A highly reactive photobase catalytic system for sol-gel polymerization

In sol-gel polymerization of alkoxysilane precursors, base catalysts are usually employed to introduce textural properties. Herein, we show the feasibility and interest of a photobase-catalyzed sol-gel reaction to afford silicate films. Our inorganic polymerization is solvent-free, single-step and UV activatable with a mixture of α-aminoacetophenone (photobase generator), benzophenone (photosensitizer) and triphenylphosphine (oxygen scavenger). To date, the present tricomponent photolatent system generating N-alkyl morpholine tertiary amines represents one of the most efficient photobase generators reported so far in sol-gel chemistry. A combination of spectroscopic and electron microscopy techniques enabled to investigate the fundamental chemistry underlying alkoxysilane photopolymerization: reaction mechanism, hydