Adiabatic compressibility of polyelectrolytes: Effect of solvents on copolymers of vinyl pyrrolidone with acrylic acid and N-dimethylaminoethyl methacrylate

The results of adiabatic compressibility measurements for two copolymers, acrylic acid-vinyl pyrrolidone (AA—VP) and N-dimethylaminoethyl methacrylate-vinyl pyrrolidone (DAM—VP), in three different solvents, namely, water, methanol, and dioxane, have been described. The molecular weight of copolymers was determined by the light scattering method and the IR and NMR spectra of the polymers and copolymers were examined to establish that the alternating acrylic acid–vinyl pyrrolidone and N-dimethylaminoethyl methacrylate–vinyl pyrrolidone structure exists in the copolymers. The AA—VP copolymer behaves as a slightly weaker acid than the homopolymer of acrylic acid, while DAM—VP copolymer is very feebly basic and has the same strength as that of the homopolymer of N-dimethylaminoethyl methacrylate. The reduced viscosity for the two copolymers in aqueous solution is very low (～0.08 dL/g for AA—VP copolymer). In methanol solution AA—VP and DAM—VP copolymers show a decrease of øK^°₂ and øV^°₂ by 61.6 × 10^?4 cc/bar/mol and 8.0 cc/mol, and 191.0 × 10^?4 cc/bar/mol and 20.0 cc/mol, respectively, over that of the values of aqueous solution. The void space around the solute is smaller in methanol than in water, and accordingly this decrease has been attributed to geometric effect. Only one copolymer, DAM—VP is soluble in dioxane, and the values are seen to have increased in this solution by 71.0 × 10^?4 cc/bar/mol and 18.7 cc/mol, respectively, compared to the values obtained from aqueous solution. The experimentally determined øK^°₂ and øV^°₂ for AA—VP and DAM—VP copolymer are 0.6 × 10^?4 cc/bar/mol, and 102.4 cc/mol and ?61.0 × 10^?4 cc/bar/mol, 94.4 cc/mol, respectively, in aqueous solution, and ?12.0 × 10^?4 cc/bar/mol, 211.0 cc/mol and ?203.0 × 10^?4 cc/bar/mol, 191.0 cc/mol, respectively, in methanol solution. In dioxane solution the values for DAM—VP copolymer are 59.0 × 10^?4 cc/bar/mol and 229.7 cc/mol, respectively. These experimentally determined values for AA—VP copolymer show an increase by 0.04 × 10^?4 cc/bar/mol, 4.4 cc/mol and 28.3 × 10^?4 cc/bar/mol, 8.0 cc/mol in aqueous and methanol solution, respectively, compared to calculated values determined on the basis of no interaction between acid and the pyrrolidone group. In contrast, the DAM—VP copolymer shows a decrease of 27.6 × 10^?4 cc/bar/mol and 10.3 cc/mol, 149.3 × 10^?4 cc/bar/mol and 20.2 cc/mol, and 23.0 × 10^?4 cc/bar/mol and 4.1 cc/mol in aqueous, methanol, and dioxane solutions, respectively. In aqueous solution these differences between calculated and observed values have been attributed to a change of water structure around the copolymer chain. A similar effect is responsible for the difference of the values in the methanol solution also. In the dioxane solution the difference is rather small, and the solvent structure has probably not altered much due to the presence of the DAM unit in the chain.     

The adiabatic compressibility of polyelectrolytes: Sodium and hydrochloride salts of acrylic acid–N-dimethylaminoethyl methacrylate copolymer

The results of adiabatic compressibility measurement for the 100% neutralized sodium and hydrochloride salts of three copolymers of acrylic acid and N-dimethylaminoethyl methacrylate, namely, AA-DAM 58, AA-DAM 43, and AA-DAM 33, are discussed. Similar to three unneutralized amphoteric polyelectrolytes, the ?K₂ and ?V₂'s for these salts are found to be concentration independent. Since in the former both anionic and cationic groups are present, fully neutralized sodium salts and hydrochloride salts of these polyelectrolytes are expected to show a decrease in ?K_2i⁰ and ?V_2i⁰ values due to maximum electrostriction. In fact, in case of AA-DAM 58 with excess amino group in the chain (58%), the experimentally obtained values are found to be ?9.6 × 10^?4 cc/bar/mole and 159.6 cc/mole, and ?3.3 × 10^?4 cc/bar/mole and 164.4 cc/mole for sodium and hydrochloride salts, respectively, which corresponds to a decrease of 7.1 × 10^?4 cc/bar/mole and 4.9 cc/mole for the sodium salt and 0.8 × 10^?4 cc/bar/mole and 0.1 cc/mole for the hydrochloride salt. In contrast, the hydrochloride salt of AA-DAM 43 shows an increase of 6.2 × 10^?4 cc/bar/mole and 2.2 cc/mole, respectively, while in case of AA-DAM 33, both the hydrochloride salt (56.2 × 10^?4 cc/bar/mole and 24.7 cc/mole) and the sodium salt (6.2 × 10^?4 cc/bar/mole and 6.2 cc/mole) show an increase. This increase has been ascribed to suppression of dissociation of carboxyl groups by the hydrochloric acid (common ion effect) added for neutralization. However, in all the three amphoteric copolymers, when neutralized with NaOH solution or HCI acid, the viscosity increases over that of the unneutralized copolymer.     

