Organic–inorganic hybrid polysilsesquioxane nanospheres as UVA/UVB absorber and fragrance carrier

Abstract

To avoid the photocatalysis property of inorganic UV absorbers, such as TiO₂ and ZnO nanoparticles, and to utilize the minimal transdermal penetration and non-sticky nature of particulate silica particles, whilst at the same time fully harnessing the UV absorption characteristics of organic chromophores, hybrid organic–silica particles with UVA/UVB absorptive chromophores as part of their network structures were synthesized. Two UV absorptive hybrid nanospheres, poly[propyl-4-methoxycinnamamide silsesquioxane] (PTES4C) and poly[propyl-2,4-dimethoxycinnamamide silsesquioxane] (PTES24C), were synthesized through the hydrolysis-polycondensation of triethoxysilylpropyl-4-methoxycinnamamide (TES4C) and triethoxysilylpropyl-2,4-dimethoxycinnamamide (TES24C), respectively. Optimization of the catalyst type (acid, base or self-catalysis) and solvent (ethanol) and monomer concentrations, led to a high yield (71–73%) preparation of the two nanospheres. The two spheres displayed good sun protection factor (SPF) and UVA protection factor (UVA-PF) when used in a gel based formulation. The labile and volatile fragrant citronellal could be effectively loaded into the PTES4C spheres at 35–48% (w/w) via the in situhydrolysis–polycondensation reaction under self-catalysis conditions, and the obtained citronellal-loaded nanospheres demonstrated clear sustained controlled release of the citronella characteristics.