Free Radical Polymerization Of Acrylic Acid Research Articles

Using chitosan nanofibers to synergistically construct a highly stretchable multi-functional liquid mental-based hydrogel for assembling strain sensor with high sensitivity and broad working range

Liquid metal (LM) microdroplets have garnered significant interest as conductive materials for initiating free radical polymerization in the development of conductive hydrogels suited for strain sensors. However, crafting multi-functional conductive hydrogels that boast both high stretchability and superior sensing capabilities remains as a challenge. In this study, we have successfully synthesized LM-based conductive hydrogels characterized by remarkable stretchability and sensing performance employing acrylic acid (AA) to evenly distribute chitosan nanofibers (CSFs) and to subsequently catalyze the free radical polymerization of AA. The resultant polymer network was crosslinked within situ polyacrylic acid (PAA), facilitated by Ga3+ in conjunction with guar gum (GG)-stabilized Ga droplets. The strategic interplay between the rigid, and protonated CSFs and the pliable PAA matrix, coupled with the ionic crosslinking of Ga3+, endows the resulting GG-Ga-CSF-PAA hydrogel with high stretchability (3700 %), ultrafast self-healing, robust moldability, and strong adhesiveness. When deployed as a strain sensing material, this hydrogel exhibits a high gauge factor (38.8), a minimal detection threshold, enduring durability, and a broad operational range. This versatility enables the hydrogel-based strain sensor to monitor a wide spectrum of human motions. Remarkably, the hydrogel maintains its stretchability and sensing efficacy under extreme temperatures after a simple glycerol solution treatment.

One-step synthesis of super-absorbent nanocomposite hydrogel based on bentonite

The nanoparticles of bentonite can be easily synthesized by hydrothermal treatment with microwave-assisted method. The products were characterized by XRD, FTIR, BET, SEM, EDS, and DLS. Results have revealed that the nano-bentonite was in nanometer scale with particles size of 200–300 nm. The SEM analysis of the nano-bentonite dispersion showed that a decrease in agglomeration and surface roughness. The nano-bentonite possessed high surface area (152.4 m2.g−1) and pore volume (0.25 cm3.g−1). Additionally, nanocomposite hydrogels (NB/PAA) were synthesized through the free-radical polymerization of acrylic acid (PAA) in the presence of the as-synthesized nano-bentonite (NB). The presence of NB in hydrogel matrix may improve the tensile strength of hydrogel. The tensile strength of the hydrogel increases from 0.294 to 1.609 MPa when NB content was 1.0% (NB10/PAA). Under the optimum conditions, the nanocomposite hydrogels (NB10/PAA) exhibited high water absorption capacity of 420.0 These findings contribute to the sustainable development and green chemistry.

Highly stretchable, durable, and transient conductive hydrogel for multi-functional sensor and signal transmission applications

Conductive hydrogel has attracted immersive attentions as the most promising candidate for the fabrication of next-generation wearable and soft electronics due to its diverse characteristics. However, simultaneously embodying integrated characteristics, including mechanical durability, electrical sensitivity, environmental stability, and disintegration after service, into a single hydrogel system is still a grand challenge. This work proposed an interfacial engineering strategy to fabricate a transient conductive hydrogel with well-balanced properties, addressing the long-lasting issue of interfacial incompatibility between solid conductive fillers and soft polymer matrix. Using TEMPO-oxidized cellulose nanofibrils (CNFs) as the interfacial stabilizer, a stable CNF encapsulated liquid metal nanoparticles (LMNPs) is synthesized, which can initiate free-radical polymerization of acrylic acid (AA) monomers, forming an entirely physically crosslinked PAA-CNF-LMNPs hydrogel. This hydrogel features several advantages that have not been realized in a single hydrogel, including, environmentally friendly fabrication without addition of chemical initiators and crosslinkers, superb stretchability, satisfied solvent independent conductivity, high strain sensing sensitivity, stable signal transmission, as well as crack insensitive, self-healing, anti-freezing, and transient properties. Owing to these all-round superb properties, this resultant hydrogel is considered a sustainable, durable, and high-performance platform for soft and wearable electronics.

