To enable future applications of block copolymer assemblies, it is critical to develop simple approaches to achieve ultrasmall domain spacings from readily available polymers. In this report, we demonstrate that reduction of polymethyl(meth)acrylate-containing block copolymers with LiAlH4 provides novel poly(hydroxyisobutylene)/poly(methallyl alcohol) and poly(hydroxypropylene)/poly(allyl alcohol))-based block copolymers that after thermal annealing display significantly enhanced microphase separation. The effective chi values for these polymers were found to be >= 0.3, and d-spacing values as small as 6.5-7.2 nm were obtained for various morphologies. This work establishes a simple and universal strategy for generation of high chi block copolymers from readily available precursors.