Ethylenically unsaturated polyester resin composition

An ethylenically unsaturated polyester resin composition comprising (i) an ethylenically unsaturated polyester resin obtainable by reacting (i-a) at least one unsaturated dicarboxylic acid, or an ester or an anhydride thereof, wherein the unsaturated dicarboxylic acid comprises at least one ethylenically unsaturated dicarboxylic acid; and (i-b) at least one polyol; and (ii) a reactive diluent. The reactive diluent (ii) is an N vinyloxazolidinone of formula (I) in which R1, R2, R3 and R4 are independently from one another selected from a hydrogen atom and an organic moiety comprising 1 to 10 carbon atoms. The ethylenically unsaturated polyester resin (i) is characterized by a Hansen solubility parameter [delta]p of at least 5.5 MPa1/2. The ethylenically unsaturated polyester resin composition may be used for thermosets. N-vinyloxazolidinones of formula (I) are especially suitable for solubilizing ethylenically unsaturated polyester resins (i), and generally exhibit low toxicity and are virtually odorless.