensing. The results indicate that FP can be applied as an alternative means for facile synthesis of multifunctional hydrogels with additional efficiency and energy‐saving. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 912–920     

Exhaustive analysis of frontal copolymerization of functionalized monovinyl and divinyl monomers

A series of copolymers of 2-hydroxyethyl methacrylate (HEMA)/glycidyl methacrylate (GMA) and ethylene dimethacrylate (EGDM) were synthesized by frontal polymerization (FP). This study was conducted to investigate the effect of crosslink density, type and concentration of initiator, the use of a complex initiator system, porogen, and diluent on the most relevant parameters of FP, such as sustainability of the front, temperature profile, front velocity, and yield. The products were also characterized for intruded pore volume, pore-size distribution, epoxy-functionality number, and surface morphology. Higher crosslink densities (CLDs) and initiator concentration produced higher front velocities, whereas no trend in front temperature was noted. A complex initiation system was effective in stabilizing and increasing the polymerization yield. Relative to suspension polymerization (SP), FP products synthesized without a solvent were microporous, whereas micro-to-macroporous products were obtained in the presence of a solvent (for HEMA-EGDM polymers). We also present, explain, and discuss the exotic patterns observed under a microscope. We observed two basic types of spatial patterns, namely, planar and nonplanar patterns. The type of planar pattern observed under scanning electron microscopy (SEM) has a spatial impulse that appears as a loop followed by regular periodic motion in the radial and axial directions. This behavior gives rise to a repeating pattern that is a few microns thick. Also, nonplanar patterns, namely, layered concentric rings and winding staircase patterns, were observed under SEM.     

Adsorption of poly(N-isopropylacrylamide-co-4-vinylpyridine) onto core-shell poly(styrene-co-methylacrylic acid) microspheres

Adsorption of the thermoresponsive copolymer of poly(N-isopropylacrylamide-co-4-vinylpyridine) (PNIPAM-co-P4VP) onto the core-shell microspheres of poly(styrene-co-methylacrylic acid) (PS-co-PMAA) is studied. The core-shell PS-co-PMAA microspheres are synthesized by one-stage soap-free polymerization in water. The copolymer of PNIPAM-co-P4VP is synthesized by free radical polymerization of N-isopropylacrylamide and 4-vinylpyridine in the mixture of DMF and water using K₂S₂O₈ as initiator. Adsorption of PNIPAM-co-P4VP onto the core-shell PS-co-PMAA microspheres results in formation of the composite microspheres of PS/PMAA-P4VP/PNIPAM. The driven force to adsorb the copolymer of P4VP-co-PNIPAM onto the core-shell PS-co-PMAA microspheres is ascribed to hydrogen-bonding and electrostatic affinity between the P4VP and PMAA segments. The resultant composite microspheres of PS/PMAA-P4VP/PNIPAM with surface chains of PNIPAM are thermoresponsive in water and show a cloud-point temperature at about 33 °C.     

Synthesis of poly(<Emphasis Type="Italic">N</Emphasis>-methylolacrylamide)/polymethylacrylamide hybrids via frontal free-radical polymerization

In this study, poly(N-methylolacrylamide)/polymethylacrylamide (PNMA/PMAA) hybrids were produced successfully by frontal free-radical polymerization at ambient pressure. In a typical run, the appropriate amounts of reactants (N-methylolacrylamide, NMA; methylacrylamide, MAA) and initiator (ammonium persulfate) were dissolved in dimethyl sulfoxide at ambient temperature. Frontal polymerization (FP) was initiated by heating the wall of the tube with a soldering iron, and the resultant hot fronts were allowed to self-propagate throughout the reaction vessel. Once initiated, no further energy was required for polymerization to occur. The dependences of the front velocity and front temperature on the initiator concentration, reactant dilution, and NMA/MAA components were thoroughly investigated. The front temperatures were between 69 and 116 °C, depending on the persulfate concentration. We have also investigated the FP of PNMA/PMAA hybrids with N-methyl-2-pyrrolidone as solvent. Results show that FP can be exploited as a means for the preparation of PNMA/PMAA hybrids with the potential advantage of higher throughput compared to the traditional mode.     