Tough, Repeatedly Adhesive, Cyclic Compression-Stable, and Conductive Dual-Network Hydrogel Sensors for Human Health Monitoring

Hydrogel-based flexible wearable devices have attracted wide attention from researchers due to their great potential application in human–computer interaction, electronic skin, and disease diagnosis. However, the preparation of conductive hydrogels integrating good biocompatibility, excellent mechanical (tensile and compressible) properties, self-adhesive properties, cyclic stretching, and compression stability remains a challenge. By the Schiff base reaction between dialdehyde carboxymethyl cellulose and amino gelatin to form the first layer of the network and by the free-radical polymerization of acrylic acid to form the second layer of the network, a multifunctional conductive dual-network (DN) hydrogel strain sensor was prepared. The composite DN hydrogel has excellent compression properties (the strength reached to 0.12 MPa when the hydrogel was compressed to 50% of its original height), good cyclic compression (≥10 000 times), repeatable adhesion (≥10 times), reliable electrical conductivity, and high sensitivity (gauge factor = 8.1). The biocompatible hydrogel can be used not only to monitor human body movement but also to detect the breathing movement of simulated pig lungs in vitro. Furthermore, the conductive hydrogel was creatively made into a plantar pressure sensor similar to an insole to monitor the stress on the sole of a flatfoot patient, providing a new potential material for flatfoot detection and correction.

Effective removal of heavy metals from water using porous lignin-based adsorbents

Multifunctional composite materials are the key to improving removal capacity and environmental utility. Here, the adsorbent (SLCA) was obtained by free-radical polymerization of acrylic acid with sodium lignosulfonate and citric acid. FTIR, SEM, TGA and XPS characterization methods were used to prove the structure and properties of SLCA adsorbents. The maximum uptake capacities of the optimized SLCA adsorbent is 276 mg g−1 of Cu2+ and 323 mg g−1 of Pb2+, respectively. The Langmuir isotherm and the second-order kinetic model were established to illustrate that the capture of Cu2+ and Pb2+ by the adsorbent belongs to chemisorption on the monolayer. XPS analysis confirmed that complexation and electrostatic attraction are the mechanism of pollutant removal. Not only that, as-resulting adsorbent revealed no significant adsorption cycle efficiency reduction even after 5 runs of sorption-desorption cycle, manifesting that it is of great stability and could be regarded as a promising candidate adsorbent. The purpose of this research was to develop a green lignin-based adsorbent with strong environmental protection and regeneration ability based on cheap polyacrylic resin.

Enhanced elasticity in poly(acrylic acid) gels via synthesis in the presence of high concentrations of select salts.

Poly(acrylic acid) (PAA) gels synthesized via free-radical polymerization of acrylic acid, N,N'-methylenebisacrylamide and high molarities of salts in water exhibit properties markedly different from PAA gels synthesized without salt, even when the latter are incubated in high-molarity salt solutions after gelation. Particularly noteworthy is unusual mechanical behaviour that includes substantially increased elongation, increased modulus, and rapid recovery after strain. The greatest enhancement in viscoelastic behaviour is evident in 2 M LiCl and ZnCl2 samples, with LiCl samples having a modulus of 39 kPa and reaching an extension ratio of 10 and a fracture stress of 135 kPa, and ZnCl2 samples having a modulus of 43 kPa and reaching an extension ratio of 8.5 and a fracture stress of 175 kPa. This enhanced elasticity is thought to be brought about by a combination of coiled but only weakly-entangled PAA chains with phase-separated regions of salt acting as a plasticizer and modulating intermolecular interactions among AA units.

Efficient heavy metal removal from industrial melting effluent using fixed-bed process based on porous hydrogel adsorbents.

High adsorption capacity, fast adsorption kinetics, good reusability and low cost are highly demanded for adsorbents used in practical adsorption process. In this study, a porous double network Jute/Polyacrylic acid (Jute/PAA) gel was prepared using simple free-radical polymerization of acrylic acid in Jute aqueous solution. The high permeability of Jute/PAA hydrogel with about 80 wt% water made internal adsorption sites fully expose to metal ions. The Jute/PAA gel adsorbent could efficiently adsorb heavy metals in melting wastewater, especially Cd2+ and Pb2+. The adsorbent showed very high adsorption capacities of 401.7 mg/g for Cd2+ and 542.9 mg/g for Pb2+. Moreover, the adsorption equilibrium reached within only 10 min for 40 mg/L of Cd2+ and Pb2+ using 1 g/L adsorbent. Meanwhile, the removal efficiencies reached 81.0% for Pb (C0 = 3.825 mg/L), 79.3% for Cd (C0 = 6.075 mg/L), 83.4% for Cu (C0 = 9.325 mg/L), 29.8% for Zn (C0 = 188.6 mg/L), 22.3% for Mn (C0 = 17.05 mg/L), 96.2% for Cr (C0 = 0.25 mg/L) and 99.8% for Fe (C0 = 9.75 mg/L) in melting wastewater using 1 g/L adsorbent in 2 h. In particular, the concentrations of Pb, Cd and Cr decreased below 0.001 mg/L using 4 g/L adsorbent. In the fixed-bed column experiments, the treatment volume of melting wastewater reached 2900 BV (32.8 L) only producing 50 BV (565 mL) eluent. This work develops a highly practical adsorption process based on hydrogel adsorbents for the removal of heavy metals in actual wastewater.

