Preparation and characterization of polysilsesquioxane particles containing UV-absorbing groups

Abstract

Organotrialkoxysilanes (OTAS) containing bulky UV chromophores were polymerized under basic conditions to prepare insoluble spherical polysilsesquioxane (PSQ) particles potentially useful as UV blocking ingredients in sunscreens. The OTAS used in this study were 3-aminopropyltrimethoxysilyl-p-methoxycinnamamide (APTMSMCA), 3-aminopropyltriethoxysilyl-p-ethoxycinnamamide (APTESMCA), 3-aminopropyltrimethoxysilyl-p-N,N′-dimethylaminobezamide (APTMSDMABA), and 3-aminopropyltriethoxysilyl-p-N,N′-dimethylaminobenzamide (APTESDMABA). Mixtures of insoluble spherical particles, soluble solids, and insoluble monolithic solids were produced in various yields depending on the reaction conditions and the nature of the chromophore. The molar extinction coefficients of PSQ particles were 1/2 to 1/4 of those of corresponding unreacted chromophores and OTAS. The λ max and extinction coefficients of the PSQ particles varied according to their sizes. In vitro sun protection factor (SPF) values of petrolatum containing 10 wt% of the particles were between 10 and 21. The photostability of polyAPTMSMCA and polyAPTMSDMABA particles were significantly poorer than those of APTMSMCA and APTMSDMABA. Copolymerization of APTMSDMABA and methyltrimethoxysilane (MTMS) significantly improved the photostability. The particles dispersed in water and silicon oil showed photomechanical effects under UV light that were most likely caused by heat released during the relaxation process.