Free Radical Polymerization Of Acrylamide Research Articles

Inducing pH Responsiveness via Ultralow Thiol Content in Polyacrylamide (Micro)Gels with Labile Crosslinks

Here we present the synthesis and characterization of pH responsive polyacrylamide microgels, synthesized via free radical polymerization of acrylamide and bis (acryloylcystamine) (BAC). The gels were made with ultralow amounts of thiol functional groups incorporated into the polymer. The resulting gel monoliths were mechanically chopped into microgel particles with size distributions ranging from 80 to 200 mum. The gels exhibit an interesting reversible pH-dependent rheological behavior which led to gelling of the colloidal suspension when the pH was increased, and a low-viscosity suspension was obtained when the pH was taken back to the original value. The viscosity of the colloidal system containing MBA crosslinked microgels remained insensitive to pH. This observation motivated further analysis; viscosity measurements of the highly viscous (gel-like) state of the BAC crosslinked microgel colloidal suspension were carried out to further understand the rheological behavior of the colloidal system. Electrophoretic mobility measurements as function of pH of the BAC and MBA crosslinked colloidal polyacrylamide microgel suspensions were performed. The swelling behavior of the microgels for both colloidal systems was also determined as function of pH using static light scattering. This swelling behavior was used to rationalize the observed rheological behavior. The work presented here demonstrates that free thiol groups present within a polymer gel matrix confer pH responsive behavior to the gel in solution. The viscosity of a BAC crosslinked microgel suspension was also measured under reducing conditions. The viscosity of the microgel suspension reduced with time, due to the breakage of the disulfide bonds in the crosslinkers.

Polyacrylamide−Clay Nanocomposite Hydrogels: Rheological and Light Scattering Characterization

The free-radical polymerization of acrylamide in aqueous clay dispersions and the structure of the resulting polymer−clay nanocomposite hydrogels have been investigated by rheometry using oscillatory deformation tests. Laponite was used as clay particles in the hydrogel preparation. The reactions were carried out with and without the presence of the chemical cross-linker N,N‘-methylenebis(acrylamide) (BAAm). In the absence of BAAm, increasing clay concentration from 0.2 to 7% results in 3 orders of magnitude increase of the elastic modulus G‘ of the hydrogels. At a clay concentration of 5% or above, all the reaction systems, with or without BAAm, exhibit similar elastic moduli, indicating that clay mainly determines the rubber elasticity of the hydrogels. The loss factor tan δ was found to be around 0.1, indicating that the nanocomposite hydrogels are much more viscous than the conventional hydrogels. Increasing the amount of clay also increases the viscous, energy dissipating properties of the nanocomposite hydrogels, which are responsible for their improved mechanical properties. Dynamics of the nanocomposite hydrogels was also investigated by dynamic light scattering. The ensemble-averaged scattered intensity of the hydrogels varies nonmonotonically with the clay concentration due to the action of clay both as a cross-linker and as an ionic component during the formation of the nanocomposite hydrogels.

Gelcasting of Aqueous Silicon Carbide / Carbon Black Slurry

This paper describes the investigation of gelcasting of silicon carbide/carbon black aqueous slurry. Aqueous slurries are prepared by using polyvinylpyrrolloidone and tetramethyl ammonium hydroxide as dispersants. Rheological behaviors of the slurries have been studied. Two initiator systems are used to initiate free-radical polymerization of acrylamide in silicon carbide/carbon black aqueous slurry. In order to reduce strong effect of carbon black on inhibiting polymerization of acrylamide, acetylacetone is added into the slurry. The experimental result shows that controllable free-radical polymerization of acrylamide in silicon carbide/carbon black aqueous slurry can be realized by adding small quantity of acetylacetone.

