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首页> 外文期刊>RSC Advances >Forward and reverse reactions of N-methylaniline-blocked polyisocyanates: a clear step into double Arrhenius plots and equilibrium temperature of thermally reversible reactions
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Forward and reverse reactions of N-methylaniline-blocked polyisocyanates: a clear step into double Arrhenius plots and equilibrium temperature of thermally reversible reactions

机译： N -甲基苯胺封端的多异氰酸酯的正向和反向反应：迈向双Arrhenius图和热可逆反应平衡温度的清晰一步

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Blocked polyisocyanates are important building blocks mainly used in a variety of polyurethane coatings. In this study, the synthesis, kinetics of blocking and deblocking reactions and deblocking temperatures of a series of N-methylaniline-blocked polyisocyanates were studied in detail using a hot-stage FT-IR spectrophotometer adopting neat conditions. The results were compared with an aim to resolve the complex questions on the relationship between the forward and reverse reaction parameters. As a result, double Arrhenius plots for these thermally reversible reactions were proposed which paved the way for the prediction of equilibrium temperatures, i.e., the temperature at which both the forward and reverse reactions coexist. From these plots, the equilibrium temperature and the equilibrium rate constants for the forward and reverse reactions were determined. It was found that the electronic and steric effects of the substituents were reflected uniformly in the deblocking temperature, equilibrium temperature and rate constants of the reverse reactions. Among the six N-methylanilines studied, the one having a chloro substituent at a para position was found to be equally reactive compared to the unsubstituted N-methylaniline in the forward reaction and at the same time it was easily cleaved off in the reverse reaction. On the other hand the N-methylaniline possessing a methyl ester substituent at a para position was found to be slow in the forward reaction and cleaved off with highest rate in the reverse reaction. The data such as time required for 50% conversion into product and the equilibrium temperature in combination with deblocking temperature reported in this work will increase the prospects of these blocked polyisocyanates in the polyurethane industry.
机译：封端的多异氰酸酯是重要的结构单元，主要用于各种聚氨酯涂料中。在这项研究中，采用热条件的FT-IR分光光度计，研究了一系列 N -甲基苯胺嵌段的多异氰酸酯的合成，封闭和解封反应的动力学以及解封温度。比较结果，以解决关于正反反应参数之间关系的复杂问题。结果，提出了这些热可逆反应的双Arrhenius图，为预测平衡温度即（正向和反向反应共存的温度）铺平了道路。从这些曲线图中，确定了正向和反向反应的平衡温度和平衡速率常数。发现取代基的电子和空间效应在解封温度，平衡温度和逆反应的速率常数中被均匀地反映。在所研究的六种 N -甲基苯胺中，与未取代的 N 相比，在 para 位置具有氯取代基的苯胺具有相同的反应活性。 -甲基苯胺在正向反应中同时被逆向反应容易裂解。另一方面，发现在对位置具有甲基取代基的 N -甲基苯胺在正向反应中反应缓慢，在逆向反应中裂解率最高。 。这项工作中报告的数据，如50％转化为产品所需的时间，平衡温度以及解封温度，将增加这些嵌段聚异氰酸酯在聚氨酯工业中的应用前景。

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