聚苯乙烯-铂络合物对不饱和化合物硅氢加成反应的催化活性

合成了聚苯乙烯－铂络合物,研究了它对不同类型不饱和化合物与甲基一氯硅烷及甲基氢二乙氧基硅烷硅氢加成反应的催化特性。结果表明,其催化活性和选择性受不饱和化合物的电子效应和空间位阻效应以及硅氯化试剂结构等多种因素的影响。聚苯乙烯－铂络合物对连有一个取代基的苯乙烯、丙烯酸甲酯与 氯硅烷及甲基氢二乙氧基硅 硅氢加成反应具有很高的催化活性,对连有两个取代基的甲基丙烯酸甲酯无催化活性;该催化剂可选择性催化烯丙     

Polar silicones: structure-dielectric properties relationship

A series of polar silicones was synthesized in order to compare their dielectric properties. Different substituents with high dipole moment (epoxy, pyridyl, aldehyde, cyano-, nitroazobenzene) were attached by hydrosilylation to a poly(dimethyl-methylhydro)siloxane. Thiol-ene addition on a dimethyl-methylvinyl siloxane copolymer with similar composition was also used for chemical modifications with chloro- or carboxy- derivatives. This approach allowed comparison of properties with emphasis on dielectric behavior measured in liquid state, as a preliminary step in design and preparation of materials suitable for dielectric elastomers. Although a relatively low content of polar groups was used (8%), permittivity values of 5.4 and even 7.4 were achieved (at 10 kHz), either due to the large dipole moment or to the presence of important amounts of moisture. The water sorption capacity of the polar silicones was investigated by dynamic vapor sorption, while structural parameters of model molecules were calculated, in order to correlate the dielectric properties with the polarity/hydrophilicity of the substituents to the silicone chain. A combined effect of the calculated dipole moment, molar polarizability, molar volume, and the measured water sorption capacity on dielectric permittivity was observed.     

Synthesis and characterization of siloxane‐based cyanate ester elastomers from readily available materials: a top‐down approach

A number of siloxane‐based cyanate ester (SiCE) elastomers were prepared from commercially available starting reagents employing a hydrosilylation reaction. Each elastomer was designed to utilize 2,4,6‐tris(allyloxy)‐1,3,5‐triazine as a crosslinker and multifunctional vinyl component in the hydrosilylation reaction, ensuring that the triazine rings were completely formed, and thus the elastomers resemble fully cured cyanate ester networks. The hydride‐terminated siloxane components used were varied from small‐molecule siloxanes to pre‐polymers of different molecular weights. Attenuated total reflectance Fourier transform infrared analysis confirmed the successful hydrosilylation reaction and complete curing of the SiCE elastomers via functional group analysis. Thermal characterization by thermogravimetric analysis and differential scanning calorimetry demonstrated that thermal properties of the elastomers could be tailored depending on the type of siloxane component that was utilized. The gel content of the elastomers was also determined. Investigations into the effects of a platinum catalyst on the elastomers determined that the presence of the catalyst affected the thermochemical stability of the SiCE elastomers. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.     

Evaluating the Effects of Carbon Nanoreactor Diameter and Internal Structure on the Pathways of the Catalytic Hydrosilylation Reaction

Three different types of carbon nanoreactors, double‐walled nanotubes (DWNT), multi‐walled nanotubes (MWNT) and graphitised carbon nanofibers (GNF) have been appraised for the first time as containers for the reactions of phenylacetylene hydrosilylation catalysed by a confined molecular catalyst [Rh₄(CO)₁₂]. Interactions of [Rh₄(CO)₁₂] with carbon nanoreactors determining the ratio of β‐addition products are unchanged for all nanoreactors and are virtually unaffected by the confinement of [Rh₄(CO)₁₂] inside carbon nanostructures. Conversely, the relative concentrations of reactants affecting the ratio of addition and dehydrogenative silylation products is very sensitive to nanoscale confinement, with all nanoreactors demonstrating significant effects on the distribution of reaction products as compared to control experiments with the catalyst in bulk solution or adsorbed on the outer surface of nanoreactors. Surprisingly, the widest nanoreactors (GNF) change the reaction pathway most significantly, which is attributed to the graphitic step‐edges inside GNF providing effective anchoring points for the catalyst and creating local environments with greatly altered concentrations of reactants as compared to bulk solution. Possessing diameters significantly wider than molecules, GNF impose no restrictions on the transfer of reactants while providing the strongest confinement effects for the reaction. Furthermore, GNF facilitate the effective recyclability of the catalyst and thus represents a superior nanoreactor system to carbon nanotubes.     

