An in-depth exploratory study on the mechanism of isocyanurate formation during the assembly of rigid PU/PIR polyurethane foams was performed thereby unravelling the role and working principle of the catalyst. Mimicking the complex pattern of the foam with mono-functional equivalents, the pathways to isocyanurate formation were investigated. Reactions focusing on potassium acetate as benchmark catalyst were thereto followed by in situ IR and NMR spectroscopy. Two pathways to isocyanurate formation from isocyanates were revealed: a one-component route via cyclotrimerization and a two-component route via carbamate and allophanate. We show that in the presence of alcohol and along with the formation of carbamate, isocyanurate is formed preferentially according to the two-component route in three consecutive steps. Allophanate, which in this study was isolated and characterized, is formed in situ in small transient concentrations from carbamate and the excess of isocyanate. For the first time it is proven that the allophanate intermediate undergoes an addition–elimination step with nucleophilic species to provide the isocyanurate.

中文翻译：

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硬质聚氨酯泡沫塑料组装过程中异氰脲酸酯的形成：基于原位IR和NMR光谱的机理研究†

对硬质PU / PIR聚氨酯泡沫塑料组装过程中异氰脲酸酯形成机理进行了深入的探索性研究，从而阐明了催化剂的作用和工作原理。模拟具有单官能当量的泡沫的复杂图案，研究了异氰脲酸酯形成的途径。进行集中于乙酸钾作为基准催化剂的反应，然后进行原位IR和NMR光谱。揭示了由异氰酸酯形成异氰脲酸酯的两种途径：通过环三聚作用的一组分途径和通过异氰酸酯形成的二组分途径。氨基甲酸酯和脲基甲酸酯。我们表明，在酒精的存在下，随着氨基甲酸酯的形成，异氰脲酸酯在两个连续的步骤中优先根据两组分途径形成。在本研究中分离和表征的脲基甲酸酯是由氨基甲酸酯和过量的异氰酸酯以较小的瞬时浓度原位形成的。首次证明，脲基甲酸酯中间体与亲核物质一起经历了加成-消除步骤，从而提供了异氰脲酸酯。