Graft polymerization of acrylamide on chitosan: Copolymer structure and properties

Graft copolymers have been prepared through the free-radical polymerization of acrylamide in water-acetic acid solutions of chitosan in the presence of ammonium persulfate as an initiator. The effect of temperature, pH of a medium, and concentrations of initiator, chitosan, and acrylamide on the grafting kinetics and efficiency has been established. The local concentration of acrylamide in the reaction zone increases due to intermolecular hydrogen bonding between polysaccharide and monomer molecules. Copolymer films are characterized by better mechanical properties compared to those of polysaccharide. Hydrogels with good viscoelastic properties have been obtained when grafting was performed in the presence of N,N-methylenebisacrylamide as a crosslinking agent.

Synthesis, Characterization, and Application of Poly(Acrylamide)/Poly(Vinyl Alcohol) Polyblends

ABSTRACT Free radical polymerization of acrylamide (Aam) in the presence of aqueous solution of three commercial grades of polyvinyl alcohol (PVOH), namely, Vinarol FV (containing very few acetyl groups), Mowiol 4-80 (low viscosity-partially hydrolyzed), and Vinarol STH (medium viscosity-partially hydrolyzed), using ammonium persulfate (AP) initiator resulted in three corresponding PVOH/Aam polyblends. Optimum polymerization conditions were PVOH and AP concentrations, 10% and 0.05 mol/L, respectively; Aam concentration, 50% based on the weight of PVOH; polymerization temperature and time, 70°C and 20 min, respectively; rate of stirring, 200 rpm, at which the three polyblends were prepared at very high polymerization extent ranging from 98.2 to 99.9%. Rheological properties of 10% aqueous solutions of the polyblends at 80°C were studied. The extent of film resolubility of PVOH's and their polyblends follows the descending order: Mowiol®4-80/Aam > Mowiol®4-80 > Vinarol®STH/Aam > Vinarol®STH > Vinarol®FV/Aam > Vinarol®FV. Sizing of gauzy cotton fabric with the polyblends and PVOH's showed that (1) their tensile strength follows the order: Vinarol®STH/Aam > Vinarol®STH > Mowiol®4-80/Aam > Mowiol®4-80 > Vinarol®FV/Aam > Vinarol®FV > Unsized and (2) their desizability follows the order: Mowiol®4-80/Aam > Mowiol®4-80 > Vinarol®STH/Aam > Vinarol®STH > Vinarol®FV/Aam > Vinarol®FV.

Core/shell SiOx@PAM nanospheres from UV‐assisted surface‐initiated free radical polymerization

AbstractThe core/shell SiOx@polyacrylamide (SiOx@PAM) nanospheres were successfully prepared by the in situ surface‐initiated free radical polymerization of acrylamide (AM) from the silica nanoparticles with self‐assembled monolayers (SAMs) of N‐methyl aniline (NMA) in presence of benzophonone via a precipitation polymerization method under the ultraviolet (UV) irradiation. The conversion of monomer (C%) and the percentage of encapsulating (PE%), calculated from the elemental analyses (EA) results, reached 20.9 and 51.0% after 150 min of UV‐irradiation, respectively. It is consistent with the analyses of TGA. Fourier transform infrared (FTIR) analyses also confirmed the formation of the core/shell SiOx@PAM nanospheres. And it was investigated that the silica nanoparticles had been encapsulated with PAM from the X‐ray photoelectron spectrometer (XPS) analyses. The analysis results of transmission electron microscope (TEM) showed that the diameters of the SiOx@PAM nanospheres were in the range of 50–200 nm. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 3433–3438, 2006

Synthesis and swelling characteristics of semi-interpenetrating polymer network hydrogels composed of poly(acrylamide) and poly(γ-glutamic acid)

The swelling behaviours of semi-interpenetrating polymer networks (semi-IPNs) composed of poly(acrylamide) (PAAm) and poly(γ-glutamic acid) (γ-PGA) in water were investigated. The PAAm/γ-PGA semi-IPNs having different molar composition were synthesized by free radical polymerization of acrylamide in the presence of γ-PGA obtained from Bacillus licheniformis bacterium. The swelling behaviours of these semi-IPNs were analysed in buffer solutions at various pH (3, 5, 7 and 10) and two temperature ranges (25 and 37 °C). Swelling rates of all semi-IPNs were relatively high, and they showed sensitivity to both pH and temperature. Maximum values of swelling rates were reached in the range of 33–38 when pH, temperature and poly(γ-glutamic acid) content increase.

