Insight into the effects of reaction conditions on metal-free surface-initiated atom-transfer radical polymerization of methyl methacrylate from SBA-15

Abstract

Mesoporous silica nanoparticles/polymer hybrid materials were prepared via metal-free surface-initiated atom-transfer radical polymerization (SI-ATRP). Self-synthesized mesoporous SBA-15 with surface hydroxyl groups was modified with (3-aminopropyl)-triethoxysilane, followed by anchoring of the ATRP initiator α-bromoisobutyryl bromide onto the surface via amide reaction. The SI-ATRP of methyl methacrylate was then carried out with fluorescein (FL) as a photocatalyst and trimethylamine (TEA) as an electron donor under irradiation with blue light. Thus, polymer chains grew directly from mesoporous walls. The hybrid materials were characterized by gel permeation chromatography, N2 adsorption/desorption measurements, and thermogravimetric analysis. The effects of the ligand/photocatalyst molar ratios, solvent, and the monomer/initiator molar ratios on grafting density, molecular weight, and molecular-weight distribution were investigated. The results show that a higher TEA/FL ratio led to a higher reaction rate and better controllability of the polymerization but also to a lower grafting density. These properties were also affected by the solvent. With an increasing monomer/initiator molar ratio, the grafting rate, molecular weight, and grafting density exhibited increasing trends.