Priming the pores of mesoporous silica nanoparticles with an in-built RAFT agent for anchoring a thermally responsive polymer

Abstract

Abstract RAFT mesoporous silica nanoparticles (MSNs) have been synthesized for the first time via co-condensation of an organoalkoxysilane RAFT agent, 1-phenylethyl(3-(triethoxysilyl)propyl)carbonotrithioate, with tetraethoxysilane (TEOS) in aqueous basic cetyltrimethylammonium bromide. The stability of the organoalkoxysilane RAFT agent during the synthesis of MSNs was established using solution NMR and UV–visible spectroscopies. The RAFT-MSNs were then used for elaboration with N-isopropylacrylamide (NIPAM) via controlled surface-initiated RAFT polymerization. The success of the incorporation of the organoalkoxysilane RAFT agent into the silica network, and polymerization of PNIPAM was confirmed with TGA, FT-IR, UV–visible spectroscopy, 13C and 29Si solid state NMR spectroscopy. The effect of the organoalkoxysilane based RAFT agent and PNIPAM grafting on the morphology, size and surface area of the resulting MSNs was investigated using SEM, TEM, XRD, DLS and BET analysis. The appearance of carbon signals in 13C solid state NMR, T signals in 29Si solid state NMR and C H stretching signals in FT-IR establishes that we have successfully obtained organic-inorganic hybrid materials. The pore area calculated using Barrett-Joyner-Halenda (BJH) analysis was 87.8 m2 g−1 for control-MSNs, 91.1 m2 g−1 for RAFT-MSNs and 132.9 m2 g−1 for PNIPAM-MSNs. The thermoresponsive behaviour of PNIPAM grafted inside the pores of MSNs was studied by dye as well as drug loading experiments at variable temperatures, followed by characterization using confocal laser scanning microscopy. The green and red fluorescence corresponding to fluorescein and doxorubicin respectively was strongly retained in the PNIPAM-MSNs after 24 h of incubation at 25 °C while lack of fluorescence after 24 h incubation at 35 °C, demonstrates the thermoresponsive behaviour of the polymer being grafted inside the pores of mesoporous silica nanoparticles.