Hindered lithium dialkylamide initiators for the living anionic polymerization of methacrylic esters

Lithium diisopropylamide is an efficient initiator for the anionic polymerization of methyl methacrylate in polar solvents at –78°C. Predictable molecular weights based on the initiator concentration were obtained, yields were quantitative, and molecular weight distributions were relatively narrow (<1.30). The presence of an amino end group and confirmation of the initiation mechanism were confirmed by potentiometric titration using HClO₄. Number-average molecular weights determined by titration agreed well with values determined by SEC. Other lithium dialkylamides that contain larger alkyl groups such as lithium diisobutylamide were less efficient initiators. This was attributed to the more nucleophilic anion due to less steric hindrance near the nitrogen atom. Molecular weight distributions were significantly broadened (>2.0), and molecular weight control was not achieved. However, polymer yields were quantitative. In all cases, PMMA stereochemistry was indicative of a solvent-separated lithium counterion, and triad compositions were identical to organolithium initiated homopolymers, i.e., 78% syndiotactic, 20% heterotactic, and 2% isotactic. © 1994 John Wiley & Sons, Inc.     

Dammann光栅在光互连中的应用

本文将Ｄａｍｍａｎｎ光栅［１，２］应用于光互连，提出了用Ｄａｍｍａｎｎ光栅实现完全混洗的方法．一个２×２的Ｄａｍｍａｎｎ光栅与一个成像透镜的组合，具有与四焦点透镜类似的成像作用．像面上，像的位置与Ｄａｍｍａｎｎ光栅的位置有关，适当选择光栅的位置可以实现不同元素数目及不同元素密度的完全混洗．本文给出了有关的理论推导及实验结果．     

Synthesis of perfluoroalkyl-containing steroidal glycosides

A new kind of fluorine-containing amphiphiles -- perfluoroalkyl-containing steroidal glycos-ides were synthesized in good yield through perfluoroalkylation by means of sodium dithionite-initiatedaddition of R_FI to olefinic system. Preliminary study showed that these glycosides could formvesicles in aqueous medium as observed by electron microscopy.     

A new approach to c-glycoside congeners: Metal carbene mediated methylenation of aldonolactones.

Versatile intermediates for the synthesis of C-glycosides and oxygen heterocycles are readily available through titanium mediated methylenation of aldonolactones.Aldonolactones may be alkylated using the titanium carbene complex 2. The resulting enol ethers are of value as potential substrates for glycosidase enzymes. A high yield two step process for alkylation of these enol ethers was described. The products and procedures are relevant to the synthesis of mycotoxins, including citreoviridin and aurovertin B.     

薄层色谱法分离烷基芳基酮肟立体异构体

我们对酮肟中间体及肟醚类拟除虫菊酯进行了分析。经核磁共振证明,酮肟中间体在生成肟醚南反应过程中其立体构型木发生变化。目前分离酮肟立体异构物的工作报道较少。我们通过薄层色谱对不同取代的具有活性的几种酮肟异构体的分离进行了探讨。 1 实验部分     

关于Freedman和Waltman一个定理的注记

本文指出了文献[1]中的主要定理的错误,给出了两个反例,并且给出了一个改进的定理。     

Nuclear magnetic resonance of oriented molecules in lyotropic liquid crystalline media: p-cresol

Proton-proton distance ratios and order parameters for partially oriented p-cresol in a lyotropic mesophase derived from potassium laurate are obtained. The order parameters are the largest yet found for an ordered solute in a nematic-like lyotropic system. The dipolar couplings and structural data were independent of the rotational potential from 0–200 cal mol^?1.     

A Mössbauer study on the surface hyperfine field of uniform hematite particles

A Mössbauer spectroscopic study was performed on uniform spherical hematite particles (99±9 nm, Sample I) and those enriched with⁵⁷Fe on the surface (Sample II). A striking difference was found between the spectra of these two samples, in that Sample I showed a spectrum with nearly symmetrical resonant absorption lines, while Sample II showed a spectrum with the lines broadened toward the central peaks asymmetrically. But after the⁵⁷Fe-enriched sample was heated to 623 K, the spectral lines became narrower due to the diffusion of the surface⁵⁷Fe-ions into the bulk. The above results showed that the centripetal broadening of the spectral lines for small uniform hematite particles resulted from a surface effect. The surface exhibited a hyperfine field about 5.2% lower than that for the bulk. The wider distribution of the surface hyperfine field was explained by structural inhomogeneity of the surface.