Brushes with multiple polymer types (A and B), known as mixed A/B brushes are a unique class of polymer brushes that can phase separate based on the interaction parameter (χ) between the A and B polymers and their lengths. Lateral phase separation with long-range order on planar substrates has not been achieved experimentally in melt due to synthetic challenges, and a lack of knowledge on the distribution of the untethered chain ends. Furthermore, in high-χ systems, there is a large mismatch in surface energy between the A and B components, leading to a layered structure instead of the lateral “rippled” phase separation that is desired for pattern transfer applications. In this work, mixed A/B polymer brushes with a high interaction parameter are grown from planar substrates using our previously developed inimer coating. The initiating sites in the coating for atom-transfer radical polymerization (ATRP) were switched to a reversible addition-fragmentation chain-transfer agent (RAFT-CTA) to expand the scope to include monomers that cannot be efficiently grown by ATRP, such as vinyl pyridines. RAFT polymerization also enables efficient chain-end functionalization. We utilized this RAFT switch methodology to grow P2VP with high grafting density as the A component of the mixed brush. Polystyrene was grown by NMP as the B component to create a high-χ P2VP/PS mixed brush with high grafting density, uniform grafting sites, and controlled chain length. In order to achieve lateral phase separation in the melt, we further demonstrate that using thiol-ene chemistry to functionalize the high surface energy P2VP chains with a low surface energy perfluorinated group at the chain end leads to lateral phase separation into a “rippled” structure. This chain-end modification equalizes the surface energy between the P2VP and PS brush components to prevent formation of the layered structure.

Lateral phase separation in high-χ mixed polymer brushes assisted by low surface energy chain-ends

ACS Spring 2022

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