Oligosaccharide-based block copolymers: metal-free thiol-maleimide click conjugation and self-assembly into nanoparticles

Amphiphilic oligosaccharide-based block copolymers (OBCPs) are able to self-assemble either into nanoparticles with biocompatible oligosaccharides corona in aqueous solution or in sub-nanopatterned thin-films originating from the high incompatibility between the different blocks. For these reasons, these biosourced OBCPs are valuable structures for applications in nanomedicine and nanoelectronics. Up to now, the synthesis of those OBCPs was obtained through grafting-onto method using Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC). However, complete removal of metal catalyst residues from the resultant copolymer chains is critical and hampers electronic and biomedical applications. In this study, we report an efficient and convenient metal-free click chemistry approach consisting in coupling thiol-containing oligosaccharide blocks to maleimide-terminated polystyrenes. Upon self-assembly in water, spherical micelles of similar size than those obtained by Cu(I)-catalyzed azide-alkyne cycloaddition were formed as evidenced using dynamic light scattering and transmission electron microscopy techniques.