Showing papers on "Acrylic acid published in 1997"

Infrared, Raman, and Near-Infrared Spectroscopic Evidence for the Coexistence of Various Hydrogen-Bond Forms in Poly(acrylic acid)

Abstract: Fourier-transform infrared (FT-IR), near-infrared (NIR)-excited FT-Raman, and FT-NIR spectra have been measured for poly(acrylic acid) (PAA) in a cast film over a temperature range of 40−140 °C, to investigate structures of hydrogen bonds and their dissociation. The CO stretching bands in the FT-IR spectra are unraveled by a prevalent multiple species model for small aliphatic acids with various kinds of associated forms of carboxylic acid groups, namely cyclic dimer, linearly associated oligomers of COOH, and free COOH groups. These different structures of hydrogen bond persist even when the temperature rises well above the glass transition temperature. The FT-Raman spectra confirm the existence of such COOH groups. Temperature-dependent intensity changes in the first overtone of an OH stretching mode of PAA reveal that the COOH groups dissociate significantly at high temperatures. We propose that the coexistence of various possible hydrogen-bond forms analogous to those in small aliphatic acids best int...

A new approach for the fabrication of an alternating multilayer film of poly(4-vinylpyridine) and poly(acrylic acid) based on hydrogen bonding

Abstract: A new approach for the fabrication of a multilayer film assembly is explored, which is based on the alternating assembling of poly(4-vinylpyridine) and poly(acrylic acid) via hydrogen bonding. The homogeneous multilayer films were characterized by UV-Vis, X-ray diffraction and atomic force microscopy (AFM) measurements. The nature of interaction between the two polymers is identified as hydrogen bonding by IR spectroscopy.

pH-Responsive Gels of Hydrophobically Modified Poly(acrylic acid)

Abstract: pH-responsive gels of hydrophobically modified (HM) weak polyacid were prepared from acrylic acid and n-alkyl acrylates (n = 8, 12, 18). The HM gels obtained bear up to 20 mol % of n-alkyl acrylate units randomly distributed along the network chains. The pH-driven swelling of these gels upon ionization in an aqueous medium was studied. The effect of the fraction and of the side chain length of n-alkyl acrylate groups on the equilibrium degree of swelling was examined. It was shown that the swelling transition shifts to alkaline pH with increasing hydrophobicity of the gel. This was explained by the stabilization of the collapsed state of the gel by hydrophobic aggregation of n-alkyl side chains. The formation of such aggregates, which break down in the course of gel ionization, was confirmed by the fluorescent probe method with pyrene as a probe and by NMR spectroscopy. Potentiometric titration data of HM poly(acrylic acid) (PAA) gels and of the corresponding linear copolymers evidence that the introducti...

Phase Separation Behavior and Crew-Cut Micelle Formation of Polystyrene-b-poly(acrylic acid) Copolymers in Solutions

Abstract: Static light scattering was used to study the phase separation behavior of homopolystyrene and polystyrene-b-poly(acrylic acid) (PS-b-PAA) in DMF as a function of added water content. It was found that the critical water content (cwc), at which phase separation starts, depends on both the polymer concentration and the molecular weight. The higher the polymer concentration and the molecular weight, the lower the cwc. For PS homopolymer, phase separation involves the precipitation of the polymer chains. In the copolymer solution, phase separation results in the formation of regular crew-cut micelles consisting of a PS core and a PAA corona; thus, it is preferably referred to as microphase separation. The change of the micelle fraction as a function of water addition can be estimated from the relationship between the cwc and the initial copolymer concentration. The influence of added electrolytes, i.e., NaOH, HCl, NaCl, CaCl2, or Ca(Ac)2, on the self-assembly process of the copolymers in DMF was also explore...

