Department of Chemical and Materials Engineering, University of Kentucky, Lexington, KY 40506-0046, USA.
J Colloid Interface Sci. 2011 Oct 15;362(2):345-53. doi: 10.1016/j.jcis.2011.06.064. Epub 2011 Jul 5.
While organically bridged alkoxysilane precursors such as bis(triethoxysilyl)ethane (BTESE) find increasing use in materials synthesis, their polymerization still has not been subject to detailed kinetic investigations. One factor complicating the measurement and interpretation of the behavior of these monomers is their tendency to aggregate during polymerization into small clusters or particles. Here, the phase behavior and kinetics of BTESE during polymerization in acidic water-ethanol solutions are investigated in situ using (29)Si NMR spectroscopy. Based on macroscopic observation of the colloidal stability of the reacting solutions, a ternary pseudo-phase diagram is constructed and solutions that seem from a macroscopic point of view to be favorable for kinetic investigation are probed in situ using (29)Si NMR. However, even when the solutions remain optically clear, the polymerization mixtures are sometimes prone to gradual loss of NMR signal. The rate of signal loss is found to be dependent on the initial composition as well as the pH of the reacting mixtures. We speculate that this phenomenon is caused by microphase separation of reaction intermediates formed early in the polymerization process. This phenomenon is likely to affect the formation and distribution of oligomers in the solution that eventually react together to form a material.
虽然有机桥联烷氧基硅烷前体，如双（三乙氧基硅基）乙烷（BTESE），在材料合成中得到越来越多的应用，但它们的聚合仍然没有经过详细的动力学研究。在测量和解释这些单体的行为时，一个复杂的因素是它们在聚合过程中倾向于聚集形成小的簇或颗粒。在这里，使用（29）Si NMR 光谱原位研究了酸性水-乙醇溶液中 BTESE 聚合过程中的相行为和动力学。基于对反应溶液胶体稳定性的宏观观察，构建了一个三元拟相图，并使用（29）Si NMR 原位探测了从宏观角度来看有利于动力学研究的溶液。然而，即使溶液仍然保持光学透明，聚合混合物有时也容易逐渐失去 NMR 信号。发现信号损失的速率取决于初始组成以及反应混合物的 pH 值。我们推测这种现象是由聚合过程早期形成的反应中间体的微相分离引起的。这种现象可能会影响最终一起反应形成材料的溶液中低聚物的形成和分布。
