Precipitation Polymerization Of Acrylic Acid Research Articles

A Sol-Gel Transition and Self-Healing Hydrogel Triggered via Photodimerization of Coumarin.

Reversible chemical covalency provides a path to materials that can degrade and recombine with appropriate stimuli and which can be used for tissue regeneration and repair. However, designing and preparing efficient and quickly self-healing materials has always been a challenge. The preparation strategies of photoresponsive gels attract a lot of attention due to their precise spatial and temporal control and their predetermined response to light stimulation. In this work, the linear copolymer PAC was synthesized via precipitation polymerization of acrylic acid and 7-(2-acrylate-ethoxylated)-4-methylcoumarin. The coumarin groups on the copolymer PAC side chains provide a reversible chemical cross-linking via photostimulation, which achieves reversible regulation of the gel network structure. The concentration of 18 wt% PAC solution produces gelation under irradiation with 365 nm. In contrast, PAC gel is restored to soluble copolymers under irradiation with 254 nm. Meanwhile, the mechanical and self-healing properties of the gel were also explored. It is demonstrated that the cracks of the gel can be repaired simply, quickly, and efficiently. Furthermore, the PAC copolymer shows an excellent adhesion property based on the reversible sol-gel transition. Thus, the PAC gel has considerable potential for applications in engineering and biomedical materials.

Stimuli-responsive DOX release behavior of cross-linked poly(acrylic acid) nanoparticles

AbstractCross-linked poly(acrylic acid) nanoparticles were synthesizedviadistillation precipitation polymerization of acrylic acid and ethylene glycol dimethacrylate withdifferent molar ratios. Spherical nanoparticles with diameters between 75 and 122 nm were synthesized and exhibited temperature and pH-responsive behaviors. However, this behavior was less pronounced for samples with higher cross-linking degrees. The potential of all nanoparticles as carriers for controlled release of doxorubicin (DOX) anti-cancer drug was examined at pH values of 1.2, 5.3 and 7.4. An obvious alleviation in burst release behavior and the amount of cumulative drug release was seen for all nanoparticles as the pH of the medium and the cross-linking degree of nanoparticle increased. Also kinetics of drug release was studied using mathematical models of zero-order, first-order, Higuchi, Korsmeyer-Peppas and Hixson-Crowell, where Higuchi and Korsmeyer-Peppas models best defined the kinetics of drug release.

Supercritical continuous precipitation polymerization of acrylic acid in a droplet-based millifluidic device

In this work, a high pressure droplet-based millifluidic device was developed to achieve the continuous precipitation polymerization of acrylic acid in a green reaction medium: a supercritical mixture of 10 wt% ethanol in CO2 (15/19.5 MPa and 75 °C). To avoid clogging the tubular reactor of 762 µm ID, a segmented flow of an aqueous solution of monomer dispersed in the supercritical mixture (containing the initiator) was generated. During the reaction, the droplets were used as reservoirs which enable the continuous transfer of the monomer to the CO2-rich phase. This work shows that a large range of molar masses of poly(acrylic acid) (from 20,000 to 120,000 g.mol−1) with low polydispersity index (from 1.35 to 1.70) can be obtained. Due to the rapid transfer of the monomer compared to its conversion and the resulting low monomer concentration in the reactive medium, the molar mass distributions are not dependent on the residence time but rather on the initial monomer and initiator concentrations only. Hence in the investigated experimental conditions, the continuous reactive extraction process helps to achieve the precipitation polymerization without clogging the tubular reactor and in mastering the molar mass distribution. The effect of pressure influencing the molar mass distribution of poly(acrylic acid) as well as the competition between two possible loci of polymerization are also discussed.

Application of online infrared spectroscopy to study the kinetics of precipitation polymerization of acrylic acid in supercritical carbon dioxide

The kinetics of precipitation polymerization of acrylic acid in supercritical CO2 is monitored by in situ FTIR spectroscopy.

Precipitation polymerization of hydrophobically modified polyelectrolyte poly(AA-co-ODA) in supercritical carbon dioxide and solution rheology properties

Hydrophobically modified (HM) polyelectrolytes were prepared by using precipitation polymerization of acrylic acid (AA) and octadecyl acrylate (ODA) in various molar ratios in supercritical carbon dioxide. The product was obtained in the form of a white powder and the micrographs show aggregates of primary particles < 1 μm in size. The effects of polymer concentration, ODA content in polymer, surfactant, shear time, shear rate on the apparent viscosity were investigated. The reason leaded to a significant viscosity enhancement was discussed. Steady-state and oscillatory tests of solution were also investigated. Solution exhibited shear thinning behavior and thixotropy. Polymers contain octadecyl acrylate (3.4 mol%) at 0.2 g/dL behaved as high entanglement structures or association gels, since the modulus G′ were being higher than G″ throughout the frequency range. The comparison of apparent and complex viscosities confirmed the association gel properties.

