The invention concerns a method for catalytic (cyclo)condensation of monomer isocyanates, characterised in that it comprises: a) reacting starting monomer isocyanates with a catalyst comprising a mineral or organic salt of a compound of formula (I), wherein Y^- is selected among: a negatively charged oxygen atom, and a carbonaceous radical comprising a negative charge borne by an atom of column VB of the periodic table or by an oxygen atom advantageously by a nitrogen atom and whereof the bond with the silicon of formula (I) is borne by an atom of column VB of the periodic table, advantageously by a nitrogen atom; wherein R₁, R₂ and R₃, identical or different, represent a monovalent hydrocarbon radical having advantageously 1 to 30 carbon atoms, or a precursor of said compound, at a temperature of at least 20 C. and advantageously of at least 40 C. and not more than 200 C., advantageously not more than 150 C.; b) stopping the (cyclo)condensation reaction at the desired transformation rate; and c) optionally eliminating unreacted monomers or the reaction with other reactive compounds with the isocyanate function. ##STR1##