On the Hybride Inverse-Emulsion Polymerization of Acrylamide

: The free-radical polymerization of acrylamide (AAm) in the inverse water/monomer/cyclohexane/Tween 85 hybride emulsion was investigated. The effect of emulsifier concentration on the rate of polymerization, desorption of radicals, and colloidal parameters was studied. The homogenization of water, AAm, and emulsifier Tween 85 enabled the formation of stable inverse hybride AAm and N,N’ -methylenebis(acrylamide) (MBA) sterically stabilized emulsions. The polymerization rate vs. conversion curve consists of two nonstationary rate intervals. This is attributed to the variation of monomer concentration at the reaction loci with an increasing conversion. The maximal rate of inverse emulsion polymerization of AAm increases with an increase in the nonionic emulsifier (Tween 85) concentration. The addition of a cross-linker (MBA) slightly increases the rate of polymerization. The average number of radicals per particle (n¯) was observed to be much below 0.5 and to slightly increase with increasing particle size and the addition of MBA. The low value of n¯ was ascribed to the effective desorption of transferred monomeric radicals. The strong decrease of the molecular weight of polyAAm with increasing emulsifier concentration is attributed to the participation of emulsifier on the chain transfer events. The independence of the particle size on the conversion strongly supports the monomer droplet nucleation and the miniemulsion polymerization mechanism. The droplet nucleation and the variation of monomer concentration at the reaction loci can induce the nonstationary-rate intervals.

Synthesis of Polyacrylamide Nanogels by Intramolecular Disulfide Cross-linking

Nondegradable polyamides with protein-like properties were designed and prepared as a copolymeric hydrogel by the free-radical polymerization of acrylamide with a disulfide-containing cross-linking agent, N, N-bisacryloylcystamine. Copolyacrylamides containing pendent thiol groups (BSH) were obtained after reduction of the disulfide bonds in the hydrogel, followed by precipitation in methanol. Ellman's analysis and gel-permeation chromatography (GPC) were used to characterize the copolymer. Redissolution of the copolymer in water at very dilute concentrations, followed by air oxidation under physiological conditions (pH 7.5), resulted in nanoparticles (nanogels). The dilute concentration favored intramolecular disulfide crosslinking in the polymer chain, resulting primarily in a single-chain nanogel. Nanogel formation was confirmed and characterized using GPC, dynamic light scattering and atomic force microscopy. The size of the nanogels ranged from 20–200nm.

Simultaneous in-situ monitoring of parallel polymerization reactions using light scattering; a new tool for high-throughput screening.

A recently introduced technique, simultaneous multiple sample light scattering (SMSLS), was used to monitor parallel polymerization reactions in situ. SMSLS is designed for real-time, high-throughput screening and provides a time-dependent light scattering signature for each reaction, which contains both qualitative and semiquantitative information. Qualitatively, the signature immediately indicates whether the reaction occurs or not, whether there is an initial lag period, and how long the reaction takes until it stops. The signature also provides estimates of the reaction rate and weight average molecular mass M(w), and its shape can help identify mechanistic aspects, for example, controlled versus free radical polymerization, presence of impurities, etc. The method is inherently adapted to small sample volumes and requires no special sample preparation or postpolymerization characterization. The demonstration here involved the free radical polymerization of acrylamide under varying conditions and should be readily applicable to a wide variety of other reactions. Results were cross-checked with multi-detector gel permeation chromatography.

