Block copolymers with high Flory–Huggins interaction parameter (high χ) have attracted significant scientific interest due to their potential to phase separate into ultra-small nanophases (<10 nm) useful for next-generation lithography. Here, we report the synthesis, characterization, and phase separation behavior 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 prepared by the facile 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 show increased block immiscibility as revealed by ordered cylindrical and lamellar structures in the sub-10 nm scale from copolymers with low molecular weights. For several samples, the respective non-oxidized parent copolymers remained disordered. This highlights how a simple modification of common polymers such as P2VP and P4VP can lead to a strong increase in the dipole moment of the vinylpyridine N-oxide segments, and to an increased incompatibility with polystyrene. The morphologies and periodical dimensions of the well-ordered materials were determined by Small-Angle X-ray Scattering, while Atomic-Force Microscopy was used to image the self-assembly in the thin-film state. These results demonstrate how PVPNO-based block copolymers are versatile candidates for nanopatterned structures with very small feature sizes critical for the future microelectronics industry and beyond.

Rajeev Kumar

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