Thiol–norbornene materials: Approaches to develop high Tg thiol–ene polymers

The ability to prepare high T_g low shrinkage thiol–ene materials is attractive for applications such as coatings and dental restoratives. However, thiol and nonacrylated vinyl materials typically consist of a flexible backbone, limiting the utility of these polymers. Hence, it is of importance to synthesize and investigate thiol and vinyl materials of varying backbone chemistry and stiffness. Here, we investigate the effect of backbone chemistry and functionality of norbornene resins on polymerization kinetics and glass transition temperature (T_g) for several thiol–norbornene materials. Results indicate that T_gs as high as 94 °C are achievable in thiol–norbornene resins of appropriately controlled chemistry. Furthermore, both the backbone chemistry and the norbornene moiety are important factors in the development of high T_g materials. In particular, as much as a 70 °C increase in T_g was observed in a norbornene–thiol specimen when compared with a sample prepared using allyl ether monomer of analogous backbone chemistry. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 5686–5696, 2007     

Fluid-fluid phase separation in colloid-polymer mixtures studied with small angle light scattering and light microscopy

Mixtures of colloidal silica spheres and polydimethylsiloxane in cyclohexane with a colloid-polymer size ratio of about one were found to phase separate into two fluid phases, one which is colloid-rich and one which is colloid-poor. In this work the phase separation kinetics of this fluid-fluid phase separation is studied for different compositions of the colloid-polymer mixtures, and at several degrees of supersaturation, with small angle light scattering and with light microscopy. The small angle light scattering curve exhibits a peak that grows in intensity and that shifts to smaller wave vector with time. The characteristic length scale that is obtained from the scattering peak is of the order of a few μm, in agreement with observations by light microscopy. The domain size increases with time as , which might be an indication of coarsening by diffusion and coalescence, like in the case of binary liquid mixtures and polymer blends. For sufficiently low degrees of supersaturation the angular scattering intensity curves satisfy dynamical scaling behavior.     

Compact Lie groups and factor spaces with respect to tori

Translated from Matematicheskie Zametki, Vol. 54, No. 7, pp. 124–135, July, 1993.     

Extension of multigrid methodology to supersonic/hypersonic 3-D viscous flows

A multigrid acceleration technique developed for solving the three-dimensional Navier–Stokes equations for subsonic/transonic flows has been extended to supersonic/hypersonic flows. An explicit multistage Runge–Kutta type of time-stepping scheme is used as the basic algorithm in conjunction with the multigrid scheme. Solutions have been obtained for a blunt conical frustum at Mach 6 to demonstrate the applicability of the multigrid scheme to high-speed flows. Computations have also been performed for a generic High-Speed Civil Transport configuration designed to cruise at Mach 3. These solutions demonstrate both the efficiency and accuracy of the present scheme for computing high-speed viscous flows over configurations of practical interest.     

TheA 1-and the ϕ-meson in QCD

Recently we used a method of stable analytic extrapolation to test whether strictly local duality between the asymptotic and the resonance region, which is believed to be valid in QCD, appears already at the present stage of QCD calculations. Probing the QCD ?-amplitude, we found a prominent bump structure in the resonance region, i.e. a rather direct evidence for the validity of local duality. In the present paper we confirm and extend this result by giving two further applications, theA ₁-meson and the ?-meson. While we do not meet theA ₁, as was to be expected since other sum rules can not separate it from the continuum, too, the extrapolation of the ?-amplitude leads to an enormous bump. Comparing this ?-bump with our ?-bump, we recover at least qualitatively the real proportions.     

Evaluation of atomic fluorescence, absorption and emission techniques for the determination of mercury

Summary Atomic fluorescence (AFS), absorption (AAS) and emission (AES) systems were evaluated for the determination of inorganic mercury. Identical vapour generation and amalgamation procedures were used to permit direct comparison of the performance of a commercial long-path AAS instrument to laboratory constructed non-dispersive AFS as well as He-MIP based AES instruments. Instrumental noise-limited detection limits (LOD) were 0.94, 2.4, 2.8 pg for AAS, AES and AFS techniques, respectively. Methodological LOD's were found to be blank controlled and similar for all three instruments, viz. 9, 25 and 16 pg for AAS, AFS and AES, respectively. All three systems produced accurate results at the low ng/l concentration, as verified by the analysis of a certified river water reference material (NRCC ORMS-1).     

Nuclear fusion in the mesic molecule d μ 3He

A new scheme is presented for the physical processes leading to the nuclear fusion reaction d(³He, ⁴He)p catalyzed by a negatively charged muon μ⁻. It is shown that the observable rate and yield of the nuclear reaction depend on a chain of ion-molecular reactions involving the participation of the dμ ³He molecule. New calculations of the nuclear fusion rates in the dμ³He molecule are presented. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 89–94 (25 January 1998) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Synthesis of 4H-pyrans by O-cyclization of 1,5-diketones

Substituted 4H-pyrans were obtained in high preparative yields by the reaction of 1,5-diketones with acetic anhydride and boron trifluoride etherate in diethyl ether. It is assumed that the heterocyclization of 1,5-diketones includes a step involving the formation and transformations of an acyloxy carbonium ion.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 3, pp. 320–322, March, 1992.