Patent ID: 8609776

Claim:
An ethylenically unsaturated prepolymer having at least one end functional group X which is reactive by condensation, the end functional group X selected from the group consisting of hydroxyl and/or amine or free isocyanate reactive end functional groups with the absence of any ethylenic unsaturation end functional groups, said prepolymer having a number-average weight Mn (measured by GPC with polystyrene standards) ranging from 1000 to 5000, and an X number, expressed in mg KOH/g, ranging from 30 to 150, with said prepolymer being the reaction product of the following components A and B: A) a first component A comprising an ethylenically unsaturated resin carrying hydroxyl and/or amine reactive end functional groups, selected from 1) unsaturated polyesters having an OH number (measured on undiluted solid resin) of 70 to 170 mg KOH/g and an acid number (measured on resin in the undiluted solid state) of less than 10 mg KOH/g, said unsaturated polyesters being based on an acid component comprising at least maleic acid and/or anhydride with an aromatic acid and/or anhydride in a maleic/aromatic molar ratio ranging from 0.6/0.4 to 0.4/0.6, and 2) vinyl esters, said ethylenically unsaturated resin of component A) being diluted in at least one ethylenically unsaturated monomer which can copolymerize with the ethylenic unsaturation of said resin, and B) a second component B comprising a polyisocyanate with a functionality of 2 up to 3, and with the functionality of component A and/or B being greater than 2, and production of said prepolymers under conditions such that the proportions of A and B and the mean functionality of the reaction mixture A and B satisfy the Macosko-Miller relationship, in order to avoid any gelling by crosslinking, with, per functionality X chosen, the following conditions: for X=OH and/or amine, a ratio in equivalents r=NCO/(OH+NH 2 ) ranging from 0.01 to 0.6, and with said component B being added, gradually, to said component A, and for X=free NCO, with a ratio in equivalents r=NCO/(OH+NH 2 ) ranging from 1.2 to 3, and with said component A being added, gradually, to said component B wherein said vinyl esters are the reaction products of a diepoxy, an epoxy novolac or a cycloaliphatic or aliphatic diepoxy, with an ethylenically unsaturated monoacid.