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.     

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.     

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.     

聚乙烯醇/聚丙烯酸/腐植酸钠高吸水性树脂的制备及溶胀行为

以N,N＇-亚甲基双丙烯酰胺为交联剂、过硫酸铵为引发剂,采用水溶液聚合法合成了聚乙烯醇/聚丙烯酸/腐植酸钠多功能高吸水性树脂。研究了聚乙烯醇和腐植酸钠含量对树脂吸水倍率的影响,同时考察了树脂的吸水速率、溶液pH值对吸水倍率的影响及反复溶胀性能。结果表明,在体系中引入廉价的腐植酸钠,能够显著提高树脂的吸水能力。在腐植酸钠含量为10wt%时,树脂具有最高的吸水倍率,其吸蒸馏水和0.9wt%NaCl溶液分别达到1020g/g和80g/g。     

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.     

Ionically crosslinked poly(acrylic acid) membranes. I. Wet technique

A study has been made of the ionic crosslinking of poly(acrylic acid) membranes for possible applications in dialysis and reverse osmosis. The technique consists of casting a film of poly(acrylic acid) neutralized with sodium hydroxide, followed by immersion in appropriate metal salts (aluminium, zinc, and chromium salts). A qualitative rate model has been developed to guide this synthesis. Since both metal cations and protons in solution compete for the carboxylic acid sites, acid–base properties of the metal and polycarboxylic acid appear to be important for successful membrane formation. The use of a nonsolvent for the polymer in the crosslinking solution was tested and found to give improved membranes under some conditions. The nonsolvents tested were methanol, acetone, benzene, and dimethylformamide, dimethylformamide being the most successful. Crosslinking agents such as the Zn²⁺ and Cr³⁺ salts were tried but were not as successful as the Al³⁺ salts. A series of membranes was synthesized in aluminium/dimethylformamide crosslinking baths under various conditions in order to determine suitable procedures for preparation of membranes.     

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 %.     

Diffusion phenomena of small molecules in polyelectrolyte solutions

Summary From diffusion data of xylose in poly (acrylic acid) and in poly(sodium acrylate) aqueous solutions, the behaviour of these polymers in solution is discussed. When these polyelectrolytes are ionized and expanded in water, consequently, the diffusion phenomena of xylose in these solutions follows the theory of linear macromolecules in solution. When NaCl is added in poly (acrylic acid) solution, the polymer chain contracts and becomes spherical. Therefore, xylose cannot pass through the polymer domain. With poly(sodium acrylate), however, an effect of salt has not been found. Furthermore, effects of neutralization are discussed.     

Phase behaviour of methylcellulose–poly(acrylic acid) blends and preparation of related hydrophilic films

The phase behavior of methylcellulose‐poly(acrylic acid) mixtures was studied in aqueous solution. It was shown that the complexation between the two polymers decreases considerably the cloud‐point of methylcellulose. The addition of inorganic salts shifts the critical pH values toward a higher pH region. Films were prepared based on methylcellulose‐poly(acrylic acid) blends and were analyzed by dynamic mechanical thermal analysis, scanning electron microscopy and thermal gravimetric analysis. The miscibility between the two polymers in the films was shown. It was found that the thermal treatment of the films leads to their cross‐linking with the formation of materials swellable both in water and ethanol. © 2003 Society of Chemical Industry     

The adiabatic compressibility of poly(acrylic acid) and polyacrylamide in aqueous solution

The results of adiabatic compressibility measurements of poly(acrylic acid) and polyacrylamide along with their corresponding monomers and two poly(sodium acrylates) obtained by neutralizing the polyacid 25% and 100% with sodium hydroxide have been described. The total adiabatic compressibility of poly(acrylic acid) solution is higher than that of the corresponding salt solutions or of polyacrylamide solutions. The unneutralized acid does not dissociate much, even in dilute solution, and the magnitude of electrostriction in polyamide is greater than in acid. The ΦV₂ and ΦK₂ values for monomers and polymers are seen to be almost concentration independent, and so are the sodium salts of the polyacid. Poly(acrylic acid) and poly(acrylamide) are structurally closely related polymers, and water must be bound to them through polar groups either by hydrogen bonding or by dipole attraction. The hydrophobic part of the solute, because of compact orientation of water and solute in the boundary region, causes a decrease in solvent volume and therefore in the values of ΦV₂ and ΦK₂. On the other hand, intermolecular hydrogen bonding between the polar groups increases the volume and counterbalances the hydrophobic effect. Because of these two counteracting effects, the observed ΦV₂ and ΦK₂ values are seen to be concentration independent. Contrary to the observation with poly(methacrylic acid)¹ and its sodium salts, the solvated counter-ions in case of poly(sodium acrylates) make no special contribution in the dilute region. In 100% neutralized polyacid, the dissociation of counterions is complete, and the magnitude of electrostriction is highest in this case. Accordingly, lowest ΦV₂ and ΦK₂ values (37.0 cc/mole and ?50.50 × 10^?3 cc bar^?1 mole^?1) are observed. However, the dissociation and therefore the magnitude of electrostriction are somewhat reduced in the presence of 1.0M NaCl solution; and, accordingly, the values increase to 42.80 cc/mole and ?33.0 × 10^?4 cc bar^?1, mole^?1, respectively. The limiting values for the apparent molal volume and the apparent molal compressibility for the polymers show a considerable decrease over those of the monomers. The values of ΦV₂⁰ and ΦK₂⁰ per methyl group are less in the polymers than in the monomers, and this has been attributed to water clusters that become stronger and better formed as the molecules grow larger and larger. The molar volumes of acrylic acid and methacrylic acid are decreased, while those of acrylamide and methacrylamide are increased when dissolved in water to form an infinitely dilute solution.     

