Abstract: The invention relates to a method for producing a polyurethane prepolymer with an isocyanate termination, having a low content of free diisocyanates. The invention also relates to a method for producing polyurethanes, polyurethane urea or thermoplastic polyurethane granules.

Abstract: The invention concerns a thermosetting elastomer composition based on modified polycyanurate with improved thermal resistance obtainable by a polymerization method in the presence of a catalyst (D) of a mixture comprising at least: (A) a cyanate, (B) a block copolymer consisting of: a) at least a central block (B1) non-miscible with the cyanate and sufficiently long to provide the composition with elastomeric character; and b) at least two terminal blocks (B2) located on each side of the central block and comprising groups reactive with the cyanate, each of the blocks (B2) being sufficiently long to be miscible with the cyanate; and (C) a mineral filler reactive with the cyanate, in proportions such that the ratio r is not less than 5, but remains less than a threshold value to avoid phase inversion, said method comprising steps which consist in: I) mixing (A), (B), (C) and (D) until a homogeneous mixture is obtained at a temperature higher than the melting point of (A) and of (B) but lower than about 130° C.