Semi-conducting two-dimensional (2D) nanoobjects, prepared by self-assembly of conjugated polymers, are promising materials for optoelectronic applications. However, there has been no example of 2D nanosheets with controlled lengths and aspect ratios at the same time via self-assembly. Herein, the inventors successfully prepared uniform semi-conducting 2D sheets using a conjugated poly(cyclopentenylene vinylene) homopolymer and its block copolymer by blending and heating. Using these as 2D seeds, living crystallization-driven self-assembly (CDSA) was achieved by adding the homopolymer as a unimer. Interestingly, unlike typical 2D CDSA examples showing radial growth, this homopolymer assembled only in one direction. Owing to this uniaxial growth, the lengths of the 2D nanosheets could be precisely tuned with narrow dispersity according to the unimer-to-seed ratio. The inventors also studied the growth kinetics of the living 2D CDSA and confirmed first-order kinetics. Subsequently, the inventors prepared several 2D block comicelles (BCMs), including penta-BCMs in a one-shot method.