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Ren D.,Macromolecules and Interfaces Institute | Frazier C.E.,Macromolecules and Interfaces Institute
International Journal of Adhesion and Adhesives | Year: 2012

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.

Fox S.C.,Macromolecules and Interfaces Institute | Edgar K.J.,Macromolecules and Interfaces Institute
Biomacromolecules | Year: 2012

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.

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 | Year: 2013

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.

Pawar S.N.,Macromolecules and Interfaces Institute | Edgar K.J.,Macromolecules and Interfaces Institute
Carbohydrate Polymers | Year: 2013

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.

Wu T.,Macromolecules and Interfaces Institute | Wang D.,Virginia Polytechnic Institute and State University | Zhang M.,Macromolecules and Interfaces Institute | Heflin J.R.,Virginia Polytechnic Institute and State University | And 2 more authors.
ACS Applied Materials and Interfaces | Year: 2012

2-(Dimethylamino)ethyl acrylate (DMAEA) imparts versatile functionality to poly[Sty-b-(nBA-co-DMAEA)-b-Sty] ABA triblock copolymers. A controlled synthetic strategy minimized chain transfer reactions and enabled the preparation of high-molecular-weight ABA triblock copolymers with relatively narrow PDIs between 1.39 and 1.44 using reversible addition-fragmentation chain transfer (RAFT) polymerization. The presence of tertiary amine functionality and their zwitterionic derivatives in the central blocks of the triblock copolymers afforded tunable polarity toward ionic liquids. Gravimetric measurements determined the swelling capacity of the triblock copolymers for ionic liquids (IL) 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMIm TfO) and 1-ethyl-3-methylimidazolium ethylsulfate (EMIm ES). A correlation of differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and small-angle X-ray scattering (SAXS) results revealed the impact of ionic liquid incorporation on the thermal transitions, thermomechanical properties, and morphologies of the triblock copolymers. IL-containing membranes of DMAEA-derived triblock copolymers and EMIm TfO exhibited desirable rubbery plateau moduli of ∼100 MPa and electromechanical actuation to a 4 V electrical stimulus. Maintaining the mechanical ductility of polymer matrices while increasing their ion-conductivity is paramount for future electroactive devices. © 2012 American Chemical Society.

Marks J.A.,Macromolecules and Interfaces Institute | Wegiel L.A.,Purdue University | Taylor L.S.,Purdue University | Edgar K.J.,Macromolecules and Interfaces Institute
Journal of Pharmaceutical Sciences | Year: 2014

Blends of polymers with complementary properties hold promise for addressing the diverse, demanding polymer performance requirements in amorphous solid dispersions (ASDs), but we lack comprehensive property understanding for blends of important ASD polymers. Herein, we prepare pairwise blends of commercially available polymers polyvinylpyrrolidone (PVP), the cationic acrylate copolymer Eudragit 100 (E100), hydroxypropyl methylcellulose acetate succinate (HPMCAS), carboxymethyl cellulose acetate butyrate (CMCAB), hydroxypropyl methylcellulose (HPMC), and the new derivative cellulose acetate adipate propionate (CAAdP). This study identifies miscible binary blends that may find use, for example, in ASDs for solubility and bioavailability enhancement of poorly water-soluble drugs. Differential scanning calorimetry, FTIR spectroscopy, and film clarity were used to determine blend miscibility. Several polymer combinations including HPMCAS/PVP, HPMC/CMCAB, and PVP/HPMC appear to be miscible in all proportions. In contrast, blends of E100/PVP and E100/HPMC showed a miscibility gap. Combinations of water-soluble and hydrophobic polymers like these may permit effective balancing of ASD performance criteria such as release rate and polymer-drug interaction to prevent nucleation and crystal growth of poorly soluble drugs. Miscible polymer combinations described herein will enable further study of their drug delivery capabilities, and provide a potentially valuable set of ASD formulation tools. © 2014 Wiley Periodicals, Inc. and the American Pharmacists Association.

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 | Year: 2012

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.

Wang J.,Virginia Polytechnic Institute and State University | Wang J.,Macromolecules and Interfaces Institute | Nain A.S.,Virginia Polytechnic Institute and State University | Nain A.S.,Macromolecules and Interfaces Institute
Langmuir | Year: 2014

Extracellular matrix (ECM) is a fibrous natural cell environment, possessing complicated micro- and nanoarchitectures, which provide extracellular signaling cues and influence cell behaviors. Mimicking this three-dimensional microenvironment in vitro is a challenge in developmental and disease biology. Here, suspended multilayer hierarchical nanofiber assemblies (diameter from micrometers to less than 100 nm) with accurately controlled fiber orientation and spacing are demonstrated as biological scaffolds fabricated using the non-electrospinning STEP (Spinneret based Tunable Engineered Parameter) fiber manufacturing technique. Micro/nanofiber arrays were manufactured with high parallelism (relative angles between fibers were maintained less than 6°) and well controlled interfiber spacing (<15%). Using these controls, we demonstrate a bottom up hierarchical assembly of suspended six layer structures of progressively reduced diameters and spacing from several polymer systems. We then demonstrate use of STEP scaffolds to study single and multicell arrangement at high magnifications. Specifically, using double layer divergent (0°-90°) suspended nanofibers assemblies, we show precise quantitative control of cell geometry (change in shape index from 0.15 to 0.57 at similar cell areas), and through design of scaffold porosity (80 × 80 μm2 to 5 × 5 μm2) quadruple the cell attachment density. Furthermore, using unidirectional or crisscross patterns of sparse and dense fiber arrays, we are able to control the cell spread area from ∼400 to ∼700 μm2, while the nucleus shape index increases from 0.75 to 0.99 with cells nearly doubling their focal adhesion cluster lengths (∼15 μm) on widely spaced nanofiber arrays. The platform developed in this study allows a wide parametric investigation of biophysical cues which influence cell behaviors with implications in tissue engineering, developmental biology, and disease biology. © 2014 American Chemical Society.

Gao R.,Macromolecules and Interfaces Institute | Wang D.,Virginia Polytechnic Institute and State University | Heflin J.R.,Virginia Polytechnic Institute and State University | Long T.E.,Macromolecules and Interfaces Institute
Journal of Materials Chemistry | Year: 2012

Block copolymer-ionic liquid composite materials emerge as promising candidates for electromechanical transducer applications. Herein, a novel imidazolium sulfonate-containing pentablock copolymer-ionic liquid composite was prepared and fabricated into thermally stable electroactive actuators, which exhibit effective actuation response under a low applied potential of 4 V. © 2012 The Royal Society of Chemistry.

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