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Haupt R.A.,Macromolecules and Interfaces Institute | Renneckar S.,Macromolecules and Interfaces Institute | Renneckar S.,Virginia Polytechnic Institute and State University
Magnetic Resonance in Chemistry

Alkali metal counter-cations alter the electron density of phenolates in solution by electrostatic interactions. This change in electron density affects their reactivity toward formaldehyde, hydroxymethylphenols, and isocyanates during polymerization. The electronic perturbation of phenolic model compounds in the presence of alkali metal hydroxides was investigated with 13C and 1H nuclear magnetic resonance in polar solvents relative to non-ionic controls, altering the chemical shifts of the model compounds, thus indicating changes in electron density using the chemical shift as a proxy. These shifts were attributed to Coulombic electrostatic interactions of the counter-cation with the phenolate anion that correlated to hydrated ionic radius and solvent dielectric constants. The predicted relative reaction rates for formaldehyde addition based on electron density ranking from 13C nuclear magnetic resonance of the phenolic models was compared with the literature values. Predictions for condensation reactions of 2- and 4-hydroxymethylphenol from chemical shifts were consistent with published results. The results permit predictions for the reaction of phenolic compounds for the formation of thermosetting polymeric materials. Copyright © 2012 John Wiley & Sons, Ltd. Source

Pawar S.N.,Macromolecules and Interfaces Institute | Edgar K.J.,Macromolecules and Interfaces Institute
Carbohydrate Polymers

Alginates are (1 → 4) linked linear copolysaccharides composed of β-d-mannuronic acid (M) and its C-5 epimer, α-l-guluronic acid (G). Several strategies for synthesis of carboxyl modified alginate derivatives exist in the literature. Most of these however employ aqueous chemistries, such as carbodiimide coupling reactions. Based on our recently discovered method for homogeneous dissolution of tetrabutylammonium (TBA)-alginate, we now describe use of tetrabutylammonium fluoride (TBAF)-based two component solvent systems as media for synthesis of carboxyl-modified alginate esters. Partially and fully esterified benzyl, butyl, ethyl, and methyl alginates were synthesized via reaction with the corresponding alkyl halides. The newly synthesized derivatives were soluble in polar aprotic solvents without the addition of TBAF. Saponification was performed to demonstrate that alkylation was completely regioselective for carboxylate groups in preference to hydroxyl groups to form esters. We demonstrate the utility of these alginate esters to enhance aqueous solubility of the flavonoid naringenin by formation of solid dispersions. © 2013 Elsevier Ltd. All rights reserved. Source

Fox S.C.,Macromolecules and Interfaces Institute | Edgar K.J.,Macromolecules and Interfaces Institute

Aminated polysaccharides have been extensively investigated for a wide range of biomedical applications. To achieve targeted properties such as solubility and miscibility, it can be beneficial to modify the polysaccharide hydroxyl groups selectively while leaving the amino groups unmodified. This tends to be difficult because of the higher reactivity of primary amines than hydroxyl groups toward electrophilic reagents. We describe herein a new method that can produce O-acylated, aminated polysaccharides with extremely high selectivity. In this procedure, 6-azido-6-deoxy-cellulose esters are synthesized from 6-bromo-6-deoxy-cellulose esters. The azide groups are then selectively and mildly reduced using the Staudinger reaction to produce 6-amino-6-deoxy-2,3- di-O-acyl-cellulose derivatives. This demonstrates the effectiveness of the Staudinger reduction on a polysaccharide substrate in the presence of easily reducible ester groups. © 2012 American Chemical Society. Source

Ren D.,Macromolecules and Interfaces Institute | Frazier C.E.,Macromolecules and Interfaces Institute
International Journal of Adhesion and Adhesives

Two moisture-cure polyurethane adhesives (PURs) were studied: a model (MPUR) prepared from a symmetrical diisocyanate that gave rise to a continuous soft phase, and a commercially relevant adhesive (CPUR) prepared from an asymmetrical polyisocyanate that resulted in a continuous hard phase. Atomic force microscopy revealed that the size and size distributions of the respective dispersed phases were altered by wood, as observed in localized specimen regions. Bulk effects were observed with dynamic mechanical analysis; both soft and hard phase MPUR relaxations were altered by wood (increased transition temperatures), whereas only the continuous CPUR hard phase revealed wood-induced changes. Furthermore, infrared analysis showed that wood promoted the formation of hydrogen-bonded urea structures in CPUR bondlines. Significant wood/PUR interactions were detected, however it was not possible to determine if the effects arose from direct intermolecular associations, or from indirect effects arising from the mere presence of wood and how this impacts forces acting upon the liquid adhesive (i.e. moisture transport, differing interfacial energies through which transport occurs, and CO 2 bubble nucleation). Regardless, it is clear that PUR studies should be conducted under conditions that simulate real wood/PUR bondlines. © 2012 Elsevier Ltd. Source

Buckwalter D.J.,Macromolecules and Interfaces Institute | Sizovs A.,Macromolecules and Interfaces Institute | Ingle N.P.,University of Minnesota | Reineke T.M.,University of Minnesota
ACS Macro Letters

Herein, we demonstrate the reversible addition-fragmentation chain transfer (RAFT) synthesis of an adamantane-conjugated glycopolymer, poly(2- methacrylamido-2-deoxy glucopyr-anose) (Ad-pMAG), as a hydrophilic coating to promote colloidal stability of click cluster-pDNA complexes in biological media. The Ad-pMAG is assembled via noncovalent interactions through inclusion complex formation between adamantane (Ad) and the β-cyclodextrin (βCD) core of the click cluster/pDNA and then further assembled with plasmid DNA to form polyplexes. Ad-pMAG incorporation was favorable over Ad-poly(ethylene glycol) (Ad-PEG) due to the enhanced colloidal stability of the click cluster/pDNA polyplex under physiological salt conditions at high N/P ratios. Interestingly, the uptake and reporter gene expression with polyplexes coated with the Ad-pMAG was much lower in HeLa cells than that observed with two glioma cell lines (U87 and U251 cells) in vitro, possibly indicating some delivery specificity. (Figure presented) © 2012 American Chemical Society. Source

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