Hydrogel-Coated Glassy Nanospheres: A Novel Method for the Synthesis of Shell Cross-Linked Knedels

Abstract: A novel method was developed to prepare shell-cross-linked knedel-like structures (SCK's), which are double-layered polymer nanospheres, in a convenient three-step procedure: (1) polystyrene-b-poly(acrylic acid) ((DPn)PS = 130, (DPn)PAA = 120) copolymer was prepared by sequential anionic polymerization of styrene and tert-butyl acrylate, followed by hydrolysis; (2) the amphiphilic block copolymer was allowed to self-assemble into spherical multimolecular micelles in a water and THF solvent mixture; (3) the poly(acrylic acid), comprising the shells of micelles, was cross-linked by amidation using several di- and multiamino linkers (2,2‘-(ethylenedioxy)bis(ethylamine), hexakis(ethylene glycol)diamine, hexamethylenediamine, and triethylenetetramine). The extent of cross-linking was controlled by the relative amount of cross-link reagent used. The SCK's were spherical, core−shell structures composed of polystyrene cores and cross-linked hydrogel-like shells. The sizes, shapes, and structural differences betw...

Generation and in Situ Evaluation of Libraries of Poly(acrylic acid) Presenting Sialosides as Side Chains as Polyvalent Inhibitors of Influenza-Mediated Hemagglutination

Abstract: This paper describes a simple, microscale method for generating and evaluating libraries of derivatives of poly(acrylic acid) (pAA) that present mixtures of side chains that influence their biologi...

Water-Soluble Nanospheres of Poly(2-cinnamoylethyl methacrylate)-block-poly(acrylic acid)

Abstract: Poly(2-cinnamoylethyl methacrylate)-block-poly(acrylic acid) (PCEMA-b-PAA), with PCEMA photo-cross-linkable and PAA water soluble, were synthesized and characterized. The polymer formed spherical micelles in DMF/water with PCEMA as the core and PAA as the corona. The photo-cross-linking of the micelles yielded water-soluble nanospheres. The nanospheres were characterized by transmission electron microscopy (TEM) and light scattering. Dynamic light-scattering studies revealed that the nanospheres could readily take up organics in water. Coagulation of the nanospheres could be induced by the addition of divalent cations. These properties may allow the use of the nanospheres as the traps for organics in contaminated waters.

Studies on chitosan and poly(acrylic acid) interpolymer complex. I. Preparation, structure, pH-sensitivity, and salt sensitivity of complex-forming poly(acrylic acid): Chitosan semi-interpenetrating polymer network

Abstract: A novel semi-interpenetrating polymer network (semi-IPN) membrane composed of crosslinked chitosan(cr-CS) and poly(acrylic acid) (PAA) was prepared. Evidence from infrared spectra proved the formation of polyelectrolyte complex through electrostatic interaction between groups from CS and COO− groups from PAA. The semi-IPN membrane swelled at high pH and at low pH exhibited a typical pH-sensitivity. Its swelling degrees in different salt solutions with the same ionic valence and equal ionic strength were on similar levels. Under certain ionic strength (I = 1.5 mol/L), the degree of swelling increased with increased metal ionic valence. Furthermore, the elongation of the semi-IPN membrane could vary reversibly by immersion into CaCl2 solution and KCl solution alternately. Reasons for the chemomechanical behavior are discussed. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 65:1445–1450, 1997

Preparation of superabsorbent polymers by crosslinking acrylic acid and acrylamide copolymers

Abstract: High water-absorbent copolymers comprising acrylic acid (AA) and acrylamide (AM) were prepared in the presence of a crosslinking agent, monofunctional aldehyde, by a solution polymerization technique using a redox initiation system. Such copolymers have very high water absorbency and absorbing kinetics to the distilled water. The copolymer formed which absorbed about 900 g water/g dry copolymer was used to study the influence of sodium chloride on the absorption capacity at 24°C. The swelling of this copolymer was studied in alcohol/water mixtures of increasing alcohol content at 294, 304, and 314 K. The main transition for ethanol/water and methanol/water mixtures is a rapid decrease of the retention capacity of the copolymer at 50–60 vol % ethanol and 55–65 vol % methanol, respectively. Swelling in distilled water at different temperatures (T) and the effect of solvent composition were also studied. Among the variables examined were initiator concentration, polymerization temperature, and amount of AM in the copolymer. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 64: 1345–1353, 1997

