Catalytic Effects in Isocyanate Reactions

Abstract

Publisher Summary This chapter describes the catalytic effects in isocyanate reactions including polymerization of isocyanates, reactions of isocyanates with compounds containing active hydrogen, and their applications. Isocyanates react with compounds, which give a positive Zerewitinoff test. These include alcohols, water, phenols, amino groups (primary and secondary), carboxylic acids, and certain compounds having activated methylene groups, such as acetoacetic ester, and malonic ester. With water, the reaction product is a carbamic acid, which decomposes to form an amine and carbon dioxide, the latter being responsible for foam generation. One of the major fields of isocyanate catalysis is polymerization. Dimers are formed by aryl isocyanates at room temperature in the presence of certain amines or phosphines. Trimerization occurs in the presence of bases such as potassium acetate. Linear polymerization occurs at lower temperatures in polar solvents with an anionic catalyst, such as metallic sodium.