Self-assembly of hydrophobic associating polyacrylamide prepared by aqueous dispersion polymerization

Abstract

Hydrophobic associating polyacrylamide (PDH) was prepared via aqueous dispersion polymerization in the presence of ammonium sulfate. In order to dissolve the polymer at high salt solution concentration, a hydrophobic precursor monomer with two cationic heads was synthesized. Upon polymerization, spherical PDH polymer particles were obtained with an average size of about 9.1?µm. The PDH was fully dispersed in water in twenty seconds, leading to a transparent gel. PDH demonstrated superior properties compared to the partially hydrolyzed polyacrylamide, for instance, regarding salt tolerance and shear resistance. Addition of a small amount of an anionic surfactant significantly affected the PDH dispersion viscosity due to the formation of mixed micelles. The viscosity slightly decreased after strong shearing (>500?s^?1), showing excellent shear resistance. These features indicate that the synthesized PDH offers a great potential for application in hydraulic fracturing and enhanced oil recovery.     

Peculiarities of phase transformations in aqueous isopropanol solutions

Peculiarities of phase transformations in aqueous isopropanol solutions are studied in the range from room temperature to −15°C. It is found that solution cooling results in the formation of macroaggregates with regular geometrical shapes, which are dispersed in the liquid phase and directedly move in the field of a temperature gradient. In aqueous isopropanol solutions with concentrations of 10–30 vol %, the aggregates are formed at temperatures of −10 to −15°C. The average aggregate size is several millimeters. Under the action of a temperature gradient, the aggregates move to the region of higher temperatures. At temperature gradients of 1–2 K/cm, the aggregate velocity is 1–2 mm/s. The characters of the motion and interaction of aggregates are very sensitive to the temperature distribution in a solution. After the aggregate motion ceases, crystallization of the liquid phase that initially is outside of the aggregates is observed.     

Ultrafast dynamics in aqueous polyacrylamide solutions.

We have investigated the ultrafast dynamics of aqueous polyacrylamide ([-CH(2)CH(CONH(2))-](n), or PAAm) solutions using femtosecond optical heterodyne-detected Raman-induced Kerr effect spectroscopy (OHD-RIKES). The observed aqueous PAAm dynamics are nearly identical for both M(w) = 1500 and 10 000. Aqueous propionamide (CH(3)CH(2)CONH(2), or PrAm) solutions were also studied, because PrAm is an exact model for the PAAm constitutional repeat unit (CRU). The longest time scale dynamics observed for both aqueous PAAm and PrAm solutions occur in the 4-10 ps range. Over the range of concentrations from 0 to 40 wt %, the picosecond reorientation time constants for the aqueous PAAm and PrAm solutions scale linearly with the solution concentration, despite the fact that the solution shear viscosities vary exponentially from 1 to 264 cP. For a given value of solution concentration in weight percent, constant ratios of measured reorientation time constants for PAAm to PrAm are obtained. This ratio of PAAm to PrAm reorientation time constants is equal to the ratio of the volume for the PAAm constitutional repeat unit (-CH(2)CHCONH(2)-) to the molecular volume of PrAm. For these reasons, we assign the polymer reorientation dynamics to motions of the entire constitutional repeat unit, not only side group motions. Simple molecular dynamics simulations of H[-CH(2)CH(CONH(2))-](7)H in a periodic box with 180 water molecules support this assignment. Amide-amide and amide-water hydrogen-bonding interactions lead to strongly oscillatory femtosecond dynamics in the Kerr transients, peaking at 80, 410, and 750 fs.     

Peculiarities of redox polymerization of methacrolein in aqueous media

The effect of the amount of metabisulfite and of the change (spontaneous or deliberate) in the pH of the medium on the viscosity and structure of the polymers is shown. These data as well as evidence on the structure of the polymers formed in the presence of “foreign” aldehydes suggest that in addition to the polymerization proceeding by the radical mechanism, heterolytic processes occur at the carbonyl group. As a result, structures of the semiacetal ester type are formed in the polymer chains of methacrolein.     

