A combined computer simulation and experimental study on coassembly of poly­(2-(dimethylamino)­ethyl methacrylate)-block-polystyrene (PDMAEMA-b-PS) block copolymers and PS brushes on silica particles was performed. PS brushes on silica particles at two different grafting densities were prepared by the “grafting to” approach, and PDMAEMA-b-PS block copolymers with different molecular weights and compositions were synthesized by reversible addition–fragmentation chain transfer polymerization. In THF/methanol mixtures, block copolymer chains and PS brushes coassemble into surface micelles (s-micelles), with collapsed PS cores and PDMAEMA coronae. Meanwhile, block copolymer chains are able to self-assemble into block copolymer micelles (b-micelles). Computer simulation results and experimental results indicate that block copolymer concentration, PS and PDMAEMA block lengths, and PS grafting density exert significant influences on the coassembly process. In low BCP concentration regime, the average size of s-micelles increases with BCP concentration and keeps unchanged at high concentration. The PS block length has a significant influence on the size of s-micelles. The average size increases with an increase in PS block length. For a BCP with long solvophilic PDMAEMA block, it is energy favorable to self-assemble into b-micelles, but to coassemble into s-micelles. With an increase in PDMAEMA block length, the morphology of the s-micelles changes from wormlike/spherical structures to spherical structures and to smaller spherical structures. The average size of the s-micelles coassembled by PS brushes at a lower grafting density is smaller than those coassembled by PS brushes at a higher grafting density.

Surface properties of materials are strongly dependent on surface chemistry and surface structures. The fabrication of hierarchical surface nanostructures will endow solid surfaces with new functionalities and properties. In this research, we propose the polymerization-induced surface self-assembly (PISSA) approach for surface reconstruction. In this approach, two macro-CTAs, one grafted on silica particles and the other molecularly dissolved in solution, were used in reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization, and surface micelles (s-micelles) with different morphologies and sizes on silica particles were fabricated. Kinetics studies demonstrate that there are two critical points on a plot of ln­([M]0/[M] t ) vs polymerization time, corresponding to the onsets of surface assembly and the self-assembly of block copolymers. The morphology of s-micelles is dependent on the monomer conversion and the length of macro-CTA. For macro-CTA with short chain length, with an increase in monomer conversion the s-micelles experience a morphology change from spherical s-micelles to layered structures. For macro-CTA with long chain length, the average size of s-micelles increases with monomer conversion. In this research, we demonstrate PISSA can be used as a versatile method for surface modification.

Well-defined polymer–protein bioconjugates are widely used in therapeutics and biocatalysis. One of the challenges in the synthesis of bioconjugates is the efficient separation of the target conjugate molecules from reaction systems. In this research, surface coassembly of polymer brushes and polymer–protein bioconjugates is investigated, and it is demonstrated that the coassembly approach can be applied in the purification of polymer–protein bioconjugates. Bovine serum albumin-poly­(N-isopropylacrylamide) (BSA-PNIPAM) bioconjugates were synthesized by the “grafting from” approach, and PNIPAM brushes on silica particles were prepared by the “grafting to” approach. PNIPAM brushes on silica particles are able to coassemble with BSA-PNIPAM at a temperature above the lower critical solution temperature of PNIPAM. Two-layer surface structures with collapsed PNIPAM in the inner layers and BSA in the outer layers are formed on the silica particles. The size of the silica particles and molecular weight of PNIPAM on the bioconjugates exert influences on the coassembly. The coassembly approach can be used in the purification of bioconjugates. After repeated coassembly centrifugation-release cycles, all the BSA-PNIPAM bioconjugates can be removed from the reaction solutions, and the purified bioconjugates are obtained.

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 1 H NMR, 13 C 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-SiO 2 ). Coassemblies of PEG/PS Y-shaped polymer brushes and linear PEG-b-PS BCPs with different PS block lengths were studied. In THF/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-SiO 2 and PEG-b-PS 89 , only spherical micelles are formed on silica particles. At high BCP concentrations, Yshaped polymer brushes and PEG-b-PS 143 chains coassemble into surface wormlike structures on silica particles. In the coassembly of PEG/PS-SiO 2 and PEG-b-PS 306 , 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.