Abstract: The invention relates to a process for the preparation of polyurethanes by reacting polyisocyanates a) with compounds having at least two hydrogen atoms reactive with isocyanate groups b), wherein a polyisocyanate a) used is at least one polyisocyanate ai) having an average functionality of greater than 2, a content of diisocyanates of not more than 2% by weight and a content of uretonimines of not more than 4% by weight, based in each case on the weight of the polyisocyanate ai).

Abstract: The invention relates to polyphenylenepolymethylene polyisocyanates (B) comprising (B1) the 2-ring product of polyphenylenepolymethylene polyisocyanate (B2) the 3-ring product of polyphenylenepolymethylene polyisocyanate (B3) the 4-ring product of polyphenylenepolymethylene polyisocyanate (B4) the 5-ring product of polyphenylenepolymethylene polyisocyanate, wherein the constituents (B2), (B3) and (B4) are, at a content of (B1) of up to 55% by weight, based on the weight of (B), present in a weight ratio of (B2):(B3):(B4) of 8±4:3.5±1.8:1.2±0.9 and the component (B) comprises at least 85% by weight, based on the weight of the component (B), of the constituents (B1), (B2), (B3) and (B4).

Abstract: The invention relates to a process for the preparation of polyurethanes by reacting polyisocyanates a) with compounds having at least two hydrogen atoms reactive with isocyanate groups b), wherein a polyisocyanate a) used is at least one polyisocyanate ai) having an average functionality of greater than 2, a content of diisocyanates of not more than 2% by weight and a content of uretonimines of not more than 4% by weight, based in each case on the weight of the polyisocyanate ai).

Abstract: The invention relates to a process for preparing prepolymers containing isocyanate groups by reacting a) diisocyanates with b) compounds having at least two hydrogen atoms which are reactive toward isocyanate groups in the presence of c) catalysts, and subsequently separating off the excess monomeric diisocyanates, wherein the diisocyanates a) used are unsymmetrical diisocyanates and the catalysts c) used are organometallic catalysts and these organometallic catalysts are removed, blocked or deactivated before the monomeric diisocyanates are separated off.

Abstract: A process for the preparation of isocyanates from carbamic esters.

Abstract: In a process for the preparation of isocyanates from carbamic esters, (i) a mixture containing a monofunctional or polyfunctional carbamic ester is passed continuously into a cleavage reactor or a cascade of two or more cleavage reactors, (ii) the carbamic ester is subjected to a thermal cleavage to give isocyanate and alcohol, (iii) the cleavage gas escaping from the cleavage reactor or reactors and containing the isocyanate, the alcohol, any uncleaved and/or partly cleaved carbamic ester and byproducts is brought into contact with a liquid coolant and condensing agent, cooled and at least partly condensed and (iv) the isocyanate and the alcohol are obtained from the cooled cleavage gas and the condensate in a rectification column, a part-stream of the alcohol obtained being used as liquid coolant and condensing agent for cooling and condensing the cleavage gas.

Abstract: Highly functional aromatic polyisocyanates are prepared by reacting aromatic polyisocyanates, if required as a mixture with further mono- and/or polyisocyanates, with addition of catalytic acidic substances and water, by a process wherein the aromatic polyisocyanates used comprise at least one tolylene diisocyanate and the catalytic acidic substance used is at least one alkyl and/or aralkyl phosphate, and the process is carried out in such a way that the water is added with a temperature/time gradient increase from 5 to 60°/hour and until an isocyanate modification of the starting NCO terminal groups from 1 to 80% is established.