Hydration of poly(acrylic acid) sodium salts

Summary Drying and water uptake of poly(acrylic acid) sodium salts with different degrees of neutralization were studied. The slowing down of drying speed in solid state was not due to Tg but due to the difficulty of the release of water molecule bound to two metal carboxylates or carboxyls. The equilibrium water uptake remained almost constant below 33 % neutralization, whereas it increased linearly with neutralization beyond 33 %. This was explained by the appearance of vacant sites in octet coordination.     

Density measurements of poly(acrylic acid) sodium salts

Summary Density measurements of poly(acrylic acid) sodium salts (PANa) with different degrees of neutralization and water contents are presented. The apparent partial molar volumes of polymer, V ₂ ^* , and the partial molar volumes of water, V₁, were calculated from the densities. The values of V ₂ ^* decreased with increasing water content and eventually leveled off. The values of Vj, which at low water contents were much smaller than that of free water increased with increasing water content and reached that of free water, showing consequently the appearance of free water. Before reaching the final value of free water, the data indicated the formation of primary and secondary hydration shells. The structure of primary hydration was suggested to be of octet coordination in which carboxyl oxygen atoms participate.     

Pulsed NMR study on the hydration of poly(acrylic acid) salts

Summary Pulsed NMR was applied to measure the spin-lattice (T₁) and spin-spin (T₂) relaxation times of the equilibrium water absorbed in poly(acrylic acid) lithium salt, sodium salt, and potassium salt. T₁ and T₂ relaxation time curves for the samples of lithium and sodium salts studied showed single phase behavior, but the sample of potassium salt exhibited two-phase behavior, indicating the existence of water fraction of higher mobility.     

Hydration of poly(acrylic acid) lithium salts

Summary Drying and water uptake of poly(acrylic acid) lithium salts with different degrees of neutralization were studied. Though the equilibrium water uptake increased with increasing neutralization %, the slope of the plot above ca. 33 % neutralization was greater than that below this neutralization %.     

Hydration of poly(acrylic acid) potassium salts

Summary Drying and water uptake of poly(acrylic acid) potassium salts with different degrees of neutralization were studied. The slowing down of drying speed in solid state was not due to Tg but due to the difficulty of the release of water molecule bound to two metal carboxylates or carboxyls. The equilibrium water uptake decreased below 25% neutralization, whereas it increased linearly with neutralization beyond 25%. The bending in the plot of equilibrium water uptake was explained by the appearance of vacant sites in bodycentered cubic coordination. The initial decrease was attributable to the sum of the two opposite effect, that is, the decrease of free carboxyl groups and the increase in dielectric nature. The results were discussed in connection with those for sodium salts described in the preceding paper.     

Properties of bound water in poly(acrylic acid) and its sodium and potassium salts determined by differential scanning calorimetry

The thermal transitions occurring in poly(acrylic acid) and its sodium and potassium salts were investigated over a large range of water content using differential scanning calorimetry at temperatures below the normal melting temperature of water. The bound water was identified as nonfreezing (type I), freezing with a constant melting temperature (type II), and freezing with a melting temperature dependent on the water content (type III). The transition temperatures of the freezing states of the water were determined. Two constant melting temperatures were observed for the type II water in the sodium and potassium polyacrylates, while a single transition of this type was observed for poly(acrylic acid). The sodium polyacrylate absorbed more water in the nonfreezing state than the potassium polyacrylate, and both polyelectrolytes absorbed about three times as much water in this state as the nonionic poly(acrylic acid). The effects of water content on the occurrence of an exotherm at low temperature in the melting scans of the polyelectrolytes are described.     

Superabsorbent poly(acrylic acid) complex

Acrylic acid and crosslinking agent [poly(ethylene glycol)-diacrylate or divinylbenzene] were copolymerized in benzene in the presence of layered sodium silicate (δ-Na₂Si₂O₅) powder. The resultant poly(acrylic acid) complex shows large water absorbability, for which dependency on crosslinking degree was investigated. © 1996 John Wiley & Sons, Inc.     

