Grafting of Poly(methyl methacrylate) with Different Sulfur-Containing End Groups on Gold Nanoparticles and Their Interfacial Assembly into Superlattice Films

Grafting polymer ligands on gold nanoparticles (AuNPs) by gold–sulfur (Au–S) bond is a facile way commonly employed to fabricate gold–polymer hybrid NPs (AuNP@polymer). By using the reversible addition–fragmentation chain transfer (RAFT) radical polymerization, it is convenient to present sulfur-containing end groups to polymer ligands, such as dithioester and trithioester groups, which can be usually transferred to thiol/thiolactone/disulfide groups by aminolysis reaction. However, these groups show different bonding effects to AuNPs. Especially for the thiolactone-terminated polymer, the weak bonding between thiolactone and AuNPs results in unstable AuNP@polymer conjugates, which further affects their assembly behavior. Here in this work, the effects of the end group on the surface-grafting of AuNPs were investigated by using poly(methyl methacrylate) (PMMA) ligands containing thiolactone/dithioester/disulfide/thiol end groups. By tuning the solvent property and the concentration of PMMA ligands, the thiolactone-terminated PMMA can be successfully grafted on the AuNPs, which has been regarded as a great challenge due to the weak bonding between gold and thiolactone. The grafting density of thiolactone-terminated PMMA can reach 0.5 chains/nm2, which is similar to that of disulfide/thiol-terminated PMMA. Moreover, the grafting density shows critical influence on the interfacial assembly behavior of AuNP@PMMA conjugates. By optimizing the assembly parameters, a superlattice film of AuNP@PMMA conjugates could be constructed, which may have promising applications in memory devices and sensors.