Influence of the COOH and COONa groups and crosslink density of poly(acrylic acid)/montmorillonite superabsorbent composite on water absorbency

A novel poly(acrylic acid)/montmorillonite superabsorbent composite with a water absorbency of 1100 times its own weight was synthesized by the graft copolymerization of acrylic acid with a cross‐linking agent in the presence of montmorillonite ultrafine powder. The influence of the amount of crosslinker and montmorillonite on water absorbency has been investigated. It was found that a crosslinker concentration of 0.03 wt% and 30 wt% montmorillonite gave the best results. The collaborative absorbent effect of sodium carboxylate and carboxylic acid groups was superior to that of sodium carboxylate or carboxylic acid groups alone, and the composite with a ratio of about 2/3 for sodium carboxylate to carboxyl acid groups possessed the highest water absorbence. © 2001 Society of Chemical Industry     

Effects of poly(acrylic acid) and poly(ethylene oxide) adsorption on the stability of alumina suspension

The effect of adsorbed polymer on the stability of alumina suspension was investigated. Poly(ethylene oxide) (PEO), poly(acrylic acid) (PAA) and similar kinds of polymer salts were used as a dispersant. The amount of polymer adsorbed on alumina surface and the suspension stability was measured. The pH, molecular weight, and concentration were considered as experimental parameters. PEO shows low affinity on the alumina surface while PAA has high affinity. In the case of PAA adsorption, the surface charge change by polymer adsorption influences suspension stability strongly, but not in the case of PEO adsorption. In simultaneous adsorption of PEO and PAA, the PAA concentration was fixed and PEO concentration was varied. The stability of suspension increased with increasing PEO concentration, and this is partly due to the steric stabilization by adsorption of PAA-PEO complex or adsorption of PEO through pre-adsorbed PAA and the depletion effect of non-adsorbed polymer. Suspension adsorbing sodium salts of PAA and poly(methacrylic acid) (PMA) each showed similar stability. But, when the PEO and these kinds of salts were added together to the suspension, the one with PAA sodium salt could keep a higher stability even with lower molecular weights of PEO compared with suspension with PMA sodium salt.     

Effect of drying conditions on the glass transition of poly(acrylic acid)

Systematic changes of drying conditions of poly(acrylic acid) were tested to study their effect on the glass transition of the material. The materials were synthesized in two different mediums of water and benzene, respectively. The glass transition temperatures of the samples were determined by thermal analysis using DSC. The samples were also characterized by IR spectra. The glass transition of poly(acrylic acid) was found to be significantly dependent on the drying conditions and also dependent on the medium in which poly(acrylic acid) was prepared. The anhydride formation in poly(acrylic acid) was increased as the drying temperature was raised, resulting in the increase of the glass transition temperature. The “bound” water involved in the preparation of poly(acrylic acid) in water medium could affect significantly the glass transition of the sample. A significant discrepancy in the previously reported values of the glass transition temperature of poly(acrylic acid) seems to be due to the differences in the drying conditions of the materials.     

Cerium–initiated Polymerisation of Some Vinyl Compounds in Polyamide Fibres

Several vinyl polymers have been grafted onto nylon 6. 6 with ceric salts as initiators. Some factors influencing the polymerisation of acrylic acid have been examined in detail, and evidence obtained that the products are true graft copolymers. Grafting of both 2–vinylpyridine and 4–vinylpyridine is slow from solutions in dilute sulphuric acid or nitric acid, but rapid from perchloric acid. Slow diffusion of initiator into polyamide fibres is apparently responsible for a non–uniform distribution of polymer sometimes observed. Nylon 6. 6 is oxidised slowly, but extensively, by cerie salts and the reaction is accelerated by oxygen. Analyses of the products are consistent with oxidation at methylene groups adjacent to the amide nitrogen rather than at amine end–groups. A paradox, thatdinitrophenylation renders nylon less susceptible to grafting of poly(acrylic acid), but not to oxidation by eerie salts, is tentatively explained. The surface electrical resistivity of nylon fabric is not lowered by grafted polyacrylamide or its N–alkyl derivatives, whilst salts of poly(acrylic acid) and poly(vinylpyridines) impart only a temporary lowering. Poly(1–rnethyl–4–vinylpyridinium) perchlorate was more permanently effective. Attempts to polymerise some potentially antistatic betaine–type monomers in nylon were unsuccessful.     

