Aldehyde-Functional Diblock Copolymer Nano-objects via RAFT Aqueous Dispersion Polymerization

We report the rational design of aldehyde-functional sterically stabilized diblock copolymer nano-objects in aqueous solution via polymerization-induced self-assembly. More specifically, reversible addition-fragmentation chain transfer aqueous dispersion polymerization of 2-hydroxypropyl methacrylate is conducted using a water-soluble precursor block in which every methacrylic repeat unit contains a pendent oligo(ethylene glycol) side chain capped with a cis-diol unit. Systematic variation of the reaction conditions enables the construction of a pseudo-phase diagram, which ensures the reproducible targeting of pure spheres, worms, or vesicles. Selective oxidation of the pendent cis-diol groups using aqueous sodium periodate under mild conditions introduces geminal diols (i.e., the hydrated form of an aldehyde obtained in the presence of water) into the steric stabilizer chains without loss of colloidal stability. In the case of diblock copolymer vesicles, such derivatization leads to the formation of a worm population, indicating partial loss of the original morphology. However, this problem can be circumvented by cross-linking the membrane-forming block prior to periodate oxidation. Moreover, such covalently stabilized aldehyde-functionalized vesicles can be subsequently reacted with either glycine or histidine in aqueous solution, followed by reductive amination to prevent hydrolysis of the labile imine bond. ζ potential measurements confirm that this derivatization significantly affects the electrophoretic behavior of these vesicles. Similarly, the membrane-crosslinked aldehyde-functionalized vesicles can be reacted with a model globular protein, bovine serum albumin, to produce "stealthy" protein-decorated vesicles.