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991.
Bernhard Seidl Kadiriye Kalinyaprak‐Icten Norbert Fuß Michael Hoefer Robert Liska 《Journal of polymer science. Part A, Polymer chemistry》2008,46(1):289-301
In continuation of our research on new chromophores for photoinitiators (PIs) we investigated a series of double and triple bond containing PIs based on benzophenone (BP), thioxanthone, benzil (BZ), benzildimethylketal (BDK), and hydroxyalkylphenone. UV‐Vis spectroscopy revealed an absorption shifted up to 50 nm to the visible range of the spectrum. With steady state photolysis experiments, the rates of decomposition (Rd) were determined. Compared to the commercially available reference PIs the Rd of the new PIs were nearly identical. By quenching reactions with 2,2,6,6‐tetramethylpiperidine‐1‐oxyl (TEMPO), α‐cleavage was identified for Type I initiators. Generally, all new compounds are suitable as PI especially for longer wavelengths. Nevertheless it has to be noted that the PI concentration has to be selected carefully to achieve optimum reactivity. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 289–301, 2008 相似文献
992.
Ludk Toman Miroslav Janata Jií Spv
ek Petr Vl
ek Petra Ltalov Bohumil Masa Antonín Sikora 《Journal of polymer science. Part A, Polymer chemistry》2004,42(23):6098-6108
ABCBA‐type pentablock copolymers of methyl methacrylate (MMA), styrene (S), and isobutylene (IB) were prepared by a three‐step synthesis, which included atom transfer radical polymerization (ATRP) and cationic polymerization: (1) poly(methyl methacrylate) (PMMA) with terminal chlorine atoms was prepared by ATRP initiated with an aromatic difunctional initiator bearing two trichloromethyl groups under CuCl/2,2′‐bipyridine catalysis; (2) PMMA with the same catalyst was used for ATRP of styrene, which produced a poly(S‐b‐MMA‐b‐S) triblock copolymer; and (3) IB was polymerized cationically in the presence of the aforementioned triblock copolymer and BCl3, and this produced a poly(IB‐b‐S‐b‐MMA‐b‐S‐b‐IB) pentablock copolymer. The reaction temperature, varied from ?78 to ?25 °C, significantly affected the IB content in the product; the highest was obtained at ?25 °C. The formation of a pentablock copolymer with a narrow molecular weight distribution provided direct evidence of the presence of active chlorine at the ends of the poly(S‐b‐MMA‐b‐S) triblock copolymer, capable of the initiation of the cationic polymerization of IB in the presence of BCl3. A differential scanning calorimetry trace of the pentablock copolymer (20.1 mol % IB) showed the glass‐transition temperatures of three segregated domains, that is, polyisobutylene (?87.4 °C), polystyrene (95.6 °C), and PMMA (103.7 °C) blocks. One glass‐transition temperature (104.5 °C) was observed for the aforementioned triblock copolymer. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 6098–6108, 2004 相似文献
993.
Miroslav Ploščica 《Algebra Universalis》2005,54(3):323-335
We introduce the Local Separation Property (LSP) for distributive semilattices. We show that LSP holds in many semilattices
of the form Conc A, where A is a lattice. On the other hand, we construct an abstract example of a distributive lattice without LSP. Our research is
connected with the well known open problem whether every distributive algebraic lattice is isomorphic to the congruence lattice
of some lattice.
Received December 10, 2004; accepted in final form June 6, 2005. 相似文献
994.
Vladimí ra Novotn V ra Hamplov Miroslav Ka par Milada Glogarov Karel Kní ek Siegmar Diele Gerhard Pelzl Chris Jones David Coleman Noel A. Clark 《Liquid crystals》2005,32(8):967-975
New mesogens composed of achiral bent molecules with thermally stable ester linkages, and laterally substituted by a methoxy group symmetrically near the central benzene ring, were synthesized. Texture, calorimetric, electro-optical, X-ray and dielectric measurements were performed. In most of studied compounds the antiferroelectric B2 phase was found on cooling from the isotropic phase, followed by the B7 phase at lower temperatures. Undulation of layers in the B7 phase was confirmed by precise synchrotron studies. 相似文献
995.
KateŘina Krijtová Miroslav štĚpánek Karel Procházka Stephen E. Webber 《Journal of fluorescence》1998,8(1):21-25
Properties of the interfacial region between the nonpolar core and the polar shell in polystyreneblock-poly (methacrylic acid) micelles were studied by fluorescence techniques using 5-(N-octadecanoyl) aminofluorescein (OAF) as a probe for microfluidity and local pH. The block copolymer used was tagged between
blocks by one 9, 10-diphenylanthracene (DPA) group, which allowed us to study binding of OAF at the interface by means of
nonradiative energy transfer between DPA and OAF. A shift in the pK
a of OAF and appreciable changes in anisotropy and quenching efficiency due to immobilization of the fluorophore head-group
in hydrophobic poly(methacrylic acid) domains were observed after binding of the probe at the interface. 相似文献
996.
997.
In the present paper we study some properties of positive quasi-orders on simigroups and using these results we describe all
semilattice and chain homomorphic images of a semigroup.
Supported by Grant 0401B of RFNS through Math. Inst. SANU. 相似文献
998.
Robert Liska 《Journal of polymer science. Part A, Polymer chemistry》2004,42(9):2285-2301
Several benzophenone‐ and thioxanthone‐based photosensitizers (PSs) were covalently bonded to hydroxyalkylphenone‐ and aminoalkylphenone‐based photoinitiators (PIs) to enhance the rate of the excitation‐transfer effect due to the close vicinity of the PS to the PI. The properties of these new systems were investigated with UV spectroscopy and photo‐differential scanning calorimetry. Broadband irradiation experiments and selective excitation of the PS were carried out for the physical mixtures and covalently bonded PI/PS combinations to investigate the effect of excitation transfer. Selective excitation of the PS chromophore revealed that the energy transfer was significantly increased in covalently bonded initiators in comparison with the physical mixtures. This effect was most pronounced for the hydroxyalkylphenones that were sensitized by suitable benzophenone derivatives, especially at low PI concentrations. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 2285–2301, 2004 相似文献
999.
1000.