Diblock Copolymer Nanoparticles Act as Nanoreactors for the Synthesis of Sterically-Stabilized Inorganic Oxide Particles in Non-polar Media.

Abstract

Well-defined diblock copolymer nanoparticles are prepared via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of 2-hydroxyethyl methacrylate (HEMA) in a poly(α-olefin) oil at 90°C using a poly(lauryl methacrylate) (PLMA) precursor. The PHEMA cores of these nanoparticles are subsequently swollen with up to 30% w/w aqueous 0.3 M HCl based on the PHEMA mass and then used as nanoreactors for the in situ synthesis of silica or titania using either tetraethyl orthosilicate (TEOS) or titanium tert-butoxide, respectively. The PLMA-PHEMA nanoparticles are characterized by transmission electron microscopy, dynamic light scattering (DLS), and small-angle x-ray scattering (SAXS). The former technique indicates that core-swelling leads to a subtle change in copolymer morphology from pseudo-spherical to perfectly spherical nanoparticles. DLS and SAXS confirm the formation of near-monodisperse nanoparticles of 92-117 nm diameter with colloidal stability being retained after the nanoreactor syntheses. For the silicified nanoparticles, time-resolved turbidimetry and SAXS studies suggest a reaction timescale of around 50 min at 25°C. In this case, the final nanoparticle dispersion is highly transparent, whereas the corresponding titania-loaded nanoparticles produce a highly turbid dispersion. Thermogravimetric analyses indicate silica and titania mass loadings of 17% and 21%, respectively. In both cases the inorganic phase is amorphous rather than crystalline.