Fluorescence recovery after photobleaching measurements of polymers in a surface forces apparatus

The surface forces apparatus has been combined with fluorescence recovery after photobleaching to measure translational diffusion of polymer confined between mica sheets. This article presents findings using polydimethylsiloxane with number‐average molecular weight M_n = 2200 g mol^?1, the chains end‐labeled with soluble fluorescent dye. Melts with thickness 10 nm display a translational diffusion coefficient (D) with a bulk component and a slower component assigned to surface diffusion. Reduction of thickness to 1.8 nm causes mobility to split into two populations—an immobile fraction (immobile on the time scale of 30–60 min) and a mobile fraction who's D slow only weakly with diminishing film thickness. However, when load causes the confining mica sheets to flatten, D of the mobile fraction drops by up to an additional order of magnitude, depending on the local pressure that squeezes on the polymer. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2010     

Reactions of naphthalene in N2O5?NO3?NO2? air mixtures

The reactions of naphthalene in N₂O₅? NO₃? NO₂? N₂? O₂ reactant mixtures have been investigated over the temperature range 272–297 K at ca. 745 torr total pressure and at 272 K and ca. 65 torr total pressure using long pathlength Fourier transform infrared absorption spectroscopy. 2,3-Dimethyl-2-butene was added to the reactant mixtures at 272 K to rapidly scavenge the NO₃ radicals both initially present in the added N₂O₅ and formed from the thermal decomposition of N₂O₅ during the reactions. The data obtained in the presence and absence of added 2,3-dimethyl-2-butene showed that napthalene undergoes initial reaction with the NO₃ radical to form an NO₃-naphthalene adduct, which either rapidly decomposes back to the reactants (at a rate of ca. 5 × 10⁵ s^?1 at 298 K) or reacts exclusively with NO₂ to form products. When NO₃ radicals, N₂O₅ and NO₂ are in equilibrium, this overall process is kinetically equivalent to reaction of naphthalene with N₂O₅, and previous kinetic and product studies have indeed assumed the reactions of naphthalene and alkyl-substituted naphthalenes in N₂O₅? NO₃? NO₂? air mixtures to be with N₂O₅, and not with NO₃ radicals.     

Hydro­gen bonding in 2-(hydroxy­methyl)-1,3-propane­diol and N,N′-bis­[2-hydroxy-1,1-bis­(hydroxy­methyl)­ethyl]­malon­amide

The mol­ecule of 2-(hydroxy­methyl)-1,3-propane­diol, C₄H₁₀O₃, lies across a mirror plane in space group P2₁/m, with disorder of both terminal hydroxyl H atoms. The molecules are linked by three O—H⋯O hydrogen bonds which combine to form sheets; in each O—H⋯O bond, the H atom resonates between the two O atoms. In the crystal structure of N,N′-­bis­[2-hydroxy-1,1-bis­(hydroxy­methyl)­ethyl]­malon­amide, C₁₁H₂₂N₂O₈, the molecule lies about a twofold axis and has four strong hydrogen bonds which form a mixture of chains and dimers; these combine to give a three-dimensional supramolecular framework.     

Polymer-bound osmium oxide catalysts

Polymer-supported oxidic osmium catalysts based on cross-linked poly(4-vinyl pyridine) were synthesized by various routes and characterized by a number of physical techniques (Raman, IR, XPS, ¹³C and ¹⁵N solid-state NMR spectroscopy). Model compounds of type Os₂O₆L₄ (L = pyridine, 4-iso-propyl pyridine, and 4-tert-butyl pyridine) were obtained under the conditions of the catalyst synthesis. The catalytic systems were successful in the dihydroxylation of alkenes.     

Synthesis of 3-vinylpiperidine

A novel synthesis of 3-vinylpiperidine from commercially available ethyl 3-pyridylacetate is described.     

Free Vibration Analysis of Rotating Nonlinearly Elastic Structures with Symmetry: An Efficient Group-Equivariance Approach

A study is made of the dynamics of oscillating systems with a slowly varying parameter. A slowly varying forcing periodically crosses a critical value corresponding to a pitchfork bifurcation. The instantaneous phase portrait exhibits a centre when the forcing does not exceed the critical value, and a saddle and two centres with an associated double homoclinic loop separatrix beyond this value. The aim of this study is to construct a Poincaré map in order to describe the dynamics of the system as it repeatedly crosses the bifurcation point. For that purpose averaging methods and asymptotic matching techniques connecting local solutions are applied. Given the initial state and the values of the parameters the properties of the Poincaré map can be studied. Both sensitive dependence on initial conditions and (quasi) periodicity are observed. Moreover, Lyapunov exponents are computed. The asymptotic expressions for the Poincaré map are compared with numerical solutions of the full system that includes small damping.