Block copolymers of unsaturated polyester were prepared by cocondensation polymerization of hydroxyl-or carboxyl-terminated liquid rubbers or polyethylene glycols in the presence of maleic anhydride, phthalic anhydride, and propylene glycol. The resultant unsaturated polyesters were then diluted with styrene monomer and cured by using peroxide and heat. The mechanical properties of the cured block copolymers were determined and compared with those of a control resin or a corresponding toughened physical blend. In addition, the sheet-molding compounds made with these polyesters were obtained and investigated. (1-3). Chemical mod ifications by introducing either long-chain glycols (e.g., diethylene, dipropylene, or triethylene glycol) or long-chain saturated dibasic acids (e.g., adipic acid or sebacic acid) are common practice. However, a significant amount of such long-chain substances is needed to impart a sufficient im provement in toughness. This requirement, in turn, results in a large sacrifice of other mechanical properties.
IMPROVEMENT OF THE FRACTURE TOUGHNESS and impact resistance of rigid unsaturated polyester has played an important role in the development of high-performance polymeric composites. Unsaturated polyesters can be modified by numerous chemical and physical methodsAmong physical modifications, the use of dispersed elastomers for en hancement of toughness in unsaturated polyester resins and molding ma terials has frequently been reported (4-17). These elastomers include both solid and liquid rubbers.