Imprinting the location of an in-built RAFT agent and selective grafting of polymer chains inside or outside the pores of mesoporous silica nanoparticles

Abstract

Abstract Mesoporous silica nanoparticles (MSNs) primed with RAFT agent were synthesized via co-condensation of tetraethoxysilane (TEOS) and organoalkoxysilane based RAFT agent. The nature of the R group in organoalkoxysilane based RAFT agent was varied in order to control the preferential location of polymer grafting. Two different RAFT agents were prepared, one RAFT agent contained phenyl ethyl as R group, and other RAFT agent contained isobutyric acid as R group. The stability of the organoalkoxysilane based RAFT agents was confirmed employing UV–Visible spectroscopy and 1H solution NMR spectroscopy techniques. Succeeding this RAFT functionalized MSNs preparation, surface-initiated RAFT polymerization was carried out using N-isopropylacrylamide (NIPAM). RAFT and polymer functionalized MSNs were then characterized by diverse techniques such as FT-IR, TGA, UV–Visible spectroscopy, surface area measurement, X-ray photoelectron spectroscopy (XPS), 13C and 29Si solid-state NMR spectroscopy. The outcome of utilizing different types of organoalkoxysilane based RAFT agent on the morphology was examined using SEM and TEM. Spherical and cuboid shape was observed in the case of RAFT–COOH–MSNs and RAFT-Ph-MSNs respectively. Higher percentage of polymer grafting was observed in case of PNIPAM–COOH–MSNs in comparison to PNIPAM-Ph-MSNs. The realization of preferential grafting of polymer on exterior or interior surface of RAFT MSNs was established using pore size/volume analysis by BET as well as by XPS. The characteristic resonances in 13C and 29Si solid-state NMR and characteristic vibrations in FT-IR, confirms successful synthesis of organic-inorganic hybrids. The analysis of thermoresponsiveness of PNIPAM grafted MSNs was experimented by drug loading and release studies at different temperatures as well as by confocal laser scanning microscopy.