Degradation on polyacrylamides. Part II. Polyacrylamide gels

The stability of polyacrylamide (PAAm) gels, synthesized by free radical polymerization of acrylamide (AAm) and N, N′-methylenebisacrylamide (BIS), was investigated when subjected to thermal and irradiation conditions. The PAAm gels were stable and did not release AAm under fluorescent light. In aqueous solution at 95 °C, a small amount of AAm was observed and it is shown that this is found from the pendant unsaturation of BIS in the gel network. Under UV irradiation, approximately one molecule of AAm is released for every 20,000 repeat monomer units in the gel. Gels were also synthesized from methacrylamide with BIS, AAm with N, N′-methylenebismethacrylamide and AAm with bisacryloyl-piperazine. Their stability is compared to the AAm/BIS gels.

Starch-based biodegradable hydrogels with potential biomedical applications as drug delivery systems

The design and preparation of novel biodegradable hydrogels developed by the free radical polymerization of acrylamide and acrylic acid, and some formulations with bis-acrylamide, in the presence of a corn starch/ethylene-co-vinyl alcohol copolymer blend (SEVA-C), is reported. The redox system benzoyl peroxide (BPO) and 4-dimethylaminobenzyl alcohol (DMOH) initiated the polymerization at room temperature. Xerogels were characterized by 1H NMR and FTIR spectroscopies. Swelling studies were performed as a function of pH in different buffer solutions determining the water-transport mechanism that governs the swelling behaviour. Degradation studies of the hydrogels were performed in simulated physiological solutions for time up to 90 days, determining the respective weight loss, and analyzing the solution residue by 1H NMR. The mechanical properties of the xerogels were characterized by tensile and compressive tests, as well as by dynamo-mechanical analysis (DMA). Dynamo-mechanical parameters are also reported for hydrated samples.

Free-radical Polymerization of Acrylamide by Manganese Peroxidase Produced by the White-rot Basidiomycete Bjerkandera adusta

Acrylamide was polymerized to give polyacrylamide using manganese peroxidase (MnP) produced by the basidiomycete Bjerkandera adusta. The molecular weight of the polymer synthesized by MnP was 155000, higher than those obtained with other reaction systems using horseradish peroxidase and a redox initiator. The 13C-NMR spectrum showed that polyacrylamide was atactic. Electron spin resonance analysis revealed that 2,4-pentanedione added as an initiator was first oxidized to generate a carbon-centered radical, which initiated radical additive polymerization of acrylamide.

Swelling of hydrophobically modified poly(acrylamide) and poly(acrylamide)- co -(acrylic acid) gels in surfactant solutions

A series of hydrophobically modified polyacrylamide and polyacrylamide-co-poly(acrylic acid) gels with systematically varying hydrophobicity were prepared by free-radical polymerization of acrylamide, n-alkylacrylamides (n = 10, 12, and 14), and acrylic acid. The swelling of these gels was examined in water and in both anionic and cationic surfactant solutions. It was found that the gels which incorporated acrylic acid showed extremely high swelling in water. Maximum swelling was observed in gels which incorporated 10 mol% acrylic acid. The swelling of these gels was much less in solutions of both anionic and cationic surfactants than in water. The gels which did not incorporate acrylic acid demonstrated little swelling in water, but showed increased swelling in both anionic and cationic surfactant solutions with increased hydrophobicity of the gel.

Permanganate ion supported over crosslinked polyvinylamine as an oxidising agent for alcohols

Crosslinked polyacrylamide was prepared by the free radical polymerization of acrylamide and divinyl benzene and it was converted to crosslinked polyvinylamine by Hofmann’s degradation reaction using hypobromite. The polyvinylamine so obtained was functionalized with permanganate group to get the polyvinyl ammonium permanganate resin. The catalyst was evaluated to study the oxidation of six alcohols to their corresponding carbonyl compounds in cyclohexane medium. The extent of oxidation reaction with respect to reaction time and the nature of alcohol was studied. The effect of crosslinking the backbone polymer on the reaction was also studied and 5% crosslinking was found to be optimum. The spent polymeric reagent could be regenerated in single step many times with out loss of its capacity. The catalytic resin was insoluble in the medium during oxidation and, therefore, filtration and purification of the products were easy.

