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

Based on the premise that similar surface properties between the adhesive and the substrate would yield a strong adhesive bond, copolymers of acrylic acid (AA) and 2-ethylhexyl acrylate (EHA), P(AA-co-EHA), were designed and synthesized for buccal mucoadhesion. A series of linear copolymers with varying feed ratios of the two monomers (AA and EHA) were synthesized through free radical copolymerization at 69+/-0.5 degrees C using azobis(isobutyronitrile) (AIBN) as initiator. The reactions were carried out in THF under nitrogen for 24 h. The glass transition temperatures, T(g), of the copolymers were determined using DSC. The adhesion studies were conducted to determine the effects of copolymer composition, contact time between the substrate and the adhesive, and crosshead speed on mucoadhesive performance of the copolymer films using a computer interfaced Instron material testing system. The glass transition temperature of the copolymers decreased with increasing EHA content. Wet glass surface as substrate was shown not to be a good substrate model for adhesion determination studies. The copolymer composed of 46:54 mol.% AA:EHA (an almost 1:1 ratio in the repeat units) yielded the highest mucoadhesive force in contact with porcine buccal mucosa which was significantly greater (P<0.05) than that of poly(acrylic acid) (PAA) (used as positive control). The mucoadhesive force for all copolymers studied was significantly (P<0.05) greater than that of the negative control (backing material without copolymer film) except for the EHA homopolymer. Crosshead speed increased mucoadhesive force linearly and had a more pronounced effect on the mucoadhesive performance than time of contact between the adhesive and the substrate.
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PMID:Evaluation of poly(acrylic acid-co-ethylhexyl acrylate) films for mucoadhesive transbuccal drug delivery: factors affecting the force of mucoadhesion. 1082 56

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

The aggregate morphologies of the biamphiphilic triblock PAA(26)-b-PS(890)-b-P4VP(40) have been studied by TEM as a function of pH in DMF/THF/H(2)O mixtures. The outside surfaces of the aggregates were characterized by zeta potential measurements. Starting at the apparent pH (pH) of 1, and increasing gradually to pH14, the aggregate morphologies of this triblock change progressively from vesicles (pH1), to solid spherical or ellipsoidal aggregates (pH3 approximately 11), and finally back to vesicles (pH14). Vesicles prepared at pH1 contain P4VP chains on the outside and PAA chains on the inside, while those prepared from the same triblock at pH14 contain PAA outside and P4VP inside. The segregation is based on the difference in repulsive interactions within the PAA or P4VP corona under different pH conditions. At low pH, the curvature is stabilized through increased repulsive interactions between the P4VP chains on the outside relative to the less repulsive interactions between the PAA chains on the inside. At pH14, by contrast, the PAA is preferentially segregated to the outside and the P4VP to the inside because of the increased repulsive interaction between PAA chains and the decreased repulsive interaction between P4VP chains at high pH. Most importantly, vesicles with PAA on the outside can be inverted to P4VP on the outside by changing the pH while the vesicles have swollen cores and are under dynamic conditions. The conversion mechanism is suggested to involve a whole vesicle process because the CMC is far too low for single chain reassembly to be involved.
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PMID:Preparation and pH triggered inversion of vesicles from poly(acrylic acid)-block-polystyrene-block-poly(4-vinyl pyridine). 1465 40

Cadmium sulfide (CdS) quantum dots (QDs) are formed within poly(ethylene oxide)-block-polystyrene-block-poly (acrylic acid) (PEO-b-PS-b-PAA) triblock copolymer aggregates of different architectures. These structures are obtained starting with the same ionically cross-linked primary micelles consisting of a cadmium acrylate core, a PS shell, and a PEO corona. One morphology is a worm-shaped micelle prepared in tetrahydrofuran (THF) in which the CdS QDs are surrounded by the PAA and aligned as a loose necklace in the PS matrix. The PEO serves as a corona around the PS rod. Another structure is a multicore spherical (ca. 50 nm) water soluble PS micelle, surrounded by PEO chains. The CdS particles within these two latter structures are formed by the reaction of cadmium ions present in the acrylate cores with hydrogen sulfide. In a third structure, the CdS QDs are located on the surface of PS micelles. A fourth spherical single-core micelle structure is postulated to exist in dilute THF solutions. The dimensions in all the aggregates can be controlled by the block length.
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PMID:Cadmium sulphide quantum dots in morphologically tunable triblock copolymer aggregates. 1601 70

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

Antigen-decorated shell cross-linked knedel-like nanoparticles (SCKs) were synthesized and studied as multivalent nanoscale surfaces from which antibody-binding units were presented in a manner that was designed to approach virus particle surfaces. The SCK nanostructures were fabricated with control over the number of antigenic groups, from mixed micellization of amphiphilic diblock copolymer building blocks that contained either an antigen (2,4-dinitrophenyl) or an ethylpropionate group at the hydrophilic alpha-chain terminus. Amphiphilic diblock copolymers were synthesized by atom transfer radical polymerization of tert-butyl acrylate and methyl acrylate sequentially from either a 2,4-dinitrophenyl-functionalized initiator or ethyl 2-bromopropionate, followed by selective removal of the tert-butyl groups to afford 2,4-dinitrophenyl-poly(acrylic acid)60-b-poly(methyl acrylate)60 (DNP-PAA(60)-b-PMA60) and poly(acrylic acid)70-b-poly(methyl acrylate) (PAA70-b-PMA70). Micelles were assembled via addition of water to THF solutions of the polymers in 0:1, 1:1, and 1:0 molar ratios of DNP-PAA60-b-PMA60 to PAA70-b-PMA70, followed by dialysis against water. The acrylic acid groups of the micelle coronas were partially cross-linked (nominally 50%) with 2,2'-(ethylenedioxy)bis(ethylamine), in the presence of 1-(3'-dimethylaminopropyl)-3-ethylcarbodiimide methiodide. Following extensive dialysis against water, the 0%, 50%, and 100% dinitrophenylated shell cross-linked nanoparticles (DNP-SCKs) were characterized with dynamic light scattering (DLS), transmission electron microscopy (TEM), atomic force microscopy (AFM), differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), infrared and UV-vis spectroscopies, and analytical ultracentrifugation (AU). The surface accessibility and bioavailability of the DNP units upon the DNP-SCKs were investigated by performing quenching titrations of fluorescein-labeled IgE antibody in solution and degranulation of IgE sensitized RBL-2H3 cells. The DNP antigens proved to be surface-available and able to form multivalent bonds with IgE antibodies, causing degranulation.
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PMID:Antigen-decorated shell cross-linked nanoparticles: synthesis, characterization, and antibody interactions. 1617 5

