Summary: A low‐molar‐mass poly(acrylic acid) with a narrow molar‐mass distribution, prepared by SG1 nitroxide‐mediated controlled free‐radical polymerization, was subjected to end‐group analysis to confirm its living nature. 1H and 31P NMR spectroscopy confirmed the presence of the SG1‐based alkoxyamine end group. Furthermore, chain extension with styrene and n‐butyl acrylate demonstrated the ability of the homopolymer to initiate the polymerization of a second block. These results open the door to the synthesis of poly(acrylic acid)‐based block copolymers by direct nitroxide‐mediated polymerization of acrylic acid.
Acrylic acid polymerization using an alkoxyamine initiator based on SG1 (N‐tert‐butyl‐N‐(1‐diethyl phosphono‐2,2‐dimethylpropyl) nitroxide resulting in a homopolymer capable of initiating the polymerization of a second block. 相似文献
The one-loop branching ratios for the process are calculated in the general two Higgs doublet model (Model II), taking into account existing constraints on the model parameters.
For Higgs boson masses below 50 GeV and of the fraction of such Z decays are at the level of , but can be significantly stronger for very low or high , where the dependence of these results on other model parameters like and the mass of the charged Higgs boson is found to be of little importance. The results are compared to the LEP measurements,
which are sensitive to branching ratios of of the order for masses GeV, but approach for low masses. By relating the expectation to the experimental limits, constraints on the parameter space of the 2HDM are
derived.
Received: 28 November 1998 / Published online: 27 April 1999 相似文献
. In this paper, we identify the limiting stress tensor of a thin elastic shell whose thickness approaches zero. In the linear
case, we use a convergence result established for the displacement field in order to get the convergence of the contravariant
components of the linearised stress tensor. In the nonlinear case, the identification of the first Piola‐Kirchhoff stress
tensor is made through a formal asymptotic analysis. In both cases, we show that these limiting stress fields depend on the
geometry of the shell and on the boundary conditions.
(Accepted June 1, 1998) 相似文献
The use of non-homopolymerizable monomers such as 1,1-diphenylethylene (DPE) in the synthesis of functional polymers and block copolymers by cationic polymerization has been recently reported. The most important parameters in this process, the kinetics and extent of ionization and capping as well as the stability of the cation, were investigated by studying the reaction with TiCl4 of 1-methoxy-1,1-diphenyl-3,3,5,5-tetramethylhexane, a model for DPE-capped polyisobutene chain-end. This study was performed using 1H NMR and the high-purity stopped-flow device coupled with UV-visible spectroscopy. 相似文献
The pH-dependent self-condensation of the [Mo 2 S 2 O 2 ] 2+ complex fragment gives the wheellike Mo12 cluster depicted on the right (ball-and-stick model; large balls: S, medium balls: O, small balls: Mo). Applying this synthetic strategy to other starting materials could provide access to other polyoxothiometalates with well-defined cavities. 相似文献
The conversion of trichloromethane in mixtures with air was investigated under normal pressure in a gliding discharge (GD)
reactor operated in both a homogeneous gas system and with a solid catalyst. The Pt catalyst supported by a honey-comb cordierite
structure was placed in the reactor below the ends of the electrodes. Cl2 and HCl were the main products of the CHCl3 conversion. The presence of CCl4 was also noted. The influence of the electrode length and the distance between the electrodes in the narrowest section on
CHCl3 conversion was examined. The Pt catalyst revealed some activity in the trichloromethane processing. This resulted in an increased
overall CHCl3 conversion with the portion of CHCl3 converted to CCl4 smaller than that in the homogeneous system. The effect of temperature on CHCl3 conversion was found to be significant. 相似文献
This article reports on the ion permeability of self-assembled monolayers (SAMs) formed on the surface of charged alkanethiol-protected gold nanoparticles, so-called monolayer-protected clusters (MPCs). The capacitance and thus the charging energy required to add/remove an electron from the metal core are extremely sensitive to ions entering the monolayer, and the extent of ion penetration can be tuned by the charge and size of the ions and the permittivity of the solvent. Experimentally, this effect is comparable to ion association with conventional redox molecules, indicating that MPCs despite their large size and the fundamentally differing nature of the electron transfer process can be treated analogously to redox molecules. 相似文献