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Query: UMLS:C0267964 (PAA)
 2,561 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The mechanism of morphological phase transitions was studied for rod-shaped supramolecular assemblies comprised of a poly(acrylic acid)-block-poly(methyl acrylate)-block-polystyrene (PAA(90)-b-PMA(80)-b-PS(100)) triblock copolymer in 33% tetrahydrofuran/water after perturbation by reaction with a positively charged water-soluble carbodiimide. Tetrahydrofuran solvation of the hydrophobic core domain provided the dynamic nature required for the rod-to-sphere phase transition to be complete within 30 min. The intermediate morphologies such as fragmenting rods and pearl-necklace structures were trapped kinetically by the subsequent addition of a diamino crosslinking agent, which underwent covalent crosslinking of the shell layer. Alternatively, shell-crosslinked rod-shaped nanostructures with preserved morphology were obtained by the addition of the crosslinking agent before the addition of the carbodiimide, which allowed for the shell crosslinking to be performed at a faster rate than the morphological reorganization. The formation of robust shell-crosslinked nanostructures provides a methodology by which the morphological evolution processes can be observed, and it allows access to otherwise thermodynamically unstable nanostructures.
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PMID:Chemically induced supramolecular reorganization of triblock copolymer assemblies: trapping of intermediate states via a shell-crosslinking methodology. 1192 63

Nanostructured polyelectrolyte multilayer thin films electrostatically assembled alternately from such polymers as poly(allylamine hydrochloride) (PAH) and poly(acrylic acid) (PAA) were investigated for their in vitro cell interactions. Not surprisingly, NR6WT cells, a highly adhesive murine fibroblast cell line, attached to many different multilayer combinations tested. However, PAH/PAA multilayers constructed at pH deposition conditions of 2.0/2.0 were completely bioinert. Analogous cell interactions were observed with PAH/poly(methacrylic acid) (PAH/PMA), PAH/sulfonated poly(styrene) (PAH/SPS), and poly(diallyldimethylammonium chloride)/SPS (PDAC/SPS) systems, thereby suggesting a general trend in the fibroblasts' response to multilayers. Specifically, highly ionically stitched films attracted cells, whereas weakly ionically cross-linked multilayers, which swell substantially in physiological conditions to present richly hydrated surfaces, resisted fibroblast attachment. Thus, by manipulating the multilayer pH or ionic strength assembly conditions or both, which in turn dictate the molecular architecture of the thin films, one may powerfully direct a single multilayer combination to be either cell adhesive or cell resistant.
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PMID:Rational design of cytophilic and cytophobic polyelectrolyte multilayer thin films. 1252 53

Hydrogen-bonded multilayers comprised of polyacrylamide (PAAm) and a weak polyelectrolyte, such as poly(acrylic acid) (PAA) or poly(methacrylic acid) (PMA), were investigated for their surface-cell interactions. The assembled films were lightly cross-linked thermally or photochemically in order to render them stable in a physiological environment. Both PAA/PAAm and PMA/PAAm multilayers were found to exhibit a high resistance to the adhesion (cytophobicity) of mammalian fibroblasts, even with only a single bilayer coating. Protein adsorption to the multilayers, as revealed by surface plasmon resonance measurements, was greatly reduced for fibronectin and serum-containing medium. In situ swelling experiments indicate that the H-bonded multilayers are hydrogellike coatings capable of a high level of swelling in buffered solution. Utilizing the H-bonding nature of these multilayers, we were able to micropattern the films to create more complex cell-resistant/-adhesive surfaces. The long-term stability of the cell-resistant multilayers was found to be exceptionally good even under conditions (pH 7.4, buffered solution) where a high degree of swelling takes place. No degradation of the micropatterned films was observed over a period of a month, during which time the multilayer coatings remained highly resistant to cell-adhesion.
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PMID:New class of ultrathin, highly cell-adhesion-resistant polyelectrolyte multilayers with micropatterning capabilities. 1285 83

