Method for the preparation of low-viscosity (poly) isocyanates

Process for the preparation of a low-viscosity polyfunctional isocyanate composition containing at least one isocyanate trimer containing an isocyanurate and/or biuret unit and at least one isocyanate dimer containing a uretidinedione unit, from starting isocyanate monomers, and optionally from other monomers, this process comprising the following steps:

• i) the starting reaction medium is heated, in the absence of dim rization catalyst, to a temperature of at least 50° C., advantageously of at least 80° C., preferably of at least 120° C., and of not more than 200° C., advantageously of not more than 170° C., for a period of less than 24 hours, advantageously of less than 5 hours;
• ii) the reaction mixture from step i) containing unreacted monomers is reacted with a (cyclo)trimerization or (cyclo)condensation catalyst, under (cyclo)trimerization or (cyclo)condensation conditions;
• iii) the unreacted starting monomers are removed from the reaction mixture from step ii);
• iv) the low-viscosity polyfunctional isocyanate composition comprising at least one isocyanate trimer and at least one isocyanate dimer is isolated.

Process for the preparation of a low-viscosity polyfunctional isocyanate composition containing at least one isocyanate trimer containing an isocyanurate and/or biuret unit and at least one isocyanate dimer containing a uretidinedidne unit, from starting isocyanate monomers, and optionally from other monomers, this process comprising the following steps:

• i) the starting monomers are reacted with a (cyclo) trimerization or (cyclo) condensation catalyst under (cyclo)trimerization or (cyclo)condensation conditions;
• ii) the reaction mixture from step i) containing unreacted isocyanate monomers is heated, in the absence of dimerization catalyst, to a temperature of at least 50° C., advantageously of at least 80° C., preferably of at least 120° C., and of not more than 200° C., advantageously of not more than 170° C., for a period of less than 24 hours, advantageously of less than 5 hours;
• iii) the unreacted starting monomers are removed from the reaction mixture from step ii);
• iv) the low-viscosity polyfunctional isocyanate composition comprising at least one isocyanate trimer and at least one isocyanate dimer is isolated.

Process for the preparation of a low-viscosity polyfunctional isocyanate composition comprising at least one isocyanate dimer containing a uretidinedione unit and at least one other compound having a function derived from the isocyanate function, starting with isocyanate monomers and another compound comprising at least one function other than isocyanate, which is reactive with the isocyanate function, this process comprising the following steps:

• i) the starting reaction medium is heated, in the absence of dimerization catalyst, to a temperature of greater than at least 80° C., advantageously at least 120° C., preferably at least 130° C., and less than at least 200° C., advantageously at least 170° C., for a period of less than 24 hours, advantageously less than 5 hours;
• ii) the reaction product from step i) containing unreacted isocyanate monomers and a compound comprising at least one function other than the isocyanate function, which is reactive with the isocyanate function, are reacted together, optionally in the presence of a catalyst;
• iii) the isocyanate monomers and, where appropriate, the compound comprising at least one function other than the isocyanate function, which is reactive with the isocyanate function, are removed from the reaction product from step ii);
• iv) the polyfunctional isocyanate composition of low-viscosity comprising at least one isocyanate dimer containing a uretidinedione unit and at least one other function derived from the isocyanate function, is isolated.

Process for the preparation of a low-viscosity polyisocyanate composition comprising at least one isocyanate dimer containing a uretidinedione unit and at least one other compound containing a function derived from the isocyanate function, starting with isocyanate monomers and with another compound comprising at least one function other than isocyanate, which is reactive with the isocyanate function, this process comprising the following steps:

• i) an isocyanate monomer is reacted with a compound comprising at least one function other than an isocyanate function, which is reactive with the isocyanate function, optionally in the presence of a catalyst;
• ii) the reaction mixture from step i) containing unreacted isocyanate monomers is heated, in the absence of dimerization catalyst, to a temperature of greater than at least 80° C., advantageously at least 120° C., preferably at least 130° C. and not more than 200° C., advantageously not more than 170° C., for a period of less than 24 hours, advantageously less than 5 hours;
• iii) the monomers and, where appropriate, the compound comprising at least one function other than the isocyanate function, which is reactive with the isocyanate function, are removed from the reaction mixture from step ii);
• iv) the low-viscosity polyisocyanate composition comprising at least one polyisocyanate trimer and at least one polyisocyanate dimer is isolated.

Process according to any one of the preceding claims, characterized in that, for the dimerization of the starting monomers, a compound of general formula I:

• in which
• R is a mono- or n-valent hydrocarbon-based group having from 1 to 30 carbon atoms, in which the hydrocarbon-based chain can be interrupted by one or more chalcogen atoms and can bear 1 to 3 OH groups, and n is an integer ranging from 1 to 3,
• and/or products derived from this derivative by a reaction with a compound bearing an aliphatic isocyanate function,
• is added to the reaction medium containing the starting monomers.

Use of a compound of general formula I:

• in which
• R is a mono- or n-valent hydrocarbon-based group having from 1 to 30 carbon atoms, in which the hydrocarbon-based chain can be interrupted by one or more chalcogen atoms and can bear 1 to 3 OH groups, and n is an integer ranging from 1 to 3,
• and/or products derived from this derivative by reaction with a compound bearing an aliphatic isocyanate function,
• for the preparation of isocyanate dimers from aliphatic isocyanate monomers, with a degree of conversion of at least 5%, preferably at least 10%, of the starting isocyanate functions into uretidinedione functions.