High-χ diblock copolymers containing poly(vinylpyridine-N-oxide) segments

Block copolymers exhibiting an enhanced segregation strength due to an underlying high Flory-Huggins interaction parameter (high χ) have attracted considerable attention because of their potential of forming microphase-separated domains with very small feature sizes (<10 nm) useful for next-generation lithography. Here, we report the synthesis, characterization, and self-assembly of poly(styrene)-block-poly(2-vinylpyridine N-oxide) (PS-b-P2VPNO) and poly(styrene)-block-poly(4-vinylpyridine N-oxide) (PS-b-P4VPNO) block copolymers. These PS-b-PVPNOs were obtained from the oxidation of their precursors, poly(styrene)-block-poly(2-vinylpyridine) (PS-b-P2VP) and poly(styrene)-block-poly(4-vinylpyridine) (PS-b-P4VP), respectively. The PS-b-PVPNOs exhibit an enhanced segregation as revealed by ordered cylindrical and lamellar structures in the sub-10 nm scale from copolymers with relatively low molecular weight. The morphologies and periodicities of the ordered structures were determined by small-angle X-ray scattering, while atomic-force microscopy was used to image the self-assembly in thin films. Estimates of the changes in disorder-order transition temperature and domain spacing are derived from a theory based on the effects of dipolar interactions. All the experimentally observed morphological changes resulting from the oxidation of P2VP and P4VP precursors can be qualitatively explained in terms of an increased dipole moment of vinylpyridine N-oxide segments. Our results demonstrate that PVPNO based block copolymers are versatile candidates toward nanopatterned structures with small feature sizes critical for the future microelectronics industry and beyond.