Asymmetric block copolymer based on regioregular poly(3-hexyl thiophene) (P3HT) and poly(ethylene oxide) (PEO) was synthesized through Heck reactions. The addition of PEO block has no influence in the effective conjugation length of P3HT block and apparently provides colloidal stability for the formation of stable nanostructures. Introduction of poor solvent to good solvent containing P3HT-b-PEO will induce the crystallization-driven assembly of the P3HT into cylindrical micelles with a P3HT core, owing to π–π stacking of the conjugated backbone of P3HT. The absorption spectra of the cylindrical micelles reveal a red shift as compared to the polymer in good solvent, indicating the extension of conjugation length with an improved π–π stacking of the polymer chains within the cylindrical micelles. Our results indicated that cylindrical micelles with varied diameter and length can be obtained when solvent properties were varied using several different binary solvent mixtures. More interestingly, we demonstrate that ultrasonic processing can fragment the cylindrical micelles only when the ratio of poor solvent increases. This provides a facile and effective way to fabricate cylindrical micelles for applications in the area of polymer solar cell as well as organic optoelectronics device. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014, 131, 41186.