Toughening of epoxy resins modified with polyetherester block copolymers: The influence of modifier molecular architecture on mechanical properties

Thermoplastic elastomers based on polyetheresters with polyoxytetramethylen e soft segments and poly(hexamethyleneterephthalate) hard segments were use d to toughen anhydride-cured epoxy resins. The ratio between hard and soft segments and the crystallinity of the hard segments prepared by incorporati ng poly(hexamethyleneisophthalate) in the block copolymer were varied in or der to examine the effect of the modifier's molecular architecture on morph ology and mechanical properties of the resin, such as toughness, strength, and stiffness. The experimental data show that segmented polyetheresters ar e suitable toughening agents for epoxies. The compatibility between resin a nd toughener and also the mechanical properties of the modified resin depen d on the ratio between the hard and soft segments. Epoxy resins blended wit h 10 wt % of the polyetherester exhibit an increase in toughness by 50-150% , while strength and modulus decrease by 20% or less. An optimal phase adhe sion at levels between 70 and 85 wt % of soft segments in the modifier resu lts in a maximum of toughness enhancement (by about 150%)of the resin accom panied with only a slight drop in strength and stiffness (by about 15%). Th e glass transition temperature is only slightly affected. (C) 2000 John Wil ey & Sons, Inc. J Appl Polym Sci 76: 623-634, 2000.