Synthesis and Characterization of Surface-Grafted, Hyperbranched Polymer Films Containing Fluorescent, Hydrophobic, Ion-Binding, Biocompatible, and Electroactive Groups

Abstract: We report the derivatization of hyperbranched poly(acrylic acid) (PAA) films with a wide range of amino- or alcohol-terminated molecules. These molecules can include moieties such as pyrene, ferrocene, poly(ethylene glycol), 15-crown-5, and a dye. To derivatize PAA films, we activate their carboxylic acid groups with isobutyl chloroformate and allow them to react with amine- or alcohol-containing molecules. Infrared spectroscopy demonstrates the formation of amide and ester bonds upon coupling as well as the presence of the derivative functional groups. Excimer fluorescence from pyrene-containing films implies a high density of pyrene groups. However, we can control the amount of pyrene in the film (and obtain monomer fluorescence) by varying the concentration of Py(CH2)3CONH(CH2)2NH2 in the derivatization solution. Cyclic voltammetry of ferrocene-containing films shows an electrochemically addressable ferrocenyl surface coverage of (6 ± 3) × 10-9 mol/cm2 in three-layer PAA films. PAA films and their deri...

Temperature- and pH-sensitive terpolymers for modulated delivery of streptokinase

Abstract: Controlled release devices were designed which respond to changes in pH and temperature by reversibly swelling and deswelling to control release of streptokinase. Copolymer hydrogels composed of N-isopropylacrylamide (NIPAAm) and methacrylic acid (MAA) as well as terpolymer hydrogels containing NIPAAm, acrylic acid (AA), and 2-hydroxyethyl methacrylate (HEMA) were synthesized. Hydrogels containing NIPAAm display a change in swelling behavior across the lower critical solubility temperature of PNIPAAm, whereas hydrogels with MAA and AA swelled only at high pH values due to the ionization of carboxylic pendant groups. HEMA was chosen as a third component to add mechanical strength and integrity to the hydrogel. Pulsatile pH- and temperature-dependent swelling studies were performed to determine the extent and rate at which the hydrogels swell in response to changing conditions. Results showed that increasing the NIPAAm concentration in the copolymers or terpolymers resulted in a higher degree of temperature...

Acrylonitrile-modified toner compositions and processes

Abstract: A toner comprised of pigment, and an addition polymer resin generated from about 55 to about 80 weight percent of styrene, from about 1 to about 25 weight percent of acrylate, from about 1 to about 20 weight percent of acrylonitrile, and from about 0.5 to about 5 weight percent of acrylic acid.

Poly(acrylic acid)-cetyltrimethylammonium bromide interactions studied using dynamic and static light scattering and time-resolved fluorescence quenching

Abstract: Poly(acrylic acid) (PAA) and cetyltrimethylammonium bromide (C(16)TAB) are found to interact strongly in aqueous solution. The properties of the system are determined mainly by the parameter beta, defined as [C(16)TAB]/[PAA]; the PAA concentration is expr

New water-soluble photo crosslinkable polymers based on modified poly(vinyl alcohol)

Abstract: Poly(vinyl alcohol) (PVA) was partially modified by polymer analogous reaction with acrylic and methacrylic acid and with 2-vinyl-4,4-dimethyl-azlactone to obtain water-soluble polymers with pendant (meth)acrylate and acrylamide groups. Aqueous solutions of these polymers were crosslinked by UV-irradiation within seconds to form transparent networks with potential for use in contact lenses. The water content of these hydrogels was studied as a function of polymer molecular weight, the acetate, (meth)acrylate, and methacrylamide contents and irradiation conditions. The hydrogels showed good mechanical properties, even at low crosslinker (<5 mol %) and high water contents (60–80%). The formation kinetics and stability of aggregates, investigated by combined GPC/light-scattering measurements of samples annealed and/or stored at different temperatures (−20 to 100°C), give insight into PVA secondary structures. © 1997 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 35: 3603–3611, 1997