Synthesis and characterization of new poly(butadiene-co-acrylic acid(g) acrylic acid) and poly(butadiene(g) acrylic acid)

Synthetic crosslinked polymers from oligomers of butadiene-co-acrylic acid (Mw 5000) or oligomers of butadiene (Mw 6000) and acrylic acids were obtained after grafting reactions using varying reactant ratios. Characterization of the new crosslinked polymers were carried out by use of FTIR, H-NMR, and ¹³C-NMR in the solid state and also with the swollen products in D₂O, DMF D7, or DMSO D6. Determinations of swelling in distilled water for the different synthesized hydrogels showed increase in the V/Vo ratios as the concentrations of anions (carboxylate) became higher. These values were sensitive to different pH values and changes in the concentrations of electrolytes. Different behavior was observed for the polymers obtained from mass and from synthesis in benzene. SEM analysis of the surfaces of the polymers obtained in mass showed a fibrous structure (with lower contents of carboxylic groups, and more swellable and with greater capacity to retain albumin). A porous surface was observed for products obtained in benzene (with higher content of carboxyl groups and capacity to retain cations such as copper and malachite green).     

Preparation of polyacrylamide aqueous dispersions using poly(sodium acrylic acid) as stabilizer

High‐solids, low‐viscosity, stable polyacrylamide (PAM) aqueous dispersions were prepared by dispersion polymerization of acrylamide in aqueous solution of ammonium sulfate (AS) using poly (sodium acrylic acid) (PAANa) as the stabilizer, ammonium persulfate (APS) or 2,2′‐Azobis (N,N′‐dimethyleneisobutyramidine) dihydrochloride (VA‐044) as the initiator. The molecular weight of the formed PAM, ranged from 710, 000 g/mol to 4,330,000 g/mol, was controlled by the addition of sodium formate as a conventional chain‐transfer agent. The progress of a typical AM dispersion polymerization was monitored with aqueous size exclusion chromatography. The influences of the AS concentration, the poly(sodium acrylic acid) concentration, the initiator type and concentration, the chain‐transfer agent concentration and temperature on the monomer conversion, the dispersion viscosity, the PAM molecular weight and distribution, the particle size and morphology were systematically investigated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

The intrinsic viscosity of poly(acrylic acid) and partially neutralized poly(acrylic acid) by isoionic dilution

The isoionic dilution method has been used to measure the intrinsic viscosity, [η], of a poly(acrylic acid) (PAA) sample as a function of neutralization degree, i, at low ionic strength, I = 1.0 × 10. The results obtained for the counterion activity are in close agreement with Manning's theory for counterion condensation. The influence of the ionic strength, I, on [η] and on the Huggins coefficient, k', was also examined and the exponents of the scaling laws relating these two parameters with I were found.     

Ultrasonic degradation of poly(acrylic acid)

The ultrasonic degradation of poly(acrylic acid), a water‐soluble polymer, was studied in the presence of persulfates at different temperatures in binary solvent mixtures of methanol and water. The degraded samples were analyzed by gel permeation chromatography for the time evolution of the molecular weight distributions. A continuous distribution kinetics model based on midpoint chain scission was developed, and the degradation rate coefficients were determined. The decline in the rate of degradation of poly(acrylic acid) with increasing temperature and with an increment in the methanol content in the binary solvent mixture of methanol and water was attributed to the increased vapor pressure of the solutions. The experimental data showed an augmentation of the degradation rate of the polymer with increasing oxidizing agent (persulfate) concentrations. Different concentrations of three persulfates—potassium persulfate, ammonium persulfate, and sodium persulfate—were used. It was found that the ratio of the polymer degradation rate coefficient to the dissociation rate constant of the persulfate was constant. This implies that the ultrasonic degradation rate of poly(acrylic acid) can be determined a priori in the presence of any initiator. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A novel foaming approach to prepare porous superabsorbent poly(sodium acrylic acid) resins

A system composed of surfactant and foam stabilizer is used in preparing porous superabsorbent resins (SARs) of poly(sodium acrylic acid) (PAA‐Na), which is obtained by free‐radical solution polymerization of partially neutralized acrylic acid with mechanical agitation of eggbeater. Different types of surfactant, including anionic surfactant sodium n‐dodecyl benzene sulfate (SDBS), cationic surfactant cetyltrimethyl ammonium bromide, and nonionic surfactant alkylphenols poly(oxyethylene) (OP‐10), are used as blowing agent to produce pores by mechanical agitation, and triethanolamine (TEA) is used to act as foam stabilizer agent. The results show that a synergistic effect of SDBS with TEA is obtained and the packing density is decreased, which could be proved by the clearly porous morphology, and the water absorbing capacity of SARs is enhanced. As a result, such method can get PAA‐Na SARs without any organic solvents, which provides an environmentally beneficial way to prepare SARs for hygiene and biomedical products. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015 , 132, 41298.     

