Abstract Irregular nanoscale micellar morphology was achieved by mixing an amphiphilic poly(ethylene oxide)‐ b ‐poly(propylene oxide)‐ b ‐poly(ethylene oxide) (PEO‐PPO‐PEO) triblock copolymer with an orthophthalic unsaturated polyester (UP) matrix. These systems were observed fully transparent. Modified matrices were filled with several multiwalled carbon nanotube (MWCNT) contents. Morphological analysis indicated a better dispersion of MWCNT with the use of a block copolymer when compared with a neat UP matrix/MWCNT composite, PEO‐PPO‐PEO acting like a surfactant. Furthermore, MWCNT did not affect the achievement of the irregular nanoscale micellar morphology. A reduction of mechanical properties of the composites with the block copolymer content was observed for UP/PEO‐PPO‐PEO composites without MWCNT. With the addition of MWCNT up to 0.5 wt% content, mechanical properties increased, decreasing again for 1 wt% MWCNT content probably due to the formation of agglomerates despite the use of the block copolymer as a surfactant. Flexural properties of composites decreased due to the incorporation of PEO‐PPO‐PEO copolymer, but significant higher levels of ductility were achieved. © 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E572–E581, 2013; View this article online at wileyonlinelibrary.com . DOI 10.1002/adv.21302