Micelle-assisted synthesis of PANI nanoparticles and application as particulate emulsifier

Well-defined water-dispersible polyaniline (PANI) nanoparticles were synthesized by in situ chemical oxidative polymerization of aniline in the presence of an amphiphilic P(AMPS-co-VM) copolymer micelle. P(AMPS-co-VM) copolymer was prepared by the free radical polymerization of 7-(4-vinylbenzyloxyl)-4-methyl-coumarin (VM) and 2-acrylamido-2-methyl-1-propanesulfonic acid (AMPS) which can self-assemble into micelles in aqueous solution. Here, P(AMPS-co-VM) copolymer micelle is used not only as soft template but also as acid dopant in our reaction system. The structure, size, and morphology of PANI nanoparticles were characterized by various experimental techniques. It is found that the morphology and the size of the PANI nanoparticles strongly depend on the molecular characteristics of the P(AMPS-co-VM) copolymer. The synthesized PANI nanoparticles behaved as particulate emulsifier for the stabilization of oil-in-water emulsions.     

Facile synthesis of poly(hydroxyethyl acrylate) by frontal free‐radical polymerization

We report the first synthesis of poly(hydroxyethyl acrylate) (PHEA) without solvent by free‐radical frontal polymerization (FP) at ambient pressure. In a typical run, the appropriate amounts of reactant (hydroxyethyl acrylate) and initiator (1,1‐di(tert‐butylperoxy)‐3,3,5‐trimethylcyclohexane) (Luperox 231) were mixed together at ambient pressure. FP was initiated by heating the wall of the tube with a soldering iron, and the resultant hot fronts were allowed to self‐propagate throughout the reaction vessel. Once initiated, no further energy was required for polymerization to occur. To study the macrokinetics, we also produced PHEA frontally with ammonium persulfate as initiator and dimethyl sulfoxide as the solvent. The dependences of the front velocity and front temperature on the initiator concentration and reactant dilution were investigated. The front temperatures were between 124 and 157 °C, depending on the ammonium persulfate concentration. Thermogravimetric analysis indicates that PHEA prepared by FP with ammonium persulfate as initiator had higher thermal stability than solvent‐free frontally prepared PHEA with Luperox 231 as initiator. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 873–881, 2007     

Frontal polymerization synthesis and drug delivery behavior of thermo-responsive poly(N-isopropylacrylamide) hydrogel

Thermo-responsive hydrogels of poly(N-isopropylacrylamide) (PNIPAm) were prepared by fontal polymerization and investigated as a temperature-triggered delivery device for the model drug aspirin. The influence of relative amount of reactant components on the feature of the polymerization front was studied. Furthermore, aspirin was loaded into hydrogels prepared by fontal polymerization method and classical polymerization, respectively, and its release characteristics were determined under different temperature conditions (25 °C and 37 °C). The drug storages and kinetic parameters for two hydrogels indicated that drug-loading capacity and drug release of frontal polymerization (FP) hydrogel were improved as compared with the classical polymerization (CP) one. Scanning electronic microscope and differential scanning calorimetry (DSC) results could account for these improvements in drug delivery for FP hydrogel. The above results indicate that FP can be an alternative method for the preparation of PNIPAm hydrogels used as drug delivery devices with less time consuming and easier protocols.     

Synthesis and characterization of nano-sized poly[(butyl acrylate)-co-(methyl methacrylate)-co-(methacrylic acid)] latex via differential microemulsion polymerization

Poly[(butyl acrylate)-co-(methyl methacrylate)-co-(methacrylic acid)] latex particles were synthesized via differential microemulsion polymerization. The effect of initiator type and methacrylic acid incorporation were investigated. The initiator type could significantly affect the particle size and the molecular weight of the resulting polymer and 2,2′-azobisisobutyronitrile produced the smallest particle size. The incorporation of methyl methacrylate (MAA) in the copolymer and terpolymer structures was confirmed by FTIR and NMR spectroscopy, and DSC in that the carbonyl peak of carboxylic acid at 1,700 cm^?1 in the FTIR spectrum was observed when the MAA amount was high enough, the peak areas at 0.9 ppm in the NMR spectrum confirmed the participation of MAA from the increasing proton signals and the glass transition temperature and polarity of the polymer increased when the MAA amount was increased. This supported that the MAA was incorporated into the polymer chains. MAA was found to produce a vitrification effect during the polymerization.