Atmospheric Degradation of Volatile Methyl-Silicon Compounds
摘要:
The current widespread use of poly(dimethylsiloxane)s (PDMS) in a broad range of applications leads to their release into soil environments where they degrade to monomeric products, primarily dimethylsilanediol, most of which enter the atmosphere by volatilization. The major degradation pathway of volatile organosilicon compounds in the atmosphere is expected to be a reaction with hydroxyl (OH) radicals. In this work, the kinetics of the gas-phase reactions of dimethylsilanediol, trimethylsilanol, and tetramethylsilane with the OH radical were measured using a relative rate method which employed the N2H4 + O-3 reaction as a nonphotolytic source of OH radicals, with analysis by Fourier transform infrared (FT-IR) spectroscopy in a 5870 L chamber. The measured values of the OH radical reaction rate constants (cm(3) molecule(-1) s(-1)) at 298 +/- 2 K are as follows: dimethylsilanediol, (8.1 +/- 1.0) x 10(-13); trimethylsilanol, (7.2 +/- 0.8) x 10(-13); and tetramethylsilane, (8.5 +/- 0.9) x 10(-13). These values lead to an estimate of tropospheric lifetimes with respect to reaction with the OH radical of ca. 15 days for these organosilicon compounds. FT-IR spectroscopy and atmospheric pressure ionization mass spectrometry (API-MS) were employed to analyze the products of OH radical- and Cl atom-initiated photooxidations of dimethylsilanediol and trimethylsilanol. Infrared signatures of the probable formate ester intermediate products from both silanols were detected. API-MS analyses indicated the formation of methylsilanetriol from dimethylsilanediol, of both dimethylsilanediol and methylsilanetriol from trimethylsilanol, and of the corresponding intermediate formate esters. Possible reaction mechanisms are discussed.
Silanol Compound, Composition, and Method for Producing Silanol Compound
申请人:NATIONAL INSTITUTE OF ADVANCED INDUSTRIAL SCIENCE AND TECHNOLOGY
公开号:US20170183363A1
公开(公告)日:2017-06-29
The purpose of the present invention is to provide silanol compounds that can be used as raw materials of siloxane compounds and the like, and a composition of the silanol compounds, as well as to provide a production method that makes it possible to produce silanol compounds at excellent yield. A composition comprising 5 mass % to 100 mass % of a silanol compound represented by Formulas (A) to (C) can be prepared by devising to produce silanol compounds under water-free conditions, to produce silanol compounds in a solvent having the effect of suppressing the condensation of silanol compounds, and to perform other such processes, the composition being able to be used as a raw material or the like of siloxane compounds because the silanol compounds can be stably present in the resulting composition.
bear SiH and SiOR2 groups on the same siliconatom, R13Si–O–SiR32−n(OR2)nH (n = 0, 1, or 2), via a simple catalyst- and additive-free dealcoholization reaction between silanols and alkoxyhydrosilanes has been developed. These alkoxyhydrosiloxanes can be easily converted into Si(OR2)3-containing siloxanes by zinc catalyzed alkoxylation and alkoxy-containing silphenylene polymers by platinum catalyzed
condensation of the mixed systems of tetraethoxysilane (TEOS) and dimethyldiethoxysilane (DDS) dissolved in methanol. With ammonia catalysis, the hydrolysis reaction orders for TEOS and DDS in the mixed systems remained first order, which is similar to that observed for their corresponding single silane component precursorsystems. The hydrolysis rate constant for TEOS in the mixed systems was larger than that
原位 29Si 液态核磁共振 (NMR) 用于研究四乙氧基硅烷 (TEOS) 和二甲基二乙氧基硅烷 (DDS) 溶解在甲醇中的混合体系的氨催化水解和缩合。在氨催化下,混合体系中 TEOS 和 DDS 的水解反应顺序仍为一级,这与在它们相应的单一硅烷组分前体系统中观察到的类似。TEOS 在混合体系中的水解速率常数大于 TEOS 在单一硅烷组分前体体系中的水解速率常数。同时,混合前驱体体系中DDS的水解速率常数小于单一硅烷组分前驱体体系中DDS的水解速率常数。水解和缩合动力学表明 TEOS 和 DDS 之间的水解-缩合相对速率更相容,这显着影响了所得二氧化硅颗粒的最终微观结构。小角 X 射线散射 (SAXS) 实验显示颗粒网络中具有典型的双分形结构。