Free radical-induced oxidative degradation of polyacrylamide in aqueous solution

The oxidative main chain degradation of polyacrylamide initiated by ^·OH radicals attacking the polymer in aqueous solution was studied. ^·OH radicals were produced by irradiating dilute polymer solutions with high energy radiation. A bimolecular process (combination of PO₂ radicals) was found to be the rate determining step in the series of consecutive reactions leading to main-chain rupture. This was revealed from results obtained in pulse radiolysis studies using the light scattering detection method. Under the given experimental conditions, the number of radical sites per initial macromolecule exceeded unity with the consequence that intramolecular reactions of PO₂ radicals dominated intermolecular combinations. From both pulse radiolysis and continuous irradiations it was inferred that only a small fraction (about 1%) of the attacking ^·OH radicals initiated main-chain scission.     

GPC analysis of degraded annealed single crystals

Annealed polyethylene single crystals have been degraded with fuming nitric acid, and the molecular weight distribution of the fragments determined by using a gel-permeation chromatograph. Peaks due to chain folding were observed in these distributions as for unannealed single crystals. The peaks moved to lower molecular weight with increasing degradation time. Comparison of the lowest molecular weight peak length after a given degradation time with the low-angle x-ray periodicity before degradation gave information about a disordered surface layer. The thickness of this layer at early states of degradation was dependent solely on annealing temperature, though changes in the layer must have occurred with annealing time, since there was an increase in reaction rate with annealing time. At higher degradation states, the thickness of the layer was dependent solely on the original low-angle periodicity. This has been related to the depth at which some folds are buried beneath the lamellar surfaces. The relevance of these observations to the structure of annealed single crystals is discussed.     

Following the enzymatic digestion of chondroitin sulfate by a simple GPC analysis

We describe the use of gel permeation chromatography (GPC) setup with four size exclusion columns for analysis of enzymatically digested glycosaminoglycans (GAGs). This setup provides information about the molecular weight (Mw) and concentration of all species (low and high Mw) present in the digests in a single measurement. The data about the fraction with high Mw (often omitted in the analysis of GAG digests) provide direct evidence about the mechanisms of action of the enzymes. We proved the feasibility of this methodology by applying it to chondroitin sulfate (CS) substrates with different molecular weight and sulfation pattern and using different enzymes (hyaluronidase and chondroitinase). NMR analysis of the obtained digests fractionated by ultrafiltration confirmed the results obtained by GPC setup and reveal further details about the degradation mechanisms: (i) both enzymes preferentially attack 4-sulfated chondroitin and (ii) additionally to the well documented endolytic activity of hyaluronidase we also observed a low lyase activity for this enzyme reflected in the detected minor exolytic breakage. Finally, we demonstrate that CS with medium molecular weight (12–60 kDa) which is sulfated mainly at 6-position can be obtained in good yields by enzymatic digestion and following ultrafiltration.     

Swelling of polyacrylamide gels in aqueous solutions of ethylene glycol oligomers

Addition of a small amount of ethylene glycol oligomers (OEG), with the number of repeat units y = 2–4, in an aqueous solution leads to the contraction of both linear and cross-linked poly(acrylamide-co-acrylic acid) chains. The results present clear evidence for the screening effect of OEG on the ionic groups of the polymer chains. Measurements indicate that the pre-swollen poly (acrylamide-co-acrylic acid) gels immersed in aqueous OEG solutions are at equilibrium. However, as the molecular weight of OEG increases, these gels cannot attain their equilibrium swelling ratio due to the appearance of non-equilibrium structures. The stability of these structures increases as the initial swelling degree of the gels increases.     

Influence of polymerization initiation rate on permeability of aqueous polyacrylamide gels

It was shown by Weiss and Silberberg in 1975 that polyacrylamide gels prepared by copolymerization of acrylamide and N,N′-methylene bis-acrylamide in water are heterogeneous. A two-phase model developed in 1979 satisfactorily accounted for the permeability of the gels. These gels had been prepared under standard conditions of initiator and activator concentrations and involved precooling of the reaction mixture to 0°C with completion of the reaction at room temperature, a thermal history not very suitable for kinetic analysis. A procedure was, therefore, devised where gels are prepared at room temperature throughout. Much better correlations are then obtained, and it can be shown that the initiation is controlled by the initiator (ammonium persulfate) concentration times the activator (N,N,N′,N′-tetramethylethylene diamine) concentration raised to the 1.5 power. These data, discussed in terms of the two-phase model, show that the initiator concentration directly determines the number of crosslinks in the more dilute, permeability-determining, gel phase. The faster the initiation, the less permeable a gel results. An increase of permeability with overall degree of crosslinking at constant monomer concentration is a feature only of gels prepared at sufficiently low polymerization initiation rates.     