Thermal analysis of poly(acrylic acid)/poly(oxyethylene) blends

Blends between poly(acrylic acid) and two different poly(oxyethylenes), (1) polyethylene glycol (PEG-1000) and (2) poly(oxyethylene) (20) sorbitan monooleate (Tween-80), were studied by differential scanning calorimetry. The glass transition temperatures, T_g, of the various compositions of these blends were found to follow Fox's equation. At room temperature, blends containing no more than 60% PEG-1000 were amorphous and exhibited only a single glass transition. For these blends with PEG-1000, the glass transition temperatures for the annealed samples were higher than for the quenched samples due to the formation of a PEG crystalline phase. It was also found that addition of an amorphous polymer such as poly(acrylic acid) significantly reduced the degree of crystallinity of a semicrystalline polymer such as poly(oxyethylene). The Tween-80 systems did not show phase separation at room temperature. The compatibility between this poly(acrylic acid) and this poly(oxyethylene) was attributed to hydrogen bonding and to the lower crystalline lattice energy of this poly(oxyethylene) through its effect on its ideal solution solubility. © 1993 John Wiley & Sons, Inc.     

Degradation of aqueous poly(acrylic acid) and its sodium salt solutions by high-speed stirring

Poly(acrylic acid) and 100% neutralized poly(acrylic acid) in pure water were stirred at 30°C at 30,000 rpm with a T. K. Homomixer at polymer concentrations ranging from 2% w/v to 0.0025% (25 ppm) for 2 hr to investigate the effect of polymer chain conformation on chain scission by high-speed stirring. After 2 hr of stirring at low concentration, intrinsic viscosity measured in 1.00 mole/1. NaCl solution at 30°C for 100% neutralized polymer was lower for the polymer which was stirred after 100% neutralization than for the one before 100% neutralization, showing that expanded polymer chains were more easily ruptured.     

Interpolymer complexation between poly(ethylene oxide) and poly(acrylic acid)

Summary Solution and solid state properties of the interaction between poly(acrylic acid) and poly(ethylene oxide) have been studied in the presence and absence of CaSO₄ in water or in methanol systems. The association in solution has been investigated by viscosity measurements and NMR spectroscopy. The solid state of the systems has been studied using DSC, IR, X-RAY and 13-C-CPMAS-NMS. Complex formation is also clearly indicated.     

Primary study of novel poly(acrylic sodium)/poly(ether sulfone) composite ultrafiltration membranes (I) the preparation of composite membrane

The poly(acrylic sodium) (PAS)/poly(ether sulfone) (PES) composite ultrafiltration membranes were prepared by coating PAS membrane solution on PES support membrane. The effects of substrate membrane, the composition of PAS solution such as PAS concentration, the choice of the solvent and the additive, and the thickness of PAS active layer on the performance of the composite membranes were extensively investigated. The experimental results have indicated the optimal PAS/PES composite membranes, containing a PES substrate with MWCO of 70,000, together with a PAS top layer having a thickness of about 20 μm, were tested at room temperature and under the pressure of 0.6 MPa with the mass concentration of 0.005 g/L poly(ethylene glycol) (PEG) (Mw = 1000 g/mol) solution, a flux of 32.6 L/(m² h) and a rejection of 92.2% were obtained, which are superior to those of the common commercial membranes reported.     

Polypropylene fibers grafted with poly(acrylic acid)

An effective method for the grafting of poly(acrylic acid) on polypropylene fibers has been developed, using diphenyl and a dispersing agent (NNO) in the grafting bath as additives to facilitate the grafting process. The method makes it possible to obtain high grafting degrees of poly(acrylic acid) on polypropylene fibers with a minimal quantity of homopolymer as a side product. The effect of grafting degree on the moisture absorption and swelling of the modified fibers has been examined and described with mathematical equations. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 2295–2299, 2002     

Spatial inhomogeneity in poly(acrylic acid) hydrogels

The crosslink density distribution in gels known as the spatial gel inhomogeneity has been investigated in poly(acrylic acid) (PAAc) gels with the static light scattering measurements. PAAc gels were prepared at a fixed chemical crosslink density but at various initial monomer concentrations. The gels were characterized by swelling and elasticity tests as well as by light scattering measurements. PAAc gels exhibit a maximum degree of spatial inhomogeneity at a critical monomer concentration . shifts toward higher concentrations as the gel swells beyond its dilution degree after preparation. Depending on the polymer concentration in gels, swelling reduces or enhances the extent of the spatial inhomogeneities. It was shown that the apparent degree of the spatial gel inhomogeneity is determined by the combination of three effects, namely the effects of the effective crosslink density, charge density and segment density. The relative magnitudes of these effects vary depending on the polymer concentration and lead to the appearance of a maximum degree of spatial inhomogeneity at a critical concentration.