Synthesis and Characterization of Reactive End-Capped Poiymide Oligomers

A series of reactive, end-capped, polyimide oligomers has been prepared for possible use as planarizing coatings in the electronics industry. Thus, 1,3-bis(3-aminophenoxy)benzene was treated with various excess amounts of 2,2-bis(3,4-dicarboxyphenyl)hexafluoro-propane dianhydride in m-cresol containing toluene and isoquinoline. The resulting anhydride-terminated amic-acid oligomers were thermally imidized and then allowed to react with 3-aminophenylethyne, 1-phenyl-4-(3-aminophenyl)buta-1-ene-3-yne, 1-phenyl-4-(3-amino-phenyl)-1,3-butadiyne, 2-aminobiphenylene, or 1-phenyl-2-(3-amino-phenyl)ethyne. Thermal imidization of these intermediates produced the corresponding end-capped polyimide oligomers. The white oligomers were soluble in organic solvents, such as diglyme, and had glass transition temperatures (Tg's) between 95 and 145°C. The Tg of an ethynyl-terminated oligomer was reduced from 105 to 62°C upon the incorporation of 20 wt % of the reactive plasticizer bis[2-(3-ethynylphenoxy)ethyl]ether. The oligomers underwent exothermic polymerizations between 225 and 420°C. Their TGA thermograms showed 5% weight losses near 530°C in air.     

Measurement of 3-hydroxyisovaleric acid in urine from marginally biotin-deficient humans by UPLC-MS/MS

Measurement of 3-hydroxyisovaleric acid (3HIA) in human urine has been shown to be a useful indicator of biotin status for a variety of clinical situations, including pregnancy. The work described herein presents a novel UPLC-MS/MS method for accurate and precise quantitation of urinary 3HIA. This method utilizes sample preparation prior to quantitation that has been simplified compared to the previous GC-MS method. To demonstrate the suitability of the UPLC-MS/MS method for human bio-monitoring, this method was used to measure 3-HIA in 64 human urine samples from eight healthy adults in whom marginal biotin deficiency had been induced experimentally by egg white feeding. 3HIA was detected in all specimens; the mean concentration [±standard deviation (SD)] was 80.6 ± 51 μM prior to inducing biotin deficiency. Mean excretion rate for 3HIA (expressed per mol urinary creatinine) before beginning the biotin-deficient diet was 8.5 ± 3.2 mmol 3HIA per mol creatinine and the mean increased threefold with deficiency. These specimens had been previously analyzed by GC-MS; the two data sets showed strong linear relationship with a correlation coefficient of 0.97. These results provide evidence that this method is suitable for bio-monitoring of biotin status in larger populations.     

Synthesis of anisotropic nanoparticles by seeded emulsion polymerization

Anisotropic polystyrene nanoparticles of diameters below 0.5 microm were prepared by coating the surface of cross-linked polystyrene latex particles with a thin hydrophilic polymer layer prior to swelling the particles with styrene and then initiating second-stage free-radical polymerization. Conditions were found so that all particles had uniform asymmetry. The effect of surface chemistry on the development of particle anisotropy during seeded emulsion polymerization of sub-0.5 microm diameter particles was studied. The extent and uniformity of the anisotropy of the final particles depended strongly on the presence of the hydrophilic surface coating. Systematic variation of the degree of hydrophilicity of the surface coating provided qualitative insight into the mechanism responsible for anisotropy. Conditions were chosen so that the surface free energy favored the extrusion of a hydrophobic bulge of monomer on the hydrophilic surface of the particle during the swelling phase: the presence of a hydrophilic layer on the particle surface causes this asymmetry to be favored above uniform wetting of the particle surface by the monomer. Kinetic effects, arising from the finite time required for the seed to swell with the monomer, also play a role.     

Anomalous scaling in epitaxial growth on vicinal surfaces: meandering and mounding instabilities in a linear growth equation with spatiotemporally correlated noise

We have undertaken an extensive analytical and kinetic Monte Carlo study of the (2+1) dimensional discrete growth model on a vicinal surface. A non-local, phenomenological continuum equation describing surface growth in unstable systems with anomalous scaling is presented. The roughness produced by unstable growth is first studied considering various effects in surface diffusion processes (corresponding to temperature, flux, diffusion anisotropy). We found that the thermally activated roughness is well-described by a generalized Lai–Das Sarma–Villain model with non linear growth continuum equation and uncorrelated noise. The corresponding critical exponents are computed analytically for the first time and show a continuous variation in agreement with simulation results of a solid-on-solid model. However, the roughness related to the meandering instability is found, unexpectedly, to be well described by a linear continuum equation with spatiotemporally correlated noise.     

Ingested manganese chloride as a contrast agent for magnetic resonance imaging

Solutions of manganese chloride were force-fed to Sprague-Dawley rats. Magnetic resonance (MR) imaging was performed on (a) syringes containing different concentrations of manganese chloride, (b) rats after force feeding and (c) livers excised after sacrifice of the force-fed rats. Imaging was done with a 0.15-T resistive magnet. Multiple pulse sequences were used and T1 values were calculated. The signal intensity and T1 value obtained from a solution depended on the manganese concentration and the pulse sequence employed. At higher concentrations, no signal was produced due to extreme T2 shortening. Absorbed manganese affected the signal intensities and T1 values of the rats' livers. By appropriate selection of manganese concentration and pulse sequence, ingested manganese can serve as a combined gastrointestinal and hepatic MR contrast agent.     

Negative index and indefinite media waveguide couplers

We study the coupling interaction between dielectric waveguides and coupling elements made from negative-refracting media. The coupling configuration consists of a length of dielectric waveguide, which terminates either directly into or near a planar layer composed of the negative-refracting medium, and is followed by a second waveguide. Radiation output from the first waveguide is refocused at the position of the second waveguide, so that the negative-refracting layer serves as a coupler between the waveguides. Because both isotropic negative-index layers and bilayers of indefinite media can recover the near-field, evanescent components of a source field distribution, the coupling between the input and output waveguides can be highly efficient – in principle providing perfect, lossless coupling. We present simulations and some initial experimental results illustrating the coupling effect, and speculate on the potential for optical fiber couplers and integrated modulators. PACS 42.79.Gn; 41.20.-q; 42.70.-a     

A topological degree for orbits connecting critical points of autonomous systems

An argument based on topological degree is used to obtain an existence theorem for orbits connecting two critical points of an autonomous system. The result is applied to the existence of viscous profiles approximating shock waves in weak solutions of systems of nonlinear conservation laws. A result for the case where the Morse indices of the two critical points differ by more than one is also obtained.