利用湿化学法对不同粒径硅粉进行表面改性研究

通过湿化学方法,利用硅氢化反应,通过对刻蚀体系、脱氧方式、刻蚀后硅粒子的分离方法等工艺的优化,成功地实现了微米硅、纳米硅及硅量子点的表面烃基改性。傅里叶变换红外光谱及扫描电子显微镜测试结果表明,硅粒子的表面是通过Si—C键的连接方式实现了烃基改性。与改性前相比,改性后的硅粒子具有显著提升的抗氧化性和抗团簇能力,能够在有机溶剂中形成稳定的分散体系。值得一提的是,与未经改性的硅量子点相比,经烃基改性后的硅量子点的荧光发射性能有了大幅提高,有望应用于光电领域。     

甲氧基聚氧化乙烯丙基三甲氧基硅烷的合成与表征

以甲氧基聚氧化乙烯单烯丙基醚和三甲氧基硅烷为原料进行硅氢加成反应,实验分别从反应时间、温度、催化剂用量、反应物物质的量比、甲氧基聚氧化乙烯单烯丙基醚分子量对甲氧基聚氧化乙烯单烯丙基醚的硅氢加成反应转化率的影响进行了研究。结果表明,当甲氧基聚氧化乙烯单烯丙基醚与三甲氧基硅烷的物质的量比为1∶1.2,反应温度85℃,时间8...     

3-氯丙基三甲氧基硅烷合成新方法的研究

为提高产率、降低成本,以3-氯丙烯和三甲氧基硅烷为原料、水合三氯化钌为催化剂进行3-氯丙基三甲氧基硅烷的一步合成反应,研究了反应温度、催化剂浓度、原料的加料方式、反应时间、原料的配比对产物收率的影响.结果表明,最佳的反应条件为反应温度80℃、钌催化剂质量分数63 μg/g、3-氯丙烯向三甲氧基硅烷中滴加方式、三甲氧基硅...     

加成型硅橡胶用含酯基有机硅增粘剂的制备及应用性能

以含氢硅油（PHMS）和1,6-己二醇二丙烯酸酯（HDDA）为原料,通过硅氢加成反应合成了含酯基的有机硅增粘剂（PHMS-g—HDDA）,并将其用于加成型液体硅橡胶（LSR）。采用傅立叶变换红外光谱（FT—IR）及核磁共振波谱（1HNMR）对PHMS—g—HDDA的结构进行了表征;研究了PHMS-g-HDDA用量对LSR的黏度、力学性能、硫化特性及与聚碳酸酯、对苯二甲酸乙二醇酯及热塑性聚氨酯粘接性能的影响。结果表明,PHMS—g—HDDA可显著提高LSR的粘接性能,且对LSR的黏度、力学性能和硫化特性有明显影响。当PHMS—g—HDDA用量为0．9份时,硅橡胶的综合性能较为理想。此时硅橡胶的拉伸强度为5．3MPa、拉断伸长率为380％、撕裂强度为14．7kN／m、邵尔A硬度为47．6度;焦烧时间及正硫化时间最小,分别为51S和68S;与各种基材的粘接性良好。     

Cobalt Carbonyl‐Based Catalyst for Hydrosilylation of Carboxamides

The cobalt carbonyl [Co₂(CO)₈] complex is employed as a useful catalyst for the reduction of tertiary amides to the corresponding tertiary amines using 1,1,3,3‐tetramethyldisiloxane (TMDS) and poly(methylhydrosiloxane) (PMHS) as silane reagents under thermal (100 °C) or photo‐assisted conditions (UV, 350 nm at room temperature). Of particular interest, a low catalytic amount (0.5 mol%) of [Co₂(CO)₈] is used to perform the reaction with 2.2 equiv. of PMHS at 100 °C for 3 h. This reaction is the first example of a cobalt‐catalyzed hydrosilylation of amides.

     

Efficient and Selective Hydrosilylation of Carbonyl Compounds Catalyzed by Iron Acetate and N‐Hydroxyethylimidazolium Salts

Aromatic aldehydes, along with aryl alkyl, heteroaryl alkyl, and dialkyl ketones were efficiently reduced to their corresponding primary and secondary alcohols, respectively, in high yields, using the commercially available and inexpensive polymeric silane, polymethylhydrosiloxane (PMHS), as reducing agent. The reaction is catalyzed by in situ generated iron complexes containing hydroxyethyl‐functionalized NHC ligands. Turnover frequencies up to 600 h⁻¹ were obtained.