Acrylic acid polymerization kinetics

Abstract: The kinetics of the isothermal polymerization of acrylic acid were determined utilizing 1H-NMR spectroscopy. The polymerization rate was observed to depend approximately on the power of monomer and the power of sodium persulfate concentration. This is consistent with a model in which the rate of initiation is itself dependent on the monomer concentration. The polymerization rate was also observed to have a strong dependence on percent neutralization, decreasing with increasing level of neutralization up to 75 to 100% neutralization, and then increasing again. The activation energy for the rate of polymerization was between 9 and 13 kcal/mol except for 100% neutralized acrylic acid, which had an activation energy of 18 kcal/mol. These data suggest that a transition in mechanism occurred at 100% neutralization. Increasing the ionic strength by the addition of sodium chloride also increased the rate. The dependence of the molecular weight on the above variables was also quantified for use in the model. It decreased with increasing conversion, decreasing ionic strength and increasing initiator. © 1997 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 35: 2029–2047, 1997

Uv-absorbing polymer particle

Abstract: PROBLEM TO BE SOLVED: To enhance stability of a UV absorber. SOLUTION: The UV absorbing polymer particles are polymerization product of an unsaturated monomer of ethylene series selected from a group consisting of esters and amides of acrylic acid or methacrylic acid, vinyl esters, vinyl ethers and vinyl nitriles, an initiator, a surfactant and a UV absorber expressed by the formula (Rs are each independently H, a halogen, an alkyl, a 6-20C aryl, an alkoxy, an aryloxy, an alkylthio, an arylthio, an amine, an alkylamino, an arylamino, hydroxyl, cyano, nitro, an acylamino, sulfonyl, a sulfamide, an acyloxy and oxycarbonyl).

Indomethacin release behaviors from pH and thermoresponsive poly(vinyl alcohol) and poly(acrylic acid) IPN hydrogels for site‐specific drug delivery

Abstract: A temperature- and pH-responsive drug delivery system was studied by using interpenetrating polymer network (IPN) hydrogels constructed with poly(acrylic acid) (PAAc) and poly(vinyl alcohol) (PVA). The release of indomethacin incorporated into these hydrogels showed pulsatile patterns in response to both pH and temperature. Indomethacin diffused from the polymer matrices through the swelling and deswelling mechanism. The release amount increased at higher temperature because of the swelling caused by the dissociation of hydrogen bonding. The drastic change of drug release was achieved by alternating pH of the buffer solution and was attributed to the change of states of ionic groups within IPN hydrogels. The free water contents were calculated by using differential scanning calorimetry (DSC), and were proved to be the main factor in the swelling. These results demonstrated that the drug release could be controlled by the swelling/deswelling degree of IPN hydrogels as functions of pH and/or temperature. © 1997 John Wiley & Sons, Inc. J Appl Polm Sci 65: 685–693

Pressure sensitive adhesives with good low energy surface adhesion

Abstract: A pressure sensitive adhesive that includes the polymerization product of: (a) 25-97 parts by weight of an acrylic acid ester of a monohydric alcohol whose homopolymer has a Tg less than 0° C.; (b) 3-75 parts by weight of a non-polar ethylenically unsaturated monomer whose homopolymer has a solubility parameter of no greater than 10.50 and a Tg greater than 15° C.; and (c) 0-5 parts by weight of a polar ethylenically unsaturated monomer whose homopolymer has a solubility parameter of greater than 10.50 and a Tg greater than 15° C. The relative amounts of the acrylic acid ester, the non-polar ethylenically unsaturated monomer, and the polar ethylenically unsaturated monomer are chosen such that the 90° peel adhesion of the pressure sensitive adhesive to a polypropylene surface is at least 2 lbs/0.5 in. after a 72 hour dwell at room temperature as measured according to Test Procedure B.