Rheology and Adhesion of Poly(acrylic acid)/Laponite Nanocomposite Hydrogels as Biocompatible Adhesives

Biocompatible nanocomposite hydrogels (NC gels) consisting of poly(acrylic acid) (PAA) and nanosized clay (Laponite) were successfully synthesized by in situ free-radical polymerization of acrylic acid (AA) in aqueous solutions of Laponite. The obtained NC gels were uniform and transparent. Their viscosity, storage modulus G', and loss modulus G″ increased significantly upon increasing the content of Laponite and the dose of AA, while exhibiting a maximum with increasing the neutralization degree of AA. They showed tunable adhesion by changing the dose of Laponite and monomer as well as the neutralization degree of AA, as determined by 180° peel strength measurement. The maximal adhesion was shown when reaching a balance between cohesion and fluidity. A homemade Johnson-Kendall-Roberts (JKR) instrument was employed to study the surface adhesion behavior of the NC gels. The combination of peel strength, rheology, and JKR measurements offers the opportunity of insight into the mechanism of adhesion of hydrogels. The NC gels with tunable adhesion should be ideal candidates for dental adhesive, wound dressing, and tissue engineering.

Rheo-Raman: A Promising Technique for In Situ Monitoring of Polymerization Reactions in Solution

The use of a laboratory-made rheo-Raman device for continuous in situ monitoring of free-radical polymerization of acrylic acid in aqueous solution is reported for the first time. Combining a mixer-type rheometer with a quartz outer cylinder to a Raman spectrometer, this original experimental device has allowed us to overcome three current challenges of polymerization reaction monitoring. First, monomer conversion, polymer formation, and viscosity of reaction medium were continuously monitored with well-defined conditions (composition, temperature, and flow), using Couette analogy. Second, direct correlation between macroscopic viscosity and medium composition was established (accounting for the continuous variation of molar mass distribution). Third, using a mixer-type rheometer provided scalable results, in terms of stirring conditions.

Enzyme immobilization on ultrafine cellulose fibers via poly(acrylic acid) electrolyte grafts

Ultrafine cellulose fiber (diameter 200-400 nm) surfaces were grafted with polyacrylic acid (PAA) via either ceric ion initiated polymerization or methacrylation of cellulose with methacrylate chloride (MACl) and subsequent free-radical polymerization of acrylic acid. PAA grafts by ceric ion initiated polymerization increased with increasing reaction time (2-24 h), monomer (0.3-2.4 M), and initiator (1-10 mM) concentrations, and spanned a broad range from 5.5-850%. PAA grafts on the methacrylated cellulose fibers also increased with increasing molar ratios of MACl to cellulosic hydroxyl groups (MACl/OH, 2-6.4) and monomer acrylic acid (AA) to initiator potassium persulfate (KPS) ratios ([AA]/[KPS], 1.5-6), and were in a much narrower range between 12.8% and 29.4%. The adsorption of lipase (at 1 mg/ml lipase and pH 7) and the activity of adsorbed lipase (pH 8.5, 30 degrees C), in both cases decreased with increasing PAA grafts. The highest adsorption and activity of the lipase on the ceric ion initiated grafted fibers were 1.28 g/g PAA and 4.3 U/mg lipase, respectively, at the lowest grafting level of 5.5% PAA, whereas they were 0.33 g/g PAA and 7.1 U/mg lipase, respectively, at 12.8% PAA grafts on the methacrylated and grafted fibers. The properties of the grafted fibers and the absorption behavior and activity of lipase suggest that the PAA grafts are gel-like by ceric-initiated reaction and brush-like by methacrylation and polymerization. The adsorbed lipase on the ceric ion-initiated grafted surface possessed greatly improved organic solvent stability over the crude lipase. The adsorbed lipases exhibited 0.5 and 0.3 of the initial activity in the second and third assay cycles, respectively.

