Synthesis of Y-Shaped Polymer Brushes on Silica Particles and Hierarchical Surface Structures Fabricated by the Coassembly Approach

Coassembly of polymer brushes and linear polymers in selective solvents provides a unique method for the fabrication of surface nanostructures on solids. However, some fundamental problems, including the effect of architecture of polymer brushes on the surface coassembly and the thermal dynamic process of the assembly, are left unsolved. To solve the fundamental problems, in this research we synthesized Y-shaped polymer brushes on silica particles and studied the coassembly mechanism of the Y-shaped polymer brushes and linear block copolymers (BCPs). Poly(ethylene glycol)-block-polystyrene (PEG-b-PS) with a pyridyl disulfide group at the junction point (PEG-(SS-py)-PS) was synthesized by a combination of click chemistry, thiol-disulfide exchange reaction, and reversible addition-fragmentation chain transfer polymerization. The block copolymer and the precursors were characterized with H-1 NMR, C-13 NMR, size exclusion chromatography, and matrix-assisted laser desorption ionization time-of-flight mass spectrometry. PEG-(SS-py)-PS chains were anchored to the thiol-modified silica particles by the thiol-disulfide exchange reaction, and Y-shaped polymer brushes with PEG and PS arms were prepared on silica particles (PEG/PS-SiO2). Coassemblies of PEG/PS Y-shaped polymer brushes and linear PEG-b-PS BCPs with different PS block lengths were studied. In THE/methanol mixtures (1/7, by volume), BCP chains and PEG/PS brushes can coassemble into surface structures. The PS block length and BCP concentration play key roles in the fabrication of surface structures. With an increase in PS block length, fewer BCP chains are organized onto the surfaces of silica particles due to the limited surface area. Different morphologies were observed in the coassembly of Y-shaped polymer brushes and linear BCPs. In the coassembly of PEG/PS-SiO2 and PEG-b-PS89, only spherical micelles are formed on silica particles. At high BCP concentrations, Y-shaped polymer brushes and PEG-b-PS143 chains coassemble into surface wormlike structures on silica particles. In the coassembly of PEG/PS-SiO2 and PEG-b-PS306, layered surface structures and fused vesicles are formed on silica particles. This research paves a new approach to the fabrication of hierarchical nanostructures on solid surfaces.