Graft copolymerization of acrylic acid on cellulose: Reaction kinetics of copolymerization

Abstract: Acrylic acid (AA) was grafted to cellulose by using ceric ammonium nitrate (CAN) initiator in aqueous nitric acid solution at 30, 50, 70, and 907C during reaction periods of 30 to 180 minutes. About 45% of the AA was polymerized at 907C after 180 minutes. The grafted polymer and homopolymer were isolated by acetone from the reaction mixture, dried, and subjected to Soxhlet extraction with dioxane to separate the homopolymer, poly(acrylic acid), from the graft copolymer. The water absorption capacities and grafting values of grafted cellulose were also determined. The maximum grafting yield was obtained at 307C. It was also observed that polyacrylic acid-grafted cellulose produced at 307C had the highest water retention capacity. The time depen- dence of AA conversion allowed calculation of first-order reaction rate constants. These rate constants were then used to determine apparent activation energies. q 1997 John Wiley & Sons, Inc. J Appl Polym Sci 66: 929-934, 1997

Thermodynamics of Crew-Cut Micelle Formation of Polystyrene-b-Poly(acrylic acid) Diblock Copolymers in DMF/H2O Mixtures

Abstract: The thermodynamics of formation of “crew-cut” micelles of polystyrene-block-poly(acrylic acid) (PS-b-PAA) diblock copolymers were investigated. The PAA/PS ratios were in the range 0.08−0.33, and N,N-dimethylformamide/water (DMF/H2O) mixtures were used as the selective solvent. For the block ratios investigated here, the copolymers form spherical crew-cut micelles with a large PS core and a thin PAA corona. The temperature dependence of the critical micelle concentration (cmc) was determined under different conditions from scattered light intensity measurements as a function of temperature. The closed association model was found to describe the micellization process and was used to calculate the standard Gibbs free energies (ΔG°), the standard enthalpies (ΔH°), and the standard entropies (ΔS°). The effects of solvent composition, copolymer composition, and added NaCl content on the thermodynamic functions were studied. From the experimental data, a single set of combined equations for the standard thermody...

Reactive Surfactants in Heterophase Polymerization. 9.† Optimum Surfmer Behavior in Emulsion Polymerization

Abstract: In an attempt to define the conditions for the optimum use of polymerizable surfactants (surfmers), two anionic maleate surfmers were applied in various emulsion copolymerization systems including styrene/butyl acrylate/acrylic acid, vinyl acetate/VEOVA 10/acrylic acid, vinyl acetate/butyl acrylate/acrylic acid, and methyl methacrylate/butyl acrylate/vinyl acetate. It was found that the reactivity ratios were the most important variable controlling the incorporation of the surfmer into the polymer chains. The surfmer conversion also depended on the particle size: the larger the particle size, the lower the surfmer conversion. It was also found that when the surfmer copolymerized well with the monomers attaining high conversions from the beginning of the process onward, a significant part of the surfmer was buried in the particle interior, leading to unstable latexes. On the basis of the results, an optimum surfmer behavior was defined. Some preferable combinations of surfmer reactive groups and comonomer...

Adhesive compositions including polyvinylpyrrolidone, acrylic acid polymers, and polyamines

Abstract: A composition comprising a cross-linked salt of (a) a polyvinylpyrrolidone having ring opened pyrrolidone groups; (b) at least one acrylic acid-containing or methacrylic acid-containing polymer; and (c) an amine-containing polymer. The composition may be used as a pressure-sensitive adhesive, has good tack, and may be peeled from the body or from an object without causing damage or injury to the body or object.

Short-Chain Branching Structures in Ethylene Copolymers Prepared by High-Pressure Free-Radical Polymerization: An NMR Analysis

Abstract: It is well-known that short-chain branching (SCB) reactions (intramolecular H-abstraction) play an important role in determining the properties of ethylene homopolymers produced under high pressure by free-radical polymerization. There is little information, however, regarding SCB mechanisms that occur during the synthesis of ethylene copolymers under similar reaction conditions. This work describes SCB structures for a wide range of ethylene copolymers of varying composition (ethylene with n-butyl acrylate (nBA), methyl acrylate (MA), vinyl acetate (VAc), n-butyl methacrylate (nBMA), acrylic acid (AA), and methacrylic acid (MAA)), as determined by proton, 13C, and 2D NMR techniques. Close examination of the resonances reveals that for many (if not all) of these copolymers, a significant fraction of the SCBs contain comonomer as a result of CH2-radical to CH2 backbiting around a comonomer unit. In addition, SCBs are formed not only by hydrogen abstraction from CH2 polyethylene units but also by abstractio...