Adiabatic compressibility of polyelectrolytes in aqueous solutions: Poly(methacrylic acid)

The adiabatic compressibility of dilute aqueous solutions of methacrylic acid, poly-(methacrylic acid), and three poly(sodium methacrylates) obtained by neutralizing the polyacid with sodium hydroxide to different extents were determined from soundvelocity and density data. The ultrasonic velocity at 25°C. was measured by employing a precision ultrasonic interferometer, and the density was measured with Ostwald-type pycnometers. The plots of the decrease of compressibility per unit concentration, (β₁ ? β)/c versus c shows that there is a marked difference between the curves of monomer and of polymer solutions. In case of the monomer there is a proportional decrease with increase in concentration, whereas in polymer in the dilute region (0.1?0.5g./dl.) the curve rises sharply, then shows down, and finally approaches a constant value at comparatively higher concentrations. The nature and number of the free counterions and the shape and the concentration of the polymer molecules are responsible for the compressibility of polymer solutions. However, the contribution of the size and shape and concentration of the polymer seem to be less than that of the nature and number of the counterions. The apparent molal volume ΦV₂ and apparent molal compressibility ΦK₂ for polymer repeat units show a sharp decrease with increase in concentration and finally attain a constant value at higher concentrations; this has been explained by the fact that in the dilute region the polymer, being extended by coulombic repulsion between similar charges situated on the side chain, enhances the formation of water clusters around it, and the free counterions are solvated, leading to a decrease to these values. The number of free counterions proportionately increases with concentration, causing a proportional decrease of the ΦV₂ and ΦK₂ values, until the concentration reaches a definite stage, above which the so-called condensation of ions occurs, and the number of free counterions does not increase further at higher concentrations.     

Adiabatic compressibility of some amphoteric polyelectrolytes

The results of adiabatic compressibility measurements for two amphoteric polyelectrolytes, acrylic acid–4-vinyl-N-n-butylpyridinium bromide copolymer and methacrylic acid–4-vinyl-N-n-butylpyridinium bromide copolymer, and their completely neutralized potassium salts have been described. The two amphoteric polyelectrolytes are strongly acidic, and the strength of the acidic group has been increased by the presence of the neighboring basic group. The reduced viscosity for these polyampholytes is extremely low (～0.03–0.07 dl/g) which may be on account of the mutual interaction of acid and base groups making the polyelectrolyte chain highly coiled and compact. The apparent molal volume ΦV₂ and apparent molal compressibility ΦK₂ are concentration independent. Their potassium salts showed the lowest ΦV₂ and ΦK₂ values as the electrostriction is highest here; these values showed a slight increase in the presence of dilute KBr solution as the dissociation is somewhat reduced. However, in excess KBr solution, the acrylic acid-containing copolymer having comparatively more carboxyl groups (21.7%) behaves more or less similar to poly(acrylic acid), whereas the methacrylic acid-containing copolymer, with only 15.1% carboxyl groups, behaves closely to poly(4-vinyl-N-n-butylpyridinium bromide). These polyelectrolytes showed absorption in the 2700 to 3800 Å region in the presence of chloride, bromide, and iodide ions which are due to charge transfer complex formation between the halide ions and the polymer nucleus. The magnitude of extinction coefficient for these two polyampholytes is much less than that of poly(4-vinyl-N-n-butylpyridinium bromide). The limiting values of apparent molal volume, ΦV₂⁰, for acrylic acid- and methacrylic acid-containing copolymers are 183.9 and 184.6 cc/mole, respectively. These experimentally determined values fall short of 9.2 and 6.2 cc/mole compared to the calculated values (if there was no interaction between acid and base groups) which are definitely due to mutual interaction of acid and base groups in the polymer chain.     