Photodegradation of amiloride in aqueous solution

The photodegradation of amiloride hydrochloride in deaerated aqueous solution at 30°C in the pH range 4.5–11.0 was studied by spectrophotometry and reversed-phase HPLC. The neutral form of the drug present in alkaline solution degraded approximately 3-fold faster than the cationic form. The quantum yields for photodegradation of neutral amiloride and its conjugate acid were determined using ferrioxalate actinometry to be 0.023±0.002 and 0.009±0.001, respectively. The initial photoreaction involves dechlorination of amiloride and the major product is N-amidino-3,5-diamino-6-hydroxylpyrazine-carboxamide, established by UV, 1H and 13C NMR, and chemical ionization-mass spectrometry. The mechanism of photolysis is postulated to involve cation radical formation that facilitates the dechlorination step. The photosensitizing activity of amiloride hydrochloride was tested by measuring (a) the rate of oxygen uptake in the presence of singlet oxygen substrates, 2,5-dimethylfuran or l-histidine, and (b) the rate of free radical polymerization of acrylamide, at 30°C in aqueous solution. Photosensitization by amiloride was concluded to occur predominantly via singlet oxygen rather than a free radical mechanism. However, amiloride is a much weaker photosensitizer than other diuretics such as frusemide and hydrochlorothiazide, tested under the same experimental conditions.

A kinetic approach to acrylamide radical polymerization by horse radish peroxidase-mediated initiation

Free-radical polymerization of acrylamide in water at room temperature involves catalysis by horse radish peroxidase to produce radical species from hydrogen peroxide and 2,4-pentanedione through an oxidoreductive pathway. In the presence of the vinylic monomer, initiation takes place, leading to polyacrylamide formation after a long and unreproducible inhibition period. Conversion-time plots are presented, and some kinetic features are compared with results of previous studies of classical acrylamide polymerization.

Cellulose-poly(acrylamide or acrylic acid) interpenetrating polymer network membranes for the pervaporation of water-ethanol mixtures

A new type of interpenetrating polymer network (IPN) pervaporation membranes based on cellulose and synthetic polymers was developed. They were prepared by free-radical polymerization of acrylamide or acrylic acid in the presence (or absence) of the crosslinking agent (allyldextran or N,N′-methylenebisacrylamide) within cellophane films swollen in the reaction mixture. The swelling behavior of these membranes in water–ethanol solutions and their separation characteristics were investigated depending on the polyacrylamide (PAAm) or poly(acrylic acid) (PAA) content in the IPN (Cp) and for ionic cellulose–PAA membranes depending on the degree of neutralization of carboxylic groups and on the type of counterions. IPN membranes were selective over a wide range of ethanol concentration in the feed. The separation factor (α) and the permeation rate (P) significantly improved with increasing Cp in IPN membranes, especially for the cellulose–PAA(K+ form) membranes (for 86% EtOH feed at 50°C, and α and P values reached 1500 and 1.6 kg/m2 h, respectively). The results for ionic and nonionic IPN membranes were compared. The separation characteristics of membranes were in good correlation with their swelling behavior. The α values of the membranes depended on the affinity of the IPN polymer chains functional groups for water. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 69: 761–769, 1998

Free-Radical polymerization of acrylamide by horseradish peroxidase-mediated initiation

Free-Radical polymerization of acrylamide by horseradish peroxidase-mediated initiation

Catalytic chain transfer in polymerization of acrylamide

A catalytic chain-transfer agent based on cobalt phthalocyanine has been used in the free radical polymerization of acrylamide in aqueous acetic acid. The resulting product is an oligomeric poly(acrylamide) whose structure and average chain length has been characterized by proton NMR. This water-soluble oligomer was found to have a terminal double bond and a number-average chain length of approximately 10 to 20 units of acrylamide.