Self-Assembled Amphiphilic Macromolecule Coatings: Comparison of Grafting-From and Grafting-To Approaches for Bioactive Delivery

A Versatile Strategy for Unimolecular Micelle-Derived Hollow Polymer Nanoparticles as General Nanoreactors

We reported the synthesis of a well-defined hollow polymer nanoparticle derived from star-shaped unimolecular micelles. β-Cyclodextrin was first applied as an efficient macroinitiator to prepare a star-shaped PCL via ring-opening polymerization (ROP). Then, the star-shaped PCL was modified to be a macro-RAFT agent for photoinduced electron/energy transfer-reversible addition-fragmentation chain transfer (PET-RAFT) polymerization of S-Cl monomers. The prepared unimolecular micelles can be photocross-linked under UV irradiation after a simple nucleophilic substitution reaction, which made -Cl groups to be -N₃ groups. After the selective removal of the PCL core, hollow polymer nanoparticles were achieved and exhibited to be a general nanoreactor strategy for the fabrication of nanocrystals with well-controlled architectures. Compared with unimolecular micelle templates, the nanocrystals prepared by hollow templates are absolutely pure as no polymer chains are embedded in the inorganic nanocrystals. In addition, by changing the concentration of the precursor, the structure of the nanocrystal can be changed from a normal spherical structure to a hollow structure.

Preparation of Well-Defined Poly(styrene-co-acrylonitrile)/ZnO Hybrid Nanoparticles by an Efficient Ligand Exchange Strategy

Poly(styrene-co-acrylonitrile) (PSAN)-capped ZnO nanoparticles (NPs) were synthesized by a "ligand exchange" method. First, octylamine (OA)-capped ZnO NPs were prepared by reaction of OA and zinc 2-ethylhexanoate (Zn(EH)₂). Then PSAN polymer ligands were synthesized by activators regenerated by electron transfer (ARGET) atom transfer radical polymerization (ATRP) and were efficiently exchanged with OA ligands on the ZnO particle surface benefiting from the relatively low boiling point of OA (175 °C). The morphology, content of ZnO, and grafting density of the nanocomposite were well controlled by altering the ratio between OA and polymer ligands as well as the molecular weight of PSAN-NH₂ used in the exchange reaction. The resulting ZnO/polymer nanocomposites were stable in THF with narrow size distributions and varying grafting densities from 0.9 to 2.5 nm^-2. With excess amount of polymer ligands, individual dispersed ZnO NPs were observed. However, with a limited amount of ligands, NPs clusters were formed, as confirmed by TEM and DLS.