TEMPO-substituted polyacrylamide for an aqueous electrolyte-typed and organic-based rechargeable device

A hydrophilic radical polymer, poly(2,2,6,6-teteramethylpiperidinyloxyl-4-yl acrylamide) (PTAm), was synthesized via oxidation of the corresponding precursor polymer, poly(2,2,6,6-teteramethylpiperidine-4-yl acrylamide). Electrochemical properties of the PTAm layer were characterized in three aqueous electrolytes of sodium chloride (NaCl), sodium tetrafluoroborate (NaBF4), and sodium hexafluorophosphate (NaPF6) to optimize its activity as an organic cathode. The counter anion species significantly affected the capacity and the cycle performance of the PTAm layer. The PTAm layer in the presence of BF4? displayed quantitative redox capacity beyond 1 μm layer thickness and maintained the discharging capacity of 110 mAh g-1 (97% vs. the calculated capacity) even after 1000 cycle charging/discharging, which could be ascribed to its appropriate affinity to the aqueous electrolyte without any dissolution into the electrolyte. A totally organic-based rechargeable cell was fabricated using PTAm and poly(N-4,4’-bipyridinium-N-decamethylene dibromide) as the cathode and the anode, respectively, and the aqueous electrolyte of NaBF4. The cell gave a plateau voltage at 1.2 V both on charging and discharging and an excellent charging/discharging cyclability of >2000 with high coulombic efficiency of >95%.     

Computer analysis of proteins separated by polyacrylamide gradient pore gel electrophoresis

A method for measuring lymph-to-plasma (L/P) protein concentration ratios obtained from protein fractions separated by polyacrylamide gradient gel electrophoresis is presented. A curve-fitting technique is used to decompose lymph and plasma electropherograms containing multiple components into individual components, eliminating protein-protein overlap regions. This allows the concentration of each component in the mixture to be measured accurately, yielding more precise estimates of L/P ratios. This technique consists of three phases. Individual electropherograms are constructed for proteins of various sizes by taking a weighted average of measured electropherograms obtained from the two protein standards closest in size to the protein of interest. Using these generated standard curves, the multicomponent lymph and plasma curves are decomposed into the least number of equally spaced components that yield a good fit. A linear least-squares method is used to do this. Each protein fraction is multiplied by the total measured protein concentration to provide a concentration for each component. Finally, L/P concentration ratios of protein fractions with visible peaks were computed by applying an averaging technique to the equally spaced protein fractions. Plots of sheep lung L/P ratio versus protein size obtained in this manner were compared to L/P ratios obtained using a method of analysis which does not correct for protein overlap. The corrected L/P ratios showed less scatter than the uncorrected curves. Lung lymph data analyzed with the correction method indicated an increased lung microvascular permeability for large proteins following endotoxin infusion, whereas the uncorrected curves were too noisy to support this concept.     

Interactions between inorganic salts and polyacrylamide in aqueous solutions and gels

The swelling of poly(acrylamide) (PAAm) gels and the osmotic pressure of linear PAAm in aqueous solutions were predominantly affected by anion type and increased according to the lyotropic series ranking of sodium halide anions: F^? < (H₂O) < Cl^? < Br^? < I^?. The osmotic pressure of PAAm in all examined salt solutions followed the scaling theory, with an exponent of 2.3 ± 0.1. In solutions of a sodium halide series, the value of the pre‐exponential factor seemed to depend on salt concentration, anion radius, and the apparent “anionic‐portion radius” of the water molecule. This radius, extracted from the literature data, marks a transition point of the anion radius effect. Larger anions increase the osmotic pressure of PAAm more significantly as their concentration increases and vice versa. The effects of the anions on the osmotic pressure of PAAm are related to their preferential interactions with the polymer. Iodide, which increased the osmotic pressure of PAAm with respect to its value in pure water, seemed to preferentially adsorb onto the polymer with a binding constant of K_b = 9.7 ± 2.0 M^?1 determined by isothermal titration microcalorimetry. However, fluoride, which decreased the osmotic pressure, was preferentially repulsed. The mechanisms of attraction and repulsion were attributed to ion‐water‐polymer interactions and the solvent quality of the hydrated ions. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 508–519, 2003     

