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The analysis for the hydroxyl (OH) group is one of the most important functional group analyses fir silicones. Hydroxyl functionality may be present as silanol (sioh) water (HOH) and possibly as carbinol (coh) or carboxyl (cooh) amine groups on silicon substituents may also be a source of active hydrogen The silanol group is particularly important in silicone chemistry because it is through this function that condensation polymeriz-ation occurs to produce silicones it is also an active catalyst for siloxane bond rearrangement water is a condensation by-product so the concentra-tion of water in silicones is directly related to the amount of silanol and silane condensation the chemical or instrumental analysis for silanol and water in silicones is complicated by several factors First the fact that silanol and water generally occur together requires silanol and water-specific analyses Unfortunately there are few if any silanol-specific chemical analyses Most chemical analyses are nonspecific methods for total active hydrogen thus silanol and water and other active hydrogens including carbinols and carboxyl are determined in total Second the reactivity of the silanol group can vary widely depending on the molecular structure or environment Third concentrations of interest range from low parts per million to percent levels. The most common methods for the chemical analysis of silanol and water in silicones are disussed below Additional information on less common methods is available in the first edition of this book the analysis of functional groups such as carbinol or carboxyl less commonly found in silicones can be accomplished with some of the procedures described below Much more information is available in texts on general organic functional group analysis |
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a79003625: 金币+50, 翻译EPI+1, ★★★★★最佳答案 2013-02-08 19:18:58
a79003625: 金币+50, 翻译EPI+1, ★★★★★最佳答案 2013-02-08 19:18:58
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在对硅酮的官能团分析中，对羟基自由基的分析是最重要的部分之一。羟基可能以硅醇键（Si-OH）、水(H-OH)、碳醇键（C-OH）或羧基（COOH）的形式存在。与硅取代基相连的氨基也可能是活性氢的一个来源。硅醇基在硅酮化学中尤为重要，因为硅酮正是通过硅醇基的缩聚反应合成的。硅醇基同时还是一种硅氧烷键重排反应的有效催化剂。水是缩聚反应的副产物，它在硅酮中的浓度与参与缩聚反应的硅醇和硅烷的量直接相关。针对硅酮中硅醇和水的化学分析及仪器分析是非常复杂的，这是由于以下几点原因。首先，硅醇和水一般是相伴存在的，这要求对它们进行特异性地分析。然而不幸的是，对硅醇的特异性化学分析方法，即便存在的话，也是极少的。大多数化学分析方法都是针对总活性氢的非特异性方法，因此它们只能测定硅醇、水及其它活性氢（如碳醇键和羧基）的总量。其次，根据硅醇基的分子结构或所处环境，其反应性可能显著不同。第三，所需检测的浓度范围较宽，下至几ppm，上至百分之几。 针对硅酮中硅醇和水的最常用的化学分析手段将在下面讨论，其它不常用的方法在本书第一版中有记载。对于硅酮中不太常见的官能团（如碳醇键或羧基）的分析，下文所述的步骤中也有记载。更多的信息可以参阅关于综合有机官能团分析的内容。 |
2楼2013-02-08 16:16:11