Adiabatic compressibility of polyelectrolytes: The influence of solvents on ionic and nonionic polymers

The adiabatic compressibility of two ionic polymers; namely, poly(acrylic acid) (PAA) and poly(N-dimethylaminoethyl methacrylate) (PDAM) in methanol and dioxane solutions and of a nonionic polymer, poly(vinyl pyrrolidone) (PVP) in aqueous, methanol, and dioxane solutions has been studied. The φV₂ and φK₂ values for the three polymers and their corresponding monomers in methanol and dioxane solutions are found to be concentration independent. There is a marked difference in φK⁰₂ and φV⁰₂ values between monomer and polymer in all three solvents. In aqueous solution, the difference in φV⁰₂ is, on an average, 16.1 cm³/mol, while in methanol and dioxane solution, the same is 24.0 and 20.5 cm³/mol (average), respectively. All three monomers in dilute aqueous solution show a contraction of volume and decrease of adiabatic compressibility which are comparatively small in methanol and dioxane solutions. The φV⁰₂ for PAA, PDAM, and PVP were found to have increased by 0.8, 11.0, and 1.5 cm³/mol, respectively, in dioxane solution over that of the value of the aqueous solution. It is interesting to note that in methanol solution, PAA, PDAM, and PVP show a decrease of φK⁰₂ and φV⁰₂ values by 68.8 cm³/bar/mol and 8.2 cm³/bar/mol, 32.7 cm³/bar/mol, and 4.3 cm³/mol, and 36.6 cm³/bar/mol and 5.8 cm³/mol, respectively, compared to the values obtained from aqueous solution. This has been ascribed to geometric effect since the void space around the molecules is smaller in methanol than in water.     

Poly(butadiene-acrylic acid(g)acrylonitrile(g)acrylic acid)

Summary In the present work we describe, the synthesis and characterization of a new gel obtained by crosslinking a cooligomer of butadiene-acrylic acid (BuAA), by reaction with acrylonitrile and acrylic acid. The purified product was characterized by FTIR, elemental analyses and scanning electronic microscopy. The thermal properties were studied and swelling indexes were determined in different solvents and at different pH values. The capacity of poly(butadiene-acrylic acid(g)acrylonitrile(g)acrylic acid) [gel A] to separate different organic substances, such as amino acids and colorants, was determined.     

Poly(acrylic acid)-grafted magnetic nanoparticle for conjugation with folic acid

Poly(acrylic acid) (poly(AA))-grafted magnetite nanoparticles (MNPs) prepared via surface-initiated atom transfer radical polymerization (ATRP) of t-butyl acrylate, followed by acid-catalyzed deprotection of t-butyl groups, is herein presented. In addition to serve as both steric and electrostatic stabilizers, poly(AA) grafted on MNP surface also served as a platform for conjugating folic acid, a cancer cell targeting agent. Fourier transform infrared spectroscopy (FTIR) was used to monitor the reaction progress in each step of the syntheses. The particle size was 8 nm in diameter without significant aggregation during the preparation process. Photocorrelation spectroscopy (PCS) indicated that, as increasing pH of the dispersions, their hydrodynamic diameter was decreased and negatively charge surface was obtained. According to thermogravimetric analysis (TGA), up to 14 wt% of folic acid (about 400 molecules of folic acid per particle) was bound to the surface-modified MNPs. This novel nanocomplex is hypothetically viable to efficiently graft other affinity molecules on their surfaces and thus might be suitable for use as an efficient drug delivery vehicle particularly for cancer treatment.     

Poly(N,N-dimethylaminoethyl methacrylate)/graphene oxide hybrid hydrogels: pH and temperature sensitivities and Cr(VI) adsorption

Different amounts of graphene oxide (GO) were incorporated to N,N-dimethylaminoethyl methacrylate (DMAEMA), fabricating a series of pH and temperature dual sensitive PDMAEMA/GO hybrid hydrogels by in situ polymerization. Their microscopic network structures as well as swelling properties and Cr(VI) adsorption were characterized. The equilibrium swelling ratios (ESR) of hydrogels increased significantly with 0.5 wt% GO feeding of DMAEMA amount, and then decreased with further GO loading increasing. All hydrogels showed obvious deswelling when pH value of swelling mediums increased from 5 to 10 gradually. At pH 7, hydrogels revealed slight ESR increment with temperature up to 50 °C, above which obvious deswelling occurred. In pH 8 buffer, 0.5 wt% of GO loading triggered lower critical solution temperature (LCST) to decrease by 3 °C, and 2–7 °C increment was observed when 1–6 wt% of GO was loaded, as compared with that of GO-free PDMAEMA hydrogel. Cr(VI) adsorption of hydrogels was also improved by the introduction of GO to some extent, and the maximum Cr(VI) adsorption of 180 mg/g was realized, indicating that the obtained PDMAEMA/GO hybrid hydrogels possess excellent adsorption performance.     