Peculiarities of the formation of polyacrylamide compound-based polyelectrolyte complexes in the course of the flocculation of clay-salt dispersions

Peculiarities of the formation of polyelectrolyte complexes based on cationic and anionic copolymers of acrylamide having different macromolecule charge densities on the surfaces of kaolin particles in highly concentrated salt solution are investigated. The interactions of the copolymers with the clay particle surface and with each other are studied by electrokinetic and IR spectroscopy methods. The rheological properties of kaolin suspensions are investigated in a salt solution in the presence of the polyelectrolytes. The flocculation ability of the polyelectrolytes and their binary mixtures with respect to clay-salt dispersion is estimated. The mechanism for the formation of polyelectrolyte complexes on the surface of clay particles is discussed. It is shown that the complexation of oppositely charged polyelectrolytes on the surfaces of clay particles intensifies the flocculation of clay-salt dispersions.     

Volatile organic analysis by direct aqueous injection

Gas chromatographic environmental analysis by direct aqueous injection (DAI) was studied for 24 volatile organic analytes (VOAs). Internal standardization was used to determine the precision of analysing these compounds by DAI. Aqueous samples were directly introduced to a gas chromatograph using fused-silica, mega-bore capillary column separation with subsequent full-scan ion trap mass spectral detection. Triplicate injections at seven levels of VOA standard solutions over a 10(3) concentration range were performed using an autosampler set up for on-column injection of 0.2 microl. Comparison of single-ion response curves to triple-ion response curves showed that triple-ion quantitation was more sensitive and precise than single-ion quantitation. Of the 24 VOAs determined at the 20 parts per billion (ppb) level, 19 and 20 were detected by the single-ion calibration and triple-ion calibration, respectively. The weighted and non-weighted regression correlation coefficients, r(2), for the 24 responses curves by the two methods, ranged from 0.910 to 0.998, with 76 of 96 being greater than 0.990. Precision, as measured by per cent relative standard deviation, was shown to be best for later eluting compounds and for higher concentrations. Analysis of an environmental sample by DAI was accomplished in 12 min and indicated the presence of benzene at 80 ppb and chlorobenzene at 2 ppm. This demonstrated the feasibility of applying this technique for screening. Several chlorinated benzenes were also detected, establishing the potential for expanding the method to include higher boiling compounds.     

Thermodynamic properties of aqueous polyacrylamide solutions as a function of pressure and temperature

The viscosities of dilute aqueous solutions of polyacrylamide were measured at temperatures from 20 to 60.4° and pressures up to 150 MPa using a falling-body viscometer. The viscosity coefficient, ν, increases exponentially with increasing pressure at a given temperature and concentration. The rate of increase of the apparent energy of activation. E≠, with pressure becomes more rapid as the concentration of the solutions increases. Intrinsic viscosity, [ν], increases with increasing pressure at a given temperature but almost levels off at pressures above 100 MPa while the Huggins constant, k_H, decreases. The Flory-Huggins interaction parameter, _X1, decreases at a greater rate with increasing pressure as the temperature decreases indicating that the effect of pressure on improving the compatability between the polymer and solvent is greater near the θ-temperature. The second virial coefficient, A₂, was calculated from the intrinsic viscosity data and compared with the results obtained by light scattering technique.     

Anomalous solubility of polyacrylamide prepared by dispersion (precipitation) polymerization in aqueous tert‐butyl alcohol

Polyacrylamide prepared by dispersion (precipitation) polymerization in an aqueous t‐butyl alcohol (TBA) medium is only partially soluble when the TBA concentrations in the polymerization media are in the range 82 vol % < TBA < 95 vol %. Independent experiments with a soluble (linear) sample of polyacrylamide show that the polymer swells sufficiently in the aforementioned media to lower the glass‐transition temperature of the polymer below the polymerization temperature (50 °C). The anomalous solubility has been attributed to the crosslinking of polymer chains that occurs during the solid‐phase polymerization of acrylamide in the swollen polymer particles. It is postulated that some of the radical centers shift from the chain end to the chain backbone during solid‐phase polymerization by chain transfer to neighboring polymer molecules, and when pairs of such radicals come into close vicinity, crosslinking occurs. However, dispersion (precipitation) polymerization in other media such as aqueous methanol and aqueous acetone yields polymers that are soluble. This result has been attributed to the fact that the polymer radical undergoes a chain‐transfer reaction with these solvents at a much faster rate than with TBA, which overcomes the effect of the polymer‐transfer reaction. Even the addition of as little as 5% methanol to a TBA–water mixture (TBA:water = 85:10) gives rise to a soluble polymer. The chain‐transfer constants for acetone, methanol, and TBA have been determined to be 9.0 × 10^?6, 6.9 × 10^?6, and 1.48 × 10^?6, respectively, at 50 °C. © 2001 John Wiley & Sons, Inc. J Polym Sci Part A: Polym Chem 39: 3434–3442, 2001     

