Synthesis of Amphiphilic Poly(organosiloxane) Nanospheres with Different Core−Shell Architectures

Abstract

Core−shell and core−shell−shell nanospheres with different amphiphilicities were synthesized by sequential condensation of trimethoxymethylsilane (T), diethoxydimethylsilane (D), and the functional monomer (chloromethylphenyl)trimethoxysilane (ClBz-T) and mixtures thereof. The condensation was performed in aqueous dispersion in the presence of surfactant. Saturation of reactive surface SiOH groups with monofunctional trimethylsilane monomers prevents interparticle condensation and leads to nanoparticles, which are redispersable in organic solvents. The diameters of the particles range between 20 and 40 nm, depending on the composition. The thickness of the outer, nonfunctionalized shell is determined by asymmetrical flow field−flow fractionation (AF−FFF) and dynamic light scattering (DLS) of the core and core−shell particles, respectively. It varies between 1.5 and 3 nm and is proportional to the volume of added monomer. Incorporating (chloromethylphenyl)siloxane groups in the core and performing a subsequent quaternization reaction of dimethylaminoethanol yield amphiphilic nanospheres with an ionic, hydrophilic core and a hydrophobic outer shell. The amount of ionic moieties is found to be proportional to the amount of functional (chloromethylphenyl)siloxane groups incorporated in the spheres. Additionally, multiple shell topologies were successfully prepared, i.e., particles with a poly(dimethylsiloxane) (PDMS) core, an ionic inner and a hydrophobic outer shell. If linear PDMS chains forming the core are prevented to chemically bind to the inner shell, they may be removed by ultrafiltration, resulting in the formation of hollow spheres.