Enhanced fracture toughness of epoxy resins with novel amine-terminated poly(arylene ether sulfone)–carboxylic-terminated butadiene-acrylonitrile–poly(arylene ether sulfone) triblock copolymers

Amine-terminated poly(arylene ether sulfone)–carboxylic-terminated butadiene-acrylonitrile–poly(arylene ether sulfone) (PES-CTBN-PES) triblock copolymers with controlled molecular weights of 15,000 (15K) or 20,000 (20K) g/mol were synthesized from amine-terminated PES oligomer and commercial CTBN rubber (CTBN 1300x13). The copolymers were utilized to modify a diglycidyl ether of bisphenol A epoxy resin by varying the loading from 5 to 40 wt %. The epoxy resins were cured with 4,4′-diaminodiphenylsulfone and subjected to tests for thermal properties, plane strain fracture toughness (K_IC), flexural properties, and solvent resistance measurements. The fracture surfaces were analyzed with SEM to elucidate the toughening mechanism. The properties of copolymer-toughened epoxy resins were compared to those of samples modified by PES/CTBN blends, PES oligomer, or CTBN. The PES-CTBN-PES copolymer (20K) showed a K_IC of 2.33 MPa m^0.5 at 40 wt % loading while maintaining good flexural properties and chemical resistance. However, the epoxy resin modified with a CTBN/8K PES blend (2:1) exhibited lower K_IC (1.82 MPa m^0.5), lower flexural properties, and poorer thermal properties and solvent resistance compared to the 20K PES-CTBN-PES copolymer-toughened samples. The high fracture toughness with the PES-CTBN-PES copolymer is believed to be due to the ductile fracture of the continuous PES-rich phases, as well as the cavitation of the rubber-rich phases. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 1556–1565, 2002; DOI 10.1002/app.10390