Effects of data analysis on accuracy and precision of GPC results

The effects of data imprecision and baseline uncertainties have been investigated by computer simulation of GPC data from a polymer sample with a truncated log-normal molecular weight distribution. If the data are very accurate, as few as five data points can be sampled without serious error in computed molecular weight averages. The number of data points required is much larger, however, if these are taken at equal increments of molecular weight rather than elution volume. The effects of noise can be counteracted by increasing the sampling frequency. Baseline uncertainties present a more serious problem, especially for broad-distribution samples. If the detected signal is too noisy to permit accurate location of the baseline, errors can be minimized by using a second, more sensitive detector to determine the peak start and end. It is very difficult to estimate M?_z and higher molecular weight averages accurately if the noise level is greater than 0.5%.     

The analysis of glycoproteins in cells and tissues by two-dimensional polyacrylamide gel electrophoresis

Two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) was used to identify and analyse subsets of proteins in cells and tissues. The combination of 2-D PAGE and [125I] concanavalin A overlay revealed an extraordinary complexity and diversity in the glycoprotein profiles of different cell types. However, the glycoproteins are not expressed idiosyncratically. Rather, their expression is closely linked to the state of differentiation of a particular cell type. Such glycoproteins can therefore be used to generate antibodies specific for differentiated cells. 2-D PAGE analyses of cellular glycoproteins also revealed a major common glycoprotein of 100 kDa. This was localised to the lumen of the endoplasmic reticulum and is referred to as endoplasmin. The combination of 2-D PAGE with electroblotting and 45Ca overlay revealed that endoplasmin and several other luminal endoplasmic reticulum proteins (reticuloplasmins) are high capacity, low affinity calcium binding proteins which could function as calcium storage proteins in the endoplasmic reticulum. One of these called calreticulin is also found in the sarcoplasmic reticulum. 2-D PAGE and 45Ca overlay has been used to demonstrate the presence of a calcium-binding protein (CP22/sorcin) in the cytosol of rodent multidrug resistant cells. Analyses of murine serum by 2-D PAGE revealed the presence of a novel stress protein serum amyloid P component. These studies illustrate the value of 2-D PAGE when used in combination with detection methods which select specific subsets of proteins such as glycoproteins.     

Characterization of waterlogged wood by NMR and GPC techniques

Anaerobic erosion bacteria can slowly degrade waterlogged wood, causing a loss of cellulose and hemicellulose. During this process, lignin can also be altered. For this reason, the chemical characterization of waterlogged archaeological wood is crucial for both the elucidation of the degradation processes and also the development of consolidation and conservation procedures.The complex structure of wood makes it practically impossible to dissolve wood in its native form in conventional molecular solvents. Ionic liquids can provide a homogeneous reaction medium for wood-based lignocellulosic materials. Highly substituted lignocellulosic esters and phosphite esters can be obtained under mild conditions by reacting pulverized wood dissolved in ionic liquid with either acyl chlorides or dioxaphospholanes in the presence of pyridine. As a result, the functionalized wood develops an enhanced solubility in molecular solvents, allowing for a complete characterization by means of spectroscopic and chromatographic techniques.In this study, archaeological woods and reference sound woods of the same taxa (Quercus and Arbutus unedo), along with the corresponding extracted lignin, were fully characterized by means of phosphorus NMR spectroscopy, two dimensional NMR spectroscopy and GPC analysis. The samples were collected from the Site of the Ancient Ships of San Rossore (Pisa, Italy), where many shipwrecks dating from 2nd century BC to 5th century AD have been discovered.The results highlighted a deeper and faster depolymerization of the polysaccharide matrix against a limited degradation of the lignin fraction. The use of innovative solvent system as the ionic liquid [amim]Cl enables to highlight chemical and morphologic changes in wood composition avoiding further degradation.