The water content-dependent supramolecular structure formation of polystyrene-block-poly(acrylic acid) (PS-b-PAA) copolymer in the presence of a fourth-generation amine-terminated poly(amido amine) dendrimer (PAMAM) is investigated by dynamic light scattering, turbidity measurements, and transmission electron microscopy. The solvent system for this study is a mixture of dioxane/THF and water. A very complex turbidity profile is observed with increasing water content in the system and is explained by the presence of various aggregated structures based on strong interactions between the amine-containing dendrimers and the poly(acrylic acid) blocks of the polymer. The onset of the self-assembly of single chains of PS-b-PAA (primary structure) into single and multiple dendrimer core inverse micelles (secondary structure) is detected as very low water contents of cw < 2% wt (cwc). These micelles consist of dendrimers coated with PAA blocks, which are connected to the corresponding PS chains that form the corona. Further addition of water leads to an association of these micelles into compound multiple dendrimer core inverse micelles (tertiary structure) in the range of cw = approximately 6 to approximately 10% wt. At still higher water content, some of the acrylic acid chains of the block copolymer move from the vicinity of the dendrimer to the outside of the aggregates, resulting in a decrease in the size of the formed structures and the acquisition of progressively increasing hydrophilic character of the aggregates. Multiple dendrimer core inverse onion micelles are formed, which agglomerate into compound multiple dendrimer core inverse onion micelles at cw = approximately 12 to approximately 18% wt. Above this water content, vesicular structures are formed. The complexity is unusual for block copolymer systems and illustrates the importance of strong interactions in structure formation.
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PMID:Dendrimer-influenced supramolecular structure formation of block copolymers. 1782 25

The dendrimer concentration dependence of the supramolecular structure formation of polystyrene-block-poly(acrylic acid) in dioxane/THF was investigated as a function of water content. The distribution as well as the localization of the dendrimer units inside the formed aggregates were determined by comparative studies of turbidity measurements and transmission electron microscopy. The strong and specific interactions present between the amine groups of the dendrimer (PAMAM) and the carboxylic acid residues of PAA in the copolymer have a strong influence on the structure formation. The PAMAM concentration as well as the character of the terminal groups of the dendrimer influence the strength of these interactions and consequently affect the structure formation process. As shown by fluorescence quenching experiments, on all supramolecular hierarchical structure levels, and specifically in vesicles, the dendrimer is coated by the PAA chains of the block copolymer due to the strong interactions; since the PAA blocks are connected to the PS blocks, which form the corona, the dendrimer is surrounded by PS chains and is thus encapsulated into the hydrophobic regions of the block copolymer aggregates. A high-resolution transmission electron microscopy image of a micelle is shown, in which the individual dendrimer cores are seen to be localized in the center of these aggregates, and thus, the structure proposed in the previous publication (Kroeger, A.; Li, X.; Eisenberg, A. Langmuir 2007, 23, 10732) is confirmed. Furthermore, the sizes of the resulting aggregates depend on the relative concentration of dendrimer, expressed as RAm/Ac (the ratio of amine to acid groups). With increasing RAm/Ac values, not only the sizes of the micelles but also the vesicle dimensions, especially vesicle wall thicknesses, increase, and this effect suggests the encapsulation of the dendrimer into the vesicle walls. Thus, the constitution of the vesicle structure is determined precisely. This feature allows the potential incorporation of a wide range of species into the vesicle walls or the center of the micelle cores.
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PMID:Dendrimer influenced supramolecular structure formation of block copolymers: II. Dendrimer concentration dependence. 1823 5

Hydrophobic lead sulfide quantum dots (PbS/OA) synthesized in the presence of oleic acid were transferred from nonpolar organic solvents to polar solvents such as alcohols and water by a simple ligand exchange with poly(acrylic acid) (PAA). Ligand exchange took place rapidly at room temperature When a colloidal solution of PbS/OA in tetrahydrofuran (THF) was treated with excess PAA, the PbS/PAA nanocrystals that formed were insoluble in hexane and toluene but could be dissolved in methanol or water, where they formed colloidal solutions that were stable for months. Ligand exchange was accompanied by a small blue shift in the band-edge absorption, consistent with a small reduction in particle size. While there was a decrease in quantum yield associated with ligand exchange and transfer to polar solvents, as is commonly found for colloidal quantum dots, the quantum yields determined were impressively high: PbS/OA in toluene (82%) and in THF (58%); PbS/PAA in THF (42%) and in water (24%). The quantum yields for the PbS/PAA solutions decreased over time as the solutions were allowed to age in the presence of air.
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PMID:Highly luminescent lead sulfide nanocrystals in organic solvents and water through ligand exchange with poly(acrylic acid). 1859 1


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