Shell cross-linked nanoparticles (SCKs) presenting surface- and bioavailable biotin functional groups were synthesized via a mixed micelle methodology, whereby co-micellization of chain terminal biotinylated poly(acrylic acid)-b-poly(methyl acrylate) (PAA-b-PMA) and nonbiotinylated PAA-b-PMA were cross-linked in an intramicellar fashion within the shell layer of the mixed micelles, between the carboxylic acid groups of PAA and the amine functionalities of 2,2'-(ethylenedioxy)diethylamine. The hydrodynamic diameters (D(h)) of the micelles and the SCKs with different biotinylated block copolymer contents were determined by dynamic light scattering (DLS), and the dimensions of the SCKs were characterized with tapping-mode atomic force microscopy (AFM) and transmission electron microscopy (TEM). The amount of surface-available biotin was tuned by varying the stoichiometric ratio of the biotinylated PAA-b-PMA versus the nonbiotinylated PAA-b-PMA, as demonstrated with solution-state, binding interaction analyses, an avidin/HABA (avidin/4'-hydroxyazobenzene-2-carboxylic acid) competitive binding assay, and fluorescence correlation spectroscopy (FCS). The avidin/HABA assay found the amount of available biotin at the surface of the biotinylated SCK nanoparticles to increase with increasing biotin-terminated block copolymer incorporation, but to be less than 25% of the theoretical value. FCS measurements showed the same trend.
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PMID:Determination of the bioavailability of biotin conjugated onto shell cross-linked (SCK) nanoparticles. 1516 Dec 88

Disk and cylindrical micellar assemblies were formed through self-organization of poly(acrylic acid)-b-poly(methyl acrylate)-b-polystyrene (PAA-b-PMA-b-PS) amphiphilic triblock copolymers with organic diamines as counterions in water/ tetrahydrofuran (THF) solvent mixtures. The system was investigated by means of transmission electron microscopy and cryogenic transmission electron microscopy. It was found that the assembled-state morphologies could be modified by alteration of the type and concentration of cationic diamine counterion undergoing interaction with the negatively charged, polyelectrolyte PAA corona block, the relative amount of water in the water/THF mixture, and the hydrophobic block chain length. Multivalency of the organic amine counterion was critical for disk formation. It was further demonstrated that a single block copolymer underwent disc-to-cylindrical micellar transitions reversibly with variation in the relative water/THF ratio. The ability to form disks beginning from either THF-rich or water-rich solutions indicated that the disk morphology was thermodynamically stable and that THF was important in keeping the micellar structure from becoming kinetically frozen. The nanoassemblies were produced having low size dispersities and were stable for at least one month. Intermediate structures between disks and cylinders were also observed, indicating two distinct kinetic pathways between the two micelle structures.
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PMID:Disk morphology and disk-to-cylinder tunability of poly(acrylic acid)-b-poly(methyl acrylate)-b-polystyrene triblock copolymer solution-state assemblies. 1604 91

Poly(methyl acrylate)-grafted poly(methyl-n-propylsilane) (PMPrS-g-PMA) and poly(acrylic acid)-grafted PMPrS (PMPrS-g-PAA) were synthesized by gamma-ray-induced graft polymerization, and the association behavior of these graft copolymers was investigated in selective solvents composed of good and poor solvents for the PMPrS main chain. Fluorescence spectroscopy with perylene as a fluorescent probe revealed that PMPrS-g-PAA in a water/THF mixed solvent self-assembles into micelles with a swollen core of PMPrS chains in the water content range of 50-95%. UV spectroscopy demonstrated that a further increase of the water content gives rise to the conformational transition of the PMPrS chains in the micelle core from the random conformation to the conformation that corresponds to that in the solid state at a water content of ca. 95%, independent of the grafting yield. Similar behavior was also observed in DMSO/THF solutions of PMPrS-g-PMA, for which the conformational transition occurred at the constant DMSO content of ca. 95%. These results indicate that solvatochromic behavior of polysilane, which is a characteristic feature of polysilane, proved to provide information on the inner structure of those micelles: PMPrS chains in the core undergo conformational transition as the content of the poor solvents for PMPrS increases, while maintaining the micelle structure.
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PMID:Conformational transition of the core chain in radiation-modified polysilane micelles formed in selective solvents. 1608 71