Modeling of precipitation polymerization II: calculation of macroradicals concentrations in the continuous and dispersed phases

According to Hunkeler model, precipitation polymerization of acrylic acid in organic media takes place simultaneously in the both dispersed and continuous phases. In this research, a model is presented based on mass balances of individual species. Hence, concentrations of macroradicals and polymer chains, in different chain lengths, were calculated in the both phases. Number- and weight-average degrees of polymerization and their distributions were concluded in the both dispersed and continuous phases. Calculation of macroradicals concentration was conducted with quasi-steady state approximation (QSSA) as well as without QSSA (based on the governing differential equations). Macroradical precipitate as soon as reaching to critical chain length. Moreover, precipitation is the main termination reaction in the continuous phase. Polymer with critical chain length is the most populated species in the dispersed phase. Comparison of theoretical and experimental results is in good agreement. QSSA theory gives better results than without QSSA theory because occlusion of macroradicals in the dispersed phase does not occur in the precipitation polymerization of water-soluble monomers in the organic media. This article has proved that the polydispersity index (PDI) of polymer product in the precipitation polymerization of acrylic acid in toluene that follows simultaneous polymerization model is less than that of PDI in the other free radical polymerization methods. Centrifugation method was used to sediment fine polymer particles. The yield of reaction was increased by sedimentation process.

Photoinitiated precipitation polymerization in liquid CO2 : Fast formation of crosslinked poly(acrylic acid-co -methoxy polyethylene glycol acrylate) microspheres

Photoinitiated precipitation polymerization of acrylic acid (AA) and methoxy polyethylene glycol acrylate (MPEGA) was carried out in liquid carbon dioxide using ethanol as cosolvent and trimethylol propane triacrylate (TMPTA) as crosslinker. Monodisperse crosslinked microspheres were obtained with size polydispersity index as low as 1.027. The particle yield rose sharply after irradiation and reached to 52% at 5 min, then gently increased to 65% at 60 min, suggesting that most of microspheres were produced in the first 5 min of irradiation. The particle number increased incessantly till very late stage of reaction, which could be attributed to the direct generation of stable nuclei from the fast crosslinking polymerization instead of oligomer aggregation. The effect of ethanol content, feeding ratio of monomers and crosslinker concentration on the morphologies, size, and dispersity of microspheres has been investigated. X-ray photoelectron spectroscopy showed that the microspheres obtained by this procedure were covered with abundant carbon double bonds. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011

Synthesis, Characterization and Solution Properties of Hydrophobically Modified Polyelectrolyte Poly(AA-co-TMSPMA)

The hydrophobically modified polyelectrolyte was synthesized using precipitation polymerization of acrylic acid and 3-[tris(trimethylsilyloxy)silyl]propyl methacrylate (TMSPMA) in various molar ratios in supercritical carbon dioxide. FT-IR, 1H NMR, capillary viscometry, rotational viscometer, transmission electron microscopy and fluorescence spectroscopy were used to characterize this copolymer. The viscosity of the copolymers showed a strong dependence on pH with a maximum at pH=5.5. Associating morphologies of the copolymer were observed by TEM. Associating morphologies of poly(AA-co-TMSPMA) solution changed from a global structure to a shell-core structure with increasing hydrophobic levels. A solution of sample PAT4 with a shell-core structure had the largest viscosity value. In addition, the critical micelle concentration of copolymer solution, cmc, was determined from the relative viscosity. The critical micelle concentration was further confirmed by fluorescence spectroscopy using 1-pyrenemethylamine hydrochloride, PyMeA⋅HCl, as a cationic fluorescent probe. The cmc was determined from the intensity ratios, the first to the third emission peaks I1/I3, and the excimer to monomer IE/IM ratio of the pyrene probe as a function of concentration.

