LIQUID-STATE SI-29 NMR-STUDY ON THE SOL-GEL REACTION-MECHANISMS OF ORMOSILS
LIQUID-STATE SI-29 NMR-STUDY ON THE SOL-GEL REACTION-MECHANISMS OF ORMOSILS
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DOI：
10.1016/0022-3093(93)91282-8
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发表时间：
1993-06-01
影响因子：
3.5
通讯作者：
MACKENZIE, JD
中科院分区：
文献类型：
--
作者：
IWAMOTO, T;MORITA, K;MACKENZIE, JD
用液态Si-29核磁共振波谱研究了有机改性硅酸盐(红壤)的溶胶-凝胶反应机理。用正硅酸乙酯(TEOS)、聚二甲基硅氧烷(PDMS)和水与异丙醇、四氢呋喃(THF)和盐酸(HCl)混合制备样品。用液态Si-29核磁共振波谱对几种不同反应时间的溶液进行了表征。从二甲基二乙氧基硅烷(DMDES)/正硅酸乙酯(TEOS)体系的溶液光谱中指认了一个新的中心D(Q)。通过水解的正硅酸乙酯与PDMS链中间的-O-Si(CH3)2-O-以及PDMS的硅醇端基HO-Si(CH3)2-O-反应，在反应过程中，PDMS与TEOS之间形成了键，PDMS链还以链(D)和/或环状D4四聚体(D4C)的形式存在。研究结果还显示了温度、酸和水对反应速率的预期影响。反应温度越高(室温至70℃)，PDMS与TEOS的共聚程度越高。水分含量(H2O/TEOS=2~4)对共聚反应速率影响不大，但显著提高了TEOS的缩聚速率。增加酸含量(HCl/TEOS=0.1~0.3)可提高TEOS的共聚和缩聚速率。提出了有机硅溶胶-凝胶反应机理的结构模型。
Sol-gel reaction mechanisms of organically modified silicates (ormosils) were conducted by liquid state Si-29 NMR (nuclear magnetic resonance) spectroscopy. Samples were prepared by mixing tetraethoxysilane (TEOS), polydimethylsiloxane (PDMS) and water with isopropanol, tetrahydrofuran (THF) and hydrochloric acid (HCl). Several series of solutions with different reaction times were examined by liquid state Si-29 NMR spectroscopy. A new proposed site, D(Q), was assigned from the spectrum of the solution of the dimethyldiethoxysilane (DMDES)/TEOS system. By the reaction between hydrolyzed TEOS and -O-Si(CH3)2-O- in the middle of PDMS chains as well as the silanol end groups, HO-Si(CH3)2-O-, of PDMS, bonds between PDMS and TEOS were formed and the PDMS chains were found to exist also as chains (D) and/or cyclic D4 tetramers (D4c) during the reaction. Results of this study also display the expected effects of temperature, acid and water on the reaction rates. The higher the reaction temperature (room temperature to 70-degrees-C), the more copolymerization between PDMS and TEOS occurs. The water content (H2O/TEOS = 2 to 4) had little effect on the rate of copolymerization but significantly increased the rate of condensation of TEOS. Increasing acid content (HCl/TEOS = 0.1 to 0.3) increased the rates of both copolymerization and condensation of TEOS. Structural models of the sol-gel reaction mechanisms of ORMOSILs are proposed.