Interaction of Ca(2+) ions with poly(acrylic acid) (PAA) or poly(methacrylic acid) (PMA) was studied using a Ca(2+) ion sensitive electrode. When the PAA solution was neutralized with Ca(OH)(2), the Ca(2+) activity had a maximum around the degree of neutralization 0.5 and decreased with further increase of Ca(OH)(2), being similar to the behavior of the Ca(2+) activity in a maleic acid copolymer solution as reported previously. When the polymer concentration was as low as 0.1 mM, this peak in the Ca(2+) activity was not observed and the counterion condensation theory held. The decrease of the Ca(2+) activity in PAA solution at the degree of neutralization unity was depresseed by the presence of several millimolar KCl. The Ca(2+) activity in the PAA solution at the low degree of neutralization was increased by the presence of dilute KCl and decreased by the presence of concentrated KCl. The decrease of the Ca(2+) activity in PMA solution was observed also at the degree of neutralization unity, but its extent was small compared with that of the PAA solution and the maximum of the Ca(2+) activity was shifted to the degree of neutralization 0.75. The effects of KCl on the Ca(2+) activity in the PMA solution were almost the same as those in the PAA solution. Interpretations of the behavior of the Ca(2+) activity were discussed.
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PMID:Interaction of calcium ions and polyelectrolytes. 1702 36

The amidase reaction of trypsin, which is a member of the serine proteinase family, is accelerated by its complexation with block ionomers containing a polycarboxylate block, such as PEG-PAA, PEG-PGA, or PEG-PMA. PEG-PAA and PEG-PGA had similar effects, causing an increase in the k(cat) value and a shift in the pH profile to a lower pH region. On the other hand, PEG-PMA showed not only an increase in the k(cat) value, but also a decrease in the activation energy; however, there was no shift in the pH dependence of the initial reaction rate. Such differences might be induced by the difference in pK(a) values of the polycarboxylate block in block ionomers.
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PMID:Effect of polycarboxylate blocks on the amidase activity of trypsin through complexation with PEG/polycarboxylate block ionomers. 1737 Feb 72

Using poly(acrylic acid)-b-poly(methyl acrylate)-b-polystyrene (PAA-b-PMA-b-PS) triblock copolymers or a mixture of different molecular weight PAA-b-PS diblock copolymers, stacks of polymeric micellar assemblies, such as disks and Y-shaped cylinders, were formed through intermicellar interactions. Whereas micelles hierarchically stacked together, micellar interactions within the stack defined a uniform micelle geometry and size for up to micrometers in length. The kinetic pathway dependence and stability of the stacked assemblies were studied, and possible intermicellar interactions between micelles within the stacks are proposed.
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PMID:Controlled stacking of charged block copolymer micelles. 1739 96

A thiol-ene polymerization was accomplished on silicate glass slides to graft a series of homopolymers and copolymers using 3-(mercaptopropyl)trimethoxysilane (MTS) as both a silane coupling agent and initiator. MTS was initially covalently bonded to an acid cleaned glass surface via a classical sol-gel reaction. Poly(acrylic acid) (PAA), poly(acrylamide) (PAAm), poly(methyl acrylate) (PMA), poly(acrylamido-2-methyl-propanesulfonic acid) (PAMPS), and the copolymer poly(AA-co-AAm-co-MA-co-AMPS) were grafted from the thiol group of MTS. The surface chemistry of the MTS modified slides and polymer grafts was characterized with attenuated total reflection Fourier transform infrared (ATR-FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). Surface texture was evaluated with tapping mode atomic force microscopy (TM-AFM). The Owens-Wendt-Kaelble (OWK) and Lifshitz-van der Waals acid-base (LW-AB) methods were used to evaluate surface energies by sessile drop contact angle method. The synthetic approach demonstrated a facile, rapid method for grafting to glass surfaces.
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PMID:Surface modification of silicate glass using 3-(mercaptopropyl)trimethoxysilane for thiol-ene polymerization. 2187 Jul 97


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