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. (c) 2012 Wiley Periodicals, Inc. Adv Polym Techn 32: E572E581, 2013; View this article online at wileyonlinelibrary.com. DOI 10.1002/adv.21302