Resolution of Some Open Problems Concerning Multiple Zeta Evaluations of Arbitrary Depth

We prove some new evaluations for multiple polylogarithms of arbitrary depth. The simplest of our results is a multiple zeta evaluation one order of complexity beyond the well-known Broadhurst–Zagier formula. Other results we provide settle three of the remaining outstanding conjectures of Borwein, Bradley, and Broadhurst. A complete treatment of a certain arbitrary depth class of periodic alternating unit Euler sums is also given.     

Parity violation at neutron p-wave resonances of238U and232Th and related questions

Parity violation effects have been studied at 40 neutron p-wave resonances of the even-even nuclei²³⁸U and²³²Th. Of these 11 show parity violation effects larger than 2 standard deviations, making parity violation a rather common phenomenon. Parity mixing up to 10% has been found. The root-mean squared matrix elements for parity violation derived from these resonances are M=0.58 (+0.50/-0.25) meV for²³⁸U, respectively 1.39 (+0.35/-0.38) meV for²³²Th.     

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     

Oxygen inhibition in thiol–acrylate photopolymerizations

The overall effects of oxygen on thiol–acrylate photopolymerizations were characterized. Specially, the choice of thiol monomer chemistry, functionality, and concentration on the extent of oxygen inhibition were considered. As thiol concentration was increased, the degree of oxygen inhibition was greatly reduced because of chain transfer from the peroxy radical to the thiol. When comparing the copolymerization of 1,6‐hexanediol diacrylate with the alkane‐based thiol (1,6‐hexane dithiol) to the copolymerization with the propionate thiol (glycol dimercaptopropionate), it was found that the propionate system was much more reactive and polymerized to a greater extent in the presence of oxygen. In addition, the functionality was considered where the glycol dimercaptopropionate was compared to a tetrafunctional propionate of similar chemistry (pentaerythritol tetrakis(mercaptopropionate)). Given the same thiol concentration, the higher functionality thiol imparted a faster polymerization rate, due to the increased polymer system viscosity, which limited oxygen diffusion and decreased the extent of overall oxygen inhibition. Thus, preliminary insight is provided into how thiol monomer choice affects the extent of oxygen inhibition in thiol–acrylate photopolymerization. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 2007–2014, 2006     

Synthesis of a novel methacrylic monomer iniferter and its application in surface photografting on crosslinked polymer substrates

(Methacryloyl ethylenedioxycarbonyl) benzyl N,N‐diethyldithiocarbamate (HEMA‐E‐In) was synthesized and used as a monomer iniferter to develop a novel, photopatternable grafting technology. This molecule functions as both a methacrylic monomer and a photoiniferter (photoinitiator–transfer agent–terminator). The structure of HEMA‐E‐In was characterized by ¹H NMR, Fourier transform infrared, and ultraviolet–visible spectroscopies. In the presence of the monomer iniferter, methyl methacrylate was polymerized by exposure to 365‐nm ultraviolet radiation, confirming the initiation capability of HEMA‐E‐In. After the copolymerization of HEMA‐E‐In into a methacrylate‐based polymer, attenuated total reflectance Fourier transform infrared spectra revealed that the photoiniferter functionality was present at the surface of this polymeric substrate. Photografting of poly(ethylene glycol) monomethacrylate monomer from the surface caused a significant change in the hydrophobicity of the surface as demonstrated by contact angle measurements. The novel monomer photoiniferter HEMA‐E‐In initiates the polymerization of bulk monomer and provides a reactive functionality that facilitates further initiation and polymer modification by the polymerization of different monomers. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1885–1891, 2002     

Analysis of matrix nuclei spin flip satellite lines in EPR spectra: Application to trapped hydrogen atoms

The relative intensities and energy separation of allowed EPR lines of a paramagnetic species and partially forbidden spin flip satellite lines due to dipole-dipole coupling between the paramagnetic species and the matrix nuclei have been analyzed in a new way. The analysis allows one to determine both the distance to and the number of matrix nuclei that contribute to a given satellite transition. For hydrogen atoms trapped in a gamma-irradiated sulphuric acid glass at 77 K the analysis indicates that interaction occurs with four matrix protons at a distance of 2.15 Å. For trapped hydrogen atoms in phosphoric acid glass the analysis indicates interaction with four matrix protons at 2.37 Å.     

The nonaqueous,potentiometric titration of free hydrochloric acid in chloride-containing polymers

The thermal and/or catalytic degradation of chloride-containing polymers causes dehydrohalogenation which produces hydrochloric acid. A nonaqueous method has been developed for the termination of hydrochloric acid. The sample is dissolved in tetrahydrofuran and titrated potentiometrically with a standard tetrabutylammonium hydroxide solution in a 7.5% (V/V) aqueous tetrahydrofuran solution with a combination glass-calomel electrode. The method has a relative precision of ±3.7% at the 95% confidence limit and a sensitivity of 25 ppm HCI.     

Tributylgermanium hydride as a replacement for tributyltin hydride in radical reactions

Tributylgermanium hydride (Bu(3)GeH) can be used as an alternative to tributyltin hydride (Bu(3)SnH) as a radical generating reagent with a wide range of radical substrates. Tributylgermanium hydride has several practical advantages over tributyltin hydride, e.g. low toxicity, good stability and much easier work-up of reactions. The reagent can be easily prepared in good yield and stored indefinitely. Suitable substrates include iodides, bromides, activated chlorides, phenyl selenides, tert-nitroalkanes, thiocarbonylimidazolides and Barton esters. Alkyl, vinyl and aryl radicals can be generated in radical reactions including reduction and cyclisation processes. Common radical initiators such as ACCN and triethylborane can be used. The slower rate of hydrogen abstraction by carbon-centred radicals from Bu(3)GeH as compared to Bu(3)SnH facilitates improved cyclisation yields. Polarity reversal catalysis (PRC) with phenylthiol can be used in reactions which generate stable radical intermediates which will not abstract hydrogen from Bu(3)GeH.     

On-line storage and retrieval of chemical information. II. Substructure and biological activity searching

An improved interactive system for searching substructure and biological activity data has been developed. Features of the system include a two-level substructure search (fragment screen and atom by atom) and an expanded biological activity data base. The system operates on a file of about 150 000 compounds.