In Situ Quenching Methods Toward exo-Olefin-Terminated Polyisobutylene

exo-Olefin-terminated polyisobutylene was obtained directly from living isobutylene polymerizations by addition of a quenching compound to the living chain ends. Three broad classes of compounds were evaluated including hindered bases such as hindered pyridines and piperidines, N-hydro-2,5-disubstitutedpyrroles, and sulfides, ethers, and silylethers. The proposed mechanism of quenching unique to each class was discussed, with supporting kinetic, spectroscopic, and structure-based evidence presented. Hindered bases were proposed to operate by E2 elimination reaction of free base at the carbenium ion. N-Hydro-2,5-disubstitutedpyrroles were proposed to form the η⁵-2,5-disubstitutedpyrrolyltrichloro-titanium(IV) coordination complex, which serves as the true quencher. Sulfides, ethers, and silylethers were proposed to operate by first converting the PIB chain ends quantitatively to the onium adduct, which is then decomposed to form exo-olefin PIB. Sulfides and ethers were the best performing quenchers of all the types studied, particularly bulky ones such di-tert-butylsulfide and diisopropyl ether.     

The energy-critical quantum harmonic oscillator

We consider the energy critical nonlinear Schrödinger equation in dimensions 3 and above with a harmonic oscillator potential. In the defocusing situation, we prove global wellposedness for all initial data in the energy space Σ. This extends a result of Killip-Visan-Zhang, who treated the radial case. For the focusing nonlinearity, we obtain wellposedness for data in Σ satisfying an analogue of the usual size restriction in terms of the ground state W. We implement the concentration compactness variant of the induction on energy paradigm and, in particular, develop profile decompositions adapted to the harmonic oscillator.     

The keto-enol tautomerization of ethyl butylryl acetate studied by LC-NMR

The keto-enol tautomerism of ethyl butylryl acetate was studied in mixed solvents under a variety of experimental conditions. The direct measurement of ketonization of the enol tautomer was performed by using the hyphenated technique LC-NMR. The keto and enol tautomers can be separated by using HPLC and their interconversion is a slow process on the NMR timescale. The ketonization reaction was found to be acid catalyzed and the solvent isotope effect, kH2O/kD2O, in an acetonitrile/water mixture, is 5.4. The ketonization rate constants were also measured at different compositions of binary solvents, such as CH3CN/D2O, CD3OD/D2O, and CH3CN/CD3OD. The rate constant and water percentage were found to have an exponential relationship. The reaction rate as a function of solvent polarity will be discussed in this paper.     

STRUCTURAL EVOLUTION IN BIORENEWABLE SOY BASED POLYURETHANES

Spectroscopic studies have revealed that the amount of polyureas formed and the kinetics of their formation in soy based polyurethane systems are considerably different from traditional systems employing ethylene oxide-propylene oxide (EO-PO) based polyols.The aggregation of polyureas was characterized by the hydrogen bonds formed utilizing FTIR spectroscopy.This study offered the opportunity to assign the previously undefined infrared features.The structural transformation is reflected in the segmental ...     

A Comparison of the Fluorescence Spectra of Murine and Bovine Central Nervous System and Other Tissues

We describe a comparison of the fluorescence spectra of bovine tissues with murine tissues in order to determine whether spectral features are conserved and whether an appropriate and practical laboratory small animal model system could be identified to be used for investigation of tissue- and age-related fluorescence signal patterns. Recently it has been shown that spectral signatures of lipofuscin have enabled the detection of bovine central nervous system (CNS) tissue in meat products with high sensitivity (Schönenbrücher, H., Adhikary, R., Mukherjee, P., Casey, T.A., Rasmussen, M.A., Maistrovich, F.D., Hamir, A.N., Kehrli, M.J., Richt, J., Petrich, J.W. [2008] J Agric Food Chem 56 , 6220–6226). We report that brain and spinal cord of mice provide fluorescence spectra similar to those of bovine brain and spinal cord. It is concluded that murine CNS tissue is an appropriate model system for bovine CNS tissue for the development of fluorometric CNS detection assays.