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, including symmetric ripple, symmetric dimple, and asymmetric dimple A and dimple B phases have been predicted in theory. However, mixed brush phase separation with long-range order on planar substrates, especially in high-χ systems, has not been achieved experimentally in the melt due to synthetic challenges and a lack of knowledge about the distribution of the untethered chain ends. 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 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 to experimentally explore the phase diagram for high-χ mixed polymer brushes. Polystyrene (PS)/poly-2-vinylpyridine (P2VP) brushes were grown from an ultrathin, cross-linkable, mixed inimer coating. This coating leads to growth of mixed brushes with high grafting density, controllable molecular weights, and controllable grafting ratios. P2VP was grown by RAFT as the A component, and polystyrene was grown by NMP as the B component of the mixed brush. To explore the mixed brush phase diagram in the melt, we demonstrate that using thiol-ene chemistry to functionalize the high surface energy P2VP chains with a low surface energy group at the chain end leads to lateral phase separation. This chain-end modification equalizes the surface energy between the P2VP and PS brush components, bringing the P2VP chain-ends to the surface to prevent formation of the layered structure.

Effect of chain ends on the morphology of high-χ mixed polymer brushes

Fall 2022 abstracts, posters, and presentations will launch in mid-September.

ACS Fall 2022

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.