Cyanoxyl-mediated free-radical polymerization of acrylic acid: Its scope and limitations

This work examines the scope and limitations of the cyanoxyl (·OCN)-mediated free-radical polymerization of acrylic acid (AA) with respect to the criteria of livingness. Cyanoxyl persistent radicals were generated in situ through the reaction between arenediazonium salts (XC6H4NN⊕BF, where X is H, OCH3, Cl, or NO2) and sodium cyanate (NaOCN). This article thoroughly discusses the role played by such oxygen-centered radicals in the polymerization process; it particularly focuses on the influence of the concentration and nature of the diazonium salt, the solvent, and the temperature on features such as the variations of ln([M]0/[M]) versus time (where [M]0 is the initial monomer concentration and [M] is the monomer concentration), the number-average molar mass versus conversion, and the polydispersity versus conversion in cyanoxyl-mediated free-radical polymerizations of AA. Cyanoxyl-terminated samples were used as macroinitiators for the polymerization of methyl methacrylate to generate poly(acrylic acid)-b-poly(methyl methacrylate) block copolymers. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 519–533, 2005

First Nitroxide-Mediated Controlled Free-Radical Polymerization of Acrylic Acid

Controlled poly(acrylic acid) homopolymers were synthesized for the first time by direct nitroxide-mediated polymerization of acrylic acid. The polymerizations were performed in 1,4-dioxane solution at 120 °C, using an alkoxyamine initiator based on the N-tert-butyl-N-(1-diethyl phosphono-2,2-dimethyl propyl) nitroxide, SG1. The kinetics were controlled by the addition of free nitroxide at the beginning of the polymerization and the optimal amount was 9 mol % with respect to the initiator. In this case, whatever the initiator concentration, all polymerizations exhibited the same rate and conversion reached 85−90% within 5 h. Although the rate constant of propagation of acrylic acid is very large, its reactivity is moderated by a low activation−deactivation equilibrium constant between active macroradicals and SG1-capped dormant chains. Various alkoxyamine concentrations were investigated to target different molar masses. At high initiator concentrations, the number-average molar mass, Mn, increased linear...

Novel Family of Thermogelling Materials via C−C Bonding between Poly(acrylic acid) and Poly(ethylene oxide)-b-poly(propylene oxide)-b-poly(ethylene oxide)

Pluronic poly(ethylene oxide)−poly(propylene oxide)−poly(ethylene oxide) (PEO−PPO−PEO) block copolymers are copolymerized with poly(acrylic acid) (PAA) by a one-step free-radical polymerization of acrylic acid with the chain transfer to the Pluronic dissolved in the acrylic acid. Exponential increase of branching and cross-linking in the resulting Pluronic−PAA copolymers is observed at high degrees of conversion of acrylic acid. The solutions show reversible gelation within a narrow temperature range, with a gelled state resembling that of permanently cross-linked gels. Onset of thermogelation in Pluronic−PAA solution coincides with augmentation of light-scattering intensity of large scatterers and approaches the critical micellization temperature of the parent Pluronic. Effects of the overall PEO content and the length of the PPO segment in the parent Pluronic on the properties of copolymers are revealed.

Analysis of drug distribution in hydrogels using fourier transform infrared microscopy.

The purpose of this work was to study solute (drug and protein)/polymer interactions that affect solute diffusion in and subsequent release from swellable dosage forms based on environmentally responsive, pH-sensitive polymer networks. Ionizable pH-sensitive hydrogels were synthesized by free-radical polymerization of acrylic acid (AA) and 2-hydroxyethyl methacrylate (HEMA) with ethylene glycol dimethacrylate as crosslinking agent. The degree of crosslinking and degree of hydrophilicity were controlled by varying the relative concentration of crosslinking agent and comonomer, respectively. The role of solute distribution within the hydrogels as related to the transport behavior was investigated by Fourier transform infrared (FTIR) microscopy. The solute-loaded hydrogels were cryotomed into 4 microns thin sections. The concentration profile of the solute was constructed from the two dimensional intensities measured by monitoring the infrared vibrational band indicative of that compound in the x and y direction. These studies indicated that the model solute, oxprenolol HCl, was evenly distributed throughout the bulk and surface of the hydrogel samples. Solute/polymer interactions were investigated as a function of the polymer composition and swelling media pH. The concentration profiles of oxprenolol HCl solution loaded into PAA and P(AA-co-HEMA) hydrogels were analyzed by scanning electron microscopy by FTIR microscopy. For hydrophilic polymers (hydrogels) containing ionizable pendant groups, the molecular weight between crosslinks, the degree of swelling, and the degree of ionization were altered by local changes in pH and ionic strength. The data demonstrated that it is possible to evaluate the polymer/solute interactions by using FTIR microscopy.

Free-Radical Polymerization of Acrylic Acid in Benzene

Abstract The polymerization of acrylic acid with NO2 in benzene was carried out. The initial rate of polymerization shows first-order dependence on the monomer concentration and half-power dependence on the initiator concentration. The molecular weight of polymers also shows dependence on monomer and initiator concentrations. The overall activation energy of polymerization was found to be about 22.7 kcal/mol. The kinetic mechanism of polymerization is discussed.