Über die Darstellung und Sulfatierung von N-substituierten 12-Hydroxyoctadecen-(9)-säure-(1)-amiden

Preparation and Sulfation of N-Substituted 12-Hydroxy-octadecan-(9) Acid-(1) Amides Ricinoleic acid amides, substituted at the nitrogen atom, were converted to the sodium salts of the monosulfuric acid esters of the substituted ricinoleic acid amides (sodium salt of substituted 12-hydroxy sulfonyl-oxy-oleic acid amide) by sulfation with chlorosulfuric acid-diethyl ester-adduct followed by neutralisation. Washing capacity as well as surface tension, angle of contact and wetting capacity in relation to the concentration of the aqueous solutions of these anion active surfactants are measured.     

腐殖酸-聚丙烯酸表面交联吸水性树脂的合成与性能

将交联剂N,N′-亚甲基双丙烯酰胺溶于甲醇溶液制成表面处理液,通过表面交联反应将磺化腐殖酸（HA）与聚丙烯酸(PAA)结合,制得一种适合于农林领域应用的腐殖酸-聚丙烯酸高吸水性树脂（HA-PAA）.研究了表面处理液浓度、交联剂用量和腐殖酸量对HA-PAA吸水性能的影响规律和吸水机理,以及产物在沙土中的保水性能,并通过扫描电镜分析了HA-PAA的表面结构.研究结果表明,当含有10% HA时,HA-PAA耐电解质性能良好,吸水性能最佳;当沙土中添加0.2%的HA-PAA时,可明显改善沙土的贮水、保水性能.HA-PAA作为农林领域用保水剂,可发挥抗旱保墒和促进植物生长的双重作用.     

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.     

Dialysis membranes from polyethylene films grafted with acrylic acid

Low‐density polyethylene‐g‐poly(acrylic acid) membranes were prepared by the direct radiation grafting of aqueous acrylic acid solutions (containing Mohr's salt) onto low‐density polyethylene films and were irradiated at two different irradiation doses (2 and 3 Mrad) at a dose rate of 0.02 Mrad/h. Two series of polyethylene‐g‐poly(acrylic acid) membranes with 100 and 150% grafting were obtained. The free carboxylic acid groups in the grafted films were converted into the corresponding acrylates by reactions with different metal salts. The swelling (water uptake) and dialysis permeability of glucose and urea through the grafted membranes in different metal‐ion forms were investigated. The prepared membranes showed good permeability to both solutes, which increased as the hydrophilicity of the membrane increased. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 91: 10–14, 2004     

聚丙烯酸钠/高岭土复合高吸水性树脂的制备、结构与性能

以丙烯酸和高岭土为原料,用反相悬浮聚合法合成了聚丙烯酸钠/高岭土复合高吸水性树脂。研究了加入高岭土的聚丙烯酸钠复合高吸水性树脂合成中反应温度、中和度、交联剂用量、引发剂用量、高岭土添加量等影响树脂吸水性能的主要因素。结果表明,用反相悬浮聚合法合成的复合高吸水性树脂后处理容易,树脂的吸水率达到512g/g,吸盐水率达到81g/g,吸水速度比不加高岭土提高20%,保水能力提高15%,在250℃加热30min仍能保持原吸水率的95%。用IR和TEM研究了复合高吸水性树脂的表面和结构,TEM显示高岭土的加入对树脂颗粒大小和形状有较大的影响,IR初步表明聚丙烯酸与高岭土产生了交联。     

新型膦磺酸盐共聚物水处理剂的合成及性能研究

以水为溶剂，次亚磷酸钠-过硫酸钠为引发剂，丙烯酸（AA）和2-丙烯酰氨基-2-甲基丙磺酸（AMPS）为单体合成了集膦酸基、羧酸基和磺酸基于一体的共聚物。考察了该共聚物阻垢性能与单体配比、引发剂用量、反应温度和反应时间等之间的关系。研究结果表明，该共聚物具有较好的阻CaCO3垢、阻Ca3（PO4）2垢和抑制锌盐沉积的能力。