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a79003625木蟲(chóng) (著名寫(xiě)手)
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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: 金幣+50, 翻譯EPI+1, ★★★★★最佳答案 2013-02-08 19:18:58
a79003625: 金幣+50, 翻譯EPI+1, ★★★★★最佳答案 2013-02-08 19:18:58
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在對(duì)硅酮的官能團(tuán)分析中，對(duì)羥基自由基的分析是最重要的部分之一。羥基可能以硅醇鍵（Si-OH）、水(H-OH)、碳醇鍵（C-OH）或羧基（COOH）的形式存在。與硅取代基相連的氨基也可能是活性氫的一個(gè)來(lái)源。硅醇基在硅酮化學(xué)中尤為重要，因?yàn)楣柰峭ㄟ^(guò)硅醇基的縮聚反應(yīng)合成的。硅醇基同時(shí)還是一種硅氧烷鍵重排反應(yīng)的有效催化劑。水是縮聚反應(yīng)的副產(chǎn)物，它在硅酮中的濃度與參與縮聚反應(yīng)的硅醇和硅烷的量直接相關(guān)。針對(duì)硅酮中硅醇和水的化學(xué)分析及儀器分析是非常復(fù)雜的，這是由于以下幾點(diǎn)原因。首先，硅醇和水一般是相伴存在的，這要求對(duì)它們進(jìn)行特異性地分析。然而不幸的是，對(duì)硅醇的特異性化學(xué)分析方法，即便存在的話，也是極少的。大多數(shù)化學(xué)分析方法都是針對(duì)總活性氫的非特異性方法，因此它們只能測(cè)定硅醇、水及其它活性氫（如碳醇鍵和羧基）的總量。其次，根據(jù)硅醇基的分子結(jié)構(gòu)或所處環(huán)境，其反應(yīng)性可能顯著不同。第三，所需檢測(cè)的濃度范圍較寬，下至幾ppm，上至百分之幾。 針對(duì)硅酮中硅醇和水的最常用的化學(xué)分析手段將在下面討論，其它不常用的方法在本書(shū)第一版中有記載。對(duì)于硅酮中不太常見(jiàn)的官能團(tuán)（如碳醇鍵或羧基）的分析，下文所述的步驟中也有記載。更多的信息可以參閱關(guān)于綜合有機(jī)官能團(tuán)分析的內(nèi)容。 |
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