Particle Formation in Precipitation Polymerization: Continuous Precipitation Polymerization of Acrylic Acid in Supercritical Carbon Dioxide

The morphology of the polymer produced during continuous precipitation polymerization of acrylic acid in supercritical carbon dioxide (scCO2) varied significantly with reaction conditions. Three different morphologies were observed: a coagulum of primary particles with diameters of 100−200 nm, irregular particles with diameters of 5−20 μm, and spheres with diameters of 10−100 μm. To explore the variables that control particle morphology, the glass transition temperature (Tg) of poly(acrylic acid) (PAA) was measured at several CO2 pressures using high-pressure differential scanning calorimetry. Sorption of scCO2 into PAA also was measured at various temperatures and pressures with a quartz crystal microbalance. Chow's equation described the Tg reduction by CO2 quite accurately. Formation of large spherical particles of PAA was favored when the polymer molecular weight was relatively low and when the polymerization temperature was well above Tg.

Kinetics of the precipitation polymerization of acrylic acid in supercritical carbon dioxide: The locus of polymerization

The precipitation polymerization of acrylic acid (AA) has been carried out at 50 and 70 ∘ C in supercritical carbon dioxide ( scCO 2 ) , using a continuous stirred-tank reactor. Three kinetic models are compared with experimental data on the rate of polymerization and the viscosity-average molecular weight. The first model, the “solution polymerization” model, is based on the assumption that all reactions: initiation, propagation, and termination, take place in the fluid phase; no reaction takes place in the polymer phase. In the second model, the “surface polymerization” model, chain initiation is assumed to occur in the fluid phase, whereas chain propagation and termination occur in a thin zone on the surface of the polymer particles. The third model, the “interior polymerization” model, is similar to the “surface polymerization” model, except that chain propagation and chain termination take place uniformly throughout each polymer particle. Monomer is assumed to be in phase equilibrium between the supercritical fluid and the polymerization zone. The surface polymerization and interior polymerization models both provide a much better description of the experimental data than the solution polymerization model. This suggests that a significant portion of AA polymerization takes place in the polymer phase, when scCO 2 is the reaction medium. However, the data do not support a choice between the surface and interior polymerization models.

Continuous precipitation polymerization of acrylic acid in supercritical carbon dioxide: The polymerization rate and the polymer molecular weight

AbstractThe precipitation polymerization of acrylic acid in supercritical carbon dioxide was studied in a continuous stirred tank reactor with 2,2′‐azobis(2,4‐dimethylvaleronitrile) as the free‐radical initiator. The reactor temperature was between 50 and 90 °C, the pressure was 207 bar, and the average residence time was between 12 and 40 min. The product polymer was a white, dry, fine powder that dissolved in water. A wide range of polymer molecular weights (5–200 kg/mol) was obtained. The effects of the operating variables on the polymerization rate and on the polymer molecular weight were evaluated. The observed kinetics suggested that polymerization took place in both the supercritical fluid and the precipitated polymer particles. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 2546–2555, 2005

Precipitation polymerization of acrylic acid in compressed carbon dioxide-cosolvent systems

Precipitation polymerizations of acrylic acid (AA) in compressed carbon dioxide (65 bar) with different cosolvents, acetic acid, ethanol, and tetrahydrofuran, were studied. Analyses by viscosity measurement and differential scanning calorimetry indicate that the cosolvents have a pronounced effect on the properties of the product. Scanning electron microscopy shows that the products progress from microparticles to bicontinuous networks to fibers with the change of cosolvents and reaction conditions. Measurement of the volume expansion (ΔV%) of the liquid phase containing different cosolvents indicates that the miscibility of compressed CO2 with the liquid phase is dependent on the cosolvent. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1876–1880, 2003

Effect of cosolvents on the precipitation polymerization of acrylic acid in supercritical carbon dioxide

The precipitation polymerization of acrylic acid (AA) in supercritical (SC) carbon dioxide with acetic acid and ethanol as the cosolvent were studied at 335K in the range 12–17MPa; 2,2′-azobis(isobutyronitrile) AIBN was used as the initiator. Analysis by viscosity measurement and differential scanning calorimetry (DSC) indicates that the cosolvents have a pronounced effect on the product molecular weight and glass transition temperature (Tg). Scanning electron microscopy (SEM) shows that the products are microparticles, and their sizes are affected by the structure and concentration of the cosolvents. A UV/Vis spectroscopic method was used to study the initiation rate of AIBN. The molecular weights of the products are closely related to the decomposition rate.

