Varying Monomer Charge in SI-bioATRP Polymer Grafting from Mesoporous Silica

Polymer functionalization of mesoporous materials is crucial for a range of technologies including separation and sensing. In this study, we investigate the influence of monomer charge on enzyme-catalyzed polymerizations in mesoporous silica particles. Specifically, we copolymerize various charged monomers, such as potassium 3-sulfopropyl methacrylate (KSPMA), [2-(methacryloyloxy)ethyl]trimethylammonium chloride (METAC), 2-hydroxyethyl methacrylate phosphate (MEP), and 2-(dimethylamino)ethyl methacrylate (DMAEMA), with the positively charged fluorescent comonomer rhodamine-hydroxyethyl methacrylate (RhoB-HEMA), using enzyme-catalyzed surface-initiated atom transfer radical polymerization (SI-bioATRP). The polymerizations were performed in mesoporous spherical silica particles with average pore diameters of 23, 21, 17, and 12 nm using hemoglobin (Hb) as the catalyst. By adjusting the ratio of the fluorescent comonomer RhoB-HEMA to the charged monomers, the amount of the fluorescent comonomer in the polymers can be varied. Size-restricted accessibility of hemoglobin and small molecules, such as monomers to mesopores, especially when the pore neck diameter was smaller than the size of the protein, led to polymer formation mostly in the outer regions of the particles. Larger mesopores led to a homogeneous distribution of copolymers throughout the particles and to a higher overall polymer content within the mesoporous structures. These findings provide insights into the possibilities of functionalizing silica mesopores with polyelectrolytes via enzymatic SI-bioATRP, while the fluorescent comonomer enabled direct visualization of the copolymers by fluorescence microscopy. We anticipate that this approach will further advance the field of polymerization in confined nanoporous environments.