Miniemulsion SI-ATRP by Interfacial and Ion-Pair Catalysis for the Synthesis of Nanoparticle Brushes

Densely grafted polymer/inorganic nanoparticle hybrids were synthesized via a surface-initiated activator regenerated by electron transfer (SI-ARGET) atom transfer radical polymerization (ATRP) of n-butyl acrylate (BA) under ion-pair and interfacial catalysis in miniemulsion (hydrodynamic diameters from 105 to 128 nm) with ascorbic acid (AsAc) as the reducing agent. The use of a single-catalyst system in dispersed media allowed the preparation of hybrid materials using a very low catalyst loading (as low as 100 ppm of [Br-Cu-II(L)](+) relative to monomer) and obtaining high monomer conversion (up to 70%) without macroscopic gelation. The resulting polymers exhibited narrow molecular weight distributions (D <= 1.31), and the polymer-grafted nanoparticles showed excellent size uniformity. Dispersions in organic solvents (e.g., tetrahydrofuran) were stable without any particle aggregations. Subsequent chain extension of the particle brushes with tert-butyl acrylate (tBA) proved the livingness of the polymerization and high retention of chain-end fidelity. The developed miniemulsion SI-ARGET ATRP technique with interfacial and ion-pair catalysis offers numerous advantages for the preparation of nanoparticle brushes over the traditional hydrophobic ATRP process. These include a high monomer conversion, high grafting density, better control over polymerization rate, high chain-end livingness, and the use of a very low amount of copper catalyst.