Swelling behavior of acrylic acid hydrogels prepared by γ-radiation crosslinking of polyacrylic acid in aqueous solution

Swelling behavior of anionic acrylic acid polyelectrolyte hydrogel synthesized by γ-radiation crosslinking of polyacrylic acid in aqueous solution was investigated. Cross-linked polyacrylic acid (PAA) hydrogel was synthesized using a two-step method. First, uncrosslinked PAA was synthesized by free-radical precipitation polymerization of acrylic acid in benzene. In the second step, PAA was dissolved in aqueous solution, and it was crosslinked with γ-irradiation. The swelling behavior of the gels was studied as a function of the concentration of PAA in aqueous solution during γ-irradiation, radiation dose, and pH of the swelling medium. In a buffered solution of pH 4, the degree of swelling ranged from 30 to 300 for irradiation doses ranging from 5 to 25 kGy, and the swelling was Fickian. On the other hand, in a buffered solution of pH 7 the degree of swelling ranged from 80 to 500 depending on the irradiation dose and the swelling was non-Fickian.

Precipitation polymerization of acrylic acid in toluene. II: mechanism and kinetic modeling

Although the kinetics of the precipitation polymerization of acrylic acid were investigated by a number of researchers, no mechanism has been proposed which considers the reaction in both continuous and dispersed phases. In this article a general mechanism is developed for the precipitation polymerization of acrylic acid in toluene. It is compared with experimental data and is found to predict rate of polymerization and molecular weight reasonably well. The mechanism consists of the initiation, propagation, transfer and termination reaction, which are common to all free-radical polymerizations. It also found that monomer-enhanced decomposition and transfer to monomer are the dominant mechanism for initiation and chain termination, respectively. The kinetic parameters were evaluated against experimental data.

Precipitation polymerization of acrylic acid in toluene. I: synthesis, characterization and kinetics

Acrylic acid was isothermally polymerized by precipitation polymerization in toluene at various monomer and initiator concentrations over the temperature range of 40°C–50°C. 2,2′-azobis (2,4-dimethyl-valeronitrile) was employed as a chemical initiator. The rate of polymerization was found to depend on the monomer and initiator concentration to the 1.7th and 0.6th orders, respectively. The greater than first order dependence on monomer concentration signifies a secondary, monomer-enhanced, decomposition step for the initiator molecules. The approximately 0.5 order dependence of the rate of precipitation polymerization on the initiator concentration indicates that the chain termination process is predominantly bi-macromolecular. The temperature dependence on rate of precipitation polymerization obeys an Arrhenius equation with the activation energy found to be 21.49 kcal/mol. This result agrees well with the literature values of 23.5 and 22.0 kcal/mol obtained for the solution polymerization of partially neutralized acrylic acid (pH=11) and undissociated acrylic acid (pH=1), respectively. The weight average molecular weight of the polymer was found to be independent of conversion, indicating that transfer to the monomer is the chain controlling reaction.

Precipitation Polymerization of Acrylic Acid in Supercritical Carbon Dioxide

We report the successful precipitation polymerization of acrylic acid in supercritical carbon dioxide at pressures ranging from 125 to 345 bar utilizing AIBN as a free radical initiator. Analyses by GPC and SEM indicate that for the pressure range studied there is no appreciable effect on product molecular weight, molecular weight distribution, or particle size or morphology. In addition, effective molecular weight control was demonstrated for precipitation polymerizations of acrylic acid in CO 2 through the use of ethyl mercaptan as a chain transfer agent.

Precipitation polymerization of acrylic acid: Kinetics, viscosity and heat transfer

AbstractThe free‐radical precipitation polymerization of acrylic acid in toluene was studied in an isothermal reaction calorimeter. The polymerization shows an autocatalytic behaviour of the rate of polymerization typical for precipitation polymerizations. The rate of polymerization with respect to conversion can be modeled by taking the volume fraction of the precipitated polymer into consideration.The viscosity of the reaction mixture increases with increasing volume fraction of precipitated polymer. The viscosity runs through a maximum at high conversion. The final viscosity decrease is probably due to shear stress caused aggregation phenomena of the polymer particles. A model is discussed which can describe the increase and decrease of viscosity of the system.By means of reaction calorimetry it is possible to determine the reaction‐sided heat transfer coefficient during polymerization. The comparison of the experimentally determined temperature course of the reaction mixture and the temperature course calculated with a coupled model of the polymerization and the calorimeter shows that the heat‐transfer characteristic changes instantaneously during a small conversion interval at the very beginning of the polymerization.

Modelling the kinetics of the precipitation polymerization of acrylic acid

AbstractA kinetic model for the free‐radical precipitation polymerization of acrylic acid in toluene was developed and verified experimentally by using an isothermal reaction calorimeter. The model predicts the rate of polymerization accurately up to complete conversion in the temperature range of 40 to 60°C.