Hot Melt Reactive Extrusion of Chitosan with Poly(acrylic acid)

The hot melt reactive extrusion of blends of chitosan and poly(acrylic acid) (PAA) was carried out without any process additives such as organic solvent or plasticizer. The maximum amount of chitosan in the blend during the extrusion process was kept at 40 wt%, since the melt viscosity of a system containing 50 wt% of chitosan exceeded the torque limitation of the equipment. The carboxylic groups of PAA interacted with the amine groups of chitosan during the melt process, and the system exhibited good melt flow. The interactions between these two polymers were explained by investigating the results obtained by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC). The thermal transition behavior of PAA was altered with a decrease of more than 10°C in the peak melting point after extrusion. The infrared (IR) spectroscopic data confirmed the existence of a complex formation and possible hydrogen bonding between chitosan and PAA during the melt process. Scanning electron microscopy (SEM) micrographs indicated that chitosan was well-dispersed in the PAA blends up to 30 wt% chitosan, with no indication of loose particles or other disruptions on the upper and lower fractured faces. This smooth interface might have been caused by the interaction between amide bonds of chitosan and carboxylic groups of PAA.     

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.     

Cross-Linked Poly(acrylic acid) Microgels from Precipitation Polymerization

Cross-linked poly(acrylic acid) microgels were prepared via thermally initiated free-radical precipitation polymerization in a binary organic solvent. N,N′-Methylenebisacrylamide (MBA) and 2,2′-azobisisobutyronitrile were used as cross-linker and initiator, respectively. The effect of (MAB) concentration on different features of sample (i.e., spectral characteristics, glass transition temperature, equilibrium swelling, gel content and rheological properties) was investigated. The Flory-Rehner equation and rubber elasticity theory were used to discuss the network structure of polymer. Apparent and rotational viscosities were used to determine the optimal cross-linker concentration. The sample maximum with value of viscosity was obtained using 1.6 mmol/L of the cross-linker. In addition the m and n parameter of Ostwald equation were investigated as well.     

Poly(acrylic acid)-guided synthesis of helical polyaniline microwires

We present a facile method to prepare helical polyaniline (PANI) microwires or rods guided by poly(acrylic acid) (PAA). The average length and diameter of the helical strands were about 3.5 μm and 500 nm, respectively. The pitch distance was about 400 nm. The morphology of the helical PANI microwires was affected by the concentration of PAA. As the concentration was decreased to below 0.05 mg/ml, helical wire- or rod-like products were observed. The structure of the helical polyaniline microwires were characterized by means of TEM, SEM, XRD, FTIR and UV-vis spectroscopy.     

Synthesis of N,N'-diallylmalonamide and its copolymer gels with acrylic acid and acrylamide

N,N'-diallylmalonamide (DAM) has been prepared via classical aminolysis of diethyl malonate with allylamine. Its structure was confirmed by elementary microanalysis as well as ¹H NMR and FT-IR spectroscopy. The new diallyl monomer is water-soluble and able to copolymerize radically with water-soluble monomers, such as acrylamide and acrylic acid, to give transparent hydrogels by using K₂S₂O₈ as initiator. Homopolymerization of DAM yields clear hydrogels with high swelling ability.     

Colloidal Processing of Silicon Nitride with Poly(acrylic acid): II, Rheological Properties

Poly(acrylic acid) (PAA) was the focus of an investigation in the role and behavior of polyelectrolyte dispersants in aqueous-based colloidal processing of silicon nitride. The steady-shear flow properties of dense suspensions were examined as a function of pH, particle volume fraction, chain length, and polymer concentration. Suspensions exhibited shear-thinning behavior, which was analyzed using the constitutive Bingham equation for plastic flow. The data showed that polyelectrolyte charge and configuration were important in the observed flow behavior. In acidic media, PAA behaved similar to a neutral polymer in a poor solvent, whereas, in alkaline media, PAA behaved similar to a rigid asymmetric particle. Although electrostatic forces dominated flow properties in alkaline media, where PAA was predominantly in the free-polymer form, at lower pH values, PAA interactions with the particle surface resulted in a complex array of suspension effects, including polymer bridging, electrosteric stabilization, and flocculation.     

Synthesis of poly(acrylic acid)-g-polystyrene copolymer by successive ATRP

A series of well-defined amphiphilic graft copolymers consisting of hydrophilic poly(acrylic acid) backbone and hydrophobic polystyrene side chains were synthesized by hydrolysis of poly(methyl acrylate)-g-polystyrene under basic condition. The backbone and the side chains were synthesized by atom transfer radical polymerization (ATRP), so the molecular weight could be tuned by the variation of the feed ratio or monomer conversion, and the molecular weight distributions of amphiphilic graft copolymers were kept low (PDI < 1.35). The products were characterized by FT-IR, ¹H NMR, ¹³C NMR, and gel permeation chromatography (GPC). The study of self-assembly behavior can benefit the formation of the well-defined structures of the products.     

聚甲基丙烯酸/SBA-15复合物的制备

采用超声波分散技术,通过原位合成法将pH敏感的功能单体甲基丙烯酸(MAA)引入到介孔二氧化硅SBA-15的孔道内聚合,制备了pH敏感SBA-15/聚甲基丙烯酸(PMAA)纳米复合材料,对材料的结构和性能进行了测试。结果表明,介孔分子筛SBA-15/PMAA复合材料有较好的光学性能、热性能。聚合反应的发生并没有破坏SBA-15的有序介孔结构,显示出pH敏感性,有望在药物缓释领域得到应用。     

Poly(N-isopropylacrylamide-acrylic acid) copolymer microgels for various applications: A review

Smart polymer microgels have been attracting a lot of attention due to their quick response to variation in environmental stimuli like temperature, pH, ionic strength, and presence of some biological molecules. Poly(N-isopropylacrylamide) and its copolymer microgels have been synthesized and characterized for various applications in last 10 years. Synthesis, properties, and applications of poly(N-isopropylacryamide-co-acrylic acid) [P(NIPAM-AA)] copolymer microgels have been extensively reported in literature. This article describes synthesis, fundamental properties, and applications of P(NIPAM-AA) microgels in the field of medical science, environment, nanotechnology, catalysis, and photonics.     

壳聚糖/聚丙烯酸共聚物微球的制备及性能

以环己烷为油相,壳聚糖溶液为水相,运用反相乳液聚合法制得了具有pH敏感性的壳聚糖/聚丙烯酸共聚物微球。讨论了微球在pH=1～10缓冲溶液中的溶胀率变化,研究表明,微球在强酸性(pH≈1)和碱性(pH>7)条件下,溶胀率均在10倍以上;而在pH=2～6时溶胀较差,当pH=4时出现最低值,溶胀率低于1倍。光学显微镜所观察到的微球粒径均在40μm以内,且大小均匀。采用傅里叶红外光谱仪分析了不同配比样品特征峰的峰值和峰面积的变化。用722光栅分光光度计研究了共聚物微球包埋考马斯亮蓝的溶胀释放过程。     

Colloidal Processing of Silicon Nitride with Poly(acrylic acid): I, Adsorption and Electrostatic Interactions

The role of poly(acrylic acid) (PAA) in the dispersion of silicon nitride suspensions was investigated experimentally. The effects of concentration, relative molecular mass, and suspension pH were evaluated. The ionization of PAA was characterized by potentiometric titration and indicated a pH-dependent conformational transition. The isoelectric point for silicon nitride decreased from pH 6.3 to pH 3 as the PAA concentration increased, roughly independent of relative molecular mass. A broadening of the stability region for silicon nitride was attributed to this effect. Redispersion in alkaline media, subsequent to destabilization by surface-charge neutralization, improved following preadsorption of PAA in acidic media. This effect was attributed to formation of a protective polymer adlayer on the surface, which prevented primary minimum aggregation; an electrosteric contribution also may be present. The influence of free polymer on the suspension properties also is discussed.     

Poly(acrylic acid)–poly(vinyl alcohol) copolymers with superabsorbent properties

Biodegradable polyacrylates were produced by a series of novel copolymerization and/or crosslinking techniques using poly(vinyl alcohol) (PVA) moieties modified by the incorporation of olefinic structures. PVA was modified by a tosylation and/or detosylation reaction. The functionalized PVA was copolymerized and/or crosslinked with acrylic acid or its partially neutralized form to give crosslinked polyacrylates that could swell in water. Their swelling behavior was determined under load. Degradation studies were performed in α-chymotrypsin, trypsin, and papain solutions. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 70: 817–829, 1998