This article reports on the modification of unsaturated polyesters by poly (ethylene glycol) end groups in order to influence the solution behavior in styrene and to modify mechanical properties of the cured resin. The synthesis was done by the reaction of a carboxyl-terminated unsaturated polyester with various poly(ethylene glycol) mono-methyl ethers of molecular weights from 350 to 2000 g/mol. The characterization and curing properties of the synthesized block copolymers are presented. The glass transition temperatures decrease with increasing length of the poly(ethylene glycol) end groups. The introduction of long poly(ethylene glycol) end groups (2000 g/mol) leads to a phase separated and partly crystalline block copolymer with a melting point of 48 degrees C. The block copolymers can be easily diluted in styrene to create the curable resins. The mixtures containing the block copolymers with the short poly(ethylene glycol) end groups (350 and 550 g/mol) could be cured in a reasonably short time. Compared to commercial unsaturated polyesters the mechanical testing revealed that the tensile strength is decreasing while the elongation is increasing.