Methods of modifying block copolymers to enhance thermodynamic properties thereof without sacrificing material properties and methods of forming modified block copolymers having desired properties are disclosed. The modified block copolymers may be used, for example, as a mask for sublithographic patterning during various stages of semiconductor device fabrication. For example, block copolymers having desirable material properties, such as etch selectively, may be chemically modified to tailor a χ value thereof to optimize the process conditions for achieving a self-assembled state and to reduce a defectivity of the self-assembled block copolymer pattern.