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ABSTRACT: When making nanocomposites, there is a big challenge to obtain both functional and mechanical enhancement. In this study, a new in situ polymerization methodology for the incorporation of surface modified silver nanoparticles (AgNPs) in a thermoplastic polyurethane matrix was developed. AgNPs with contents ranging from 0 to 1.5 wt % were used. A double functionalization of the nanoparticles with oleic acid was performed, which lead to a reaction of carboxylic acid groups in the nanoparticle's surface with isocyanate groups of the 4,4′‐methylene diphenyl diisocyanate monomer as corroborated from the Raman results. The successful incorporation of the nanoparticles was verified with EDS, TGA, and Raman measurements. Thermal properties of nanocomposites were investigated by DSC. AgNPs made positive impact in two ways: first, increased more than twice the elastic modulus, as studied via nanoindentation measurements and second, based on the inhibition zone method, great bactericidal effectiveness for nanocomposites containing 1.5 wt % AgNPs was observed for Escherichia coli. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018, 135, 46180. [ABSTRACT FROM AUTHOR]

This work investigates the two-step polymerization between methylene diphenyl diisocyanate (MDI), two different poly(tetramethylene oxide) macrodiols, and 1,4-butanediol (BD) as chain extender. At the end of the prepolymerization, the reaction mixture contains MDI in excess and a prepolymer with isocyanate end group. Then, BD and a solvent (tetrahydrofuran) were added to start the finishing stage under nominal stoichiometric equilibrium. The reaction was analyzed by Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance (1H-NMR), and size exclusion chromatography. 1H-NMR was employed to follow global concentrations of unreacted isocyanate end groups and internal urethane groups. This information enabled to estimate the following "effective" rate constants: k1 =1.07 x 10-3 L mol-1 s-1 for the prepolymerization; and k2=1.94 x 10-4 L mol-1 s-1 for the finishing stage. These values are subject to errors caused by biases introduced in the recipe, in the measurements, in the reaction conditions, in the quality of reagents, and in the reaction mechanism assumptions. Such errors also explain the dispersion of the published rate constants values. The ¹H-NMR measurements also enabled to estimate the evolution (with extent of reaction) of the numberaverage number of structural units along the prepolymerization and finishing stages; and such estimates reasonably verify Flory's classical expressions. [ABSTRACT FROM AUTHOR]

An investigation on the cooling-induced crystallization in three thermoplastic polyurethanes based on MDI, PTMG, and 1.4-BD as chain extender with different hard segment content is reported. Thermal transitions were determined using differential scanning calorimetry (DSC) measurements at different cooling rates, and thermal stability was studied by thermogravimetric analysis. Changes in Raman spectra were useful to correlate the thermal transitions with changes in the morphology of the polymers. The dissimilarity in the composition gave different rheological behavior in the molten state, indicated by the temperature dependence of the viscosity. The mechanical properties and the crystallinity was influenced not only by the cooling rate but also by the hard segment content. Thermoplastic polyurethanes with more hard segment content formed more crystalline hard domains as evidenced by the DSC and atomic force microscopy results. [ABSTRACT FROM AUTHOR]

ABSTRACT Novel segmented polyurethane elastomers were successfully synthesized by a nonisocyanate route using dicyclic carbonates as precursors for both soft and hard segments. The hard segment was prepared from the dicyclic carbonate of bisphenol A and m-xylylenediamine as chain extender. The soft segment was poly(tetramethylene ether) glycol of molecular weight 1000. Three polyurethanes with different morphologies were made with soft segment concentration of 70, 50, and 30%. Method of synthesis consisted in preparation of dicyclic carbonate of bisphenol A from a commercial epoxy resin and carbon dioxide, while dicyclic carbonate of poly(tetramethylene ether) glycol (PTMEG) was made from previously prepared diglycidyl ether of PTMEG and carbon dioxide. Polymers were prepared by reacting dicyclic carbonates with m-xylylenediamine by one-pot process. The monomers and polymers were characterized by Fourier transform infrared spectroscopy, differential scanning chromatography, thermogravimetric analysis, 1H NMR, 13C NMR, scanning electron microscopy, and mechanical measurements. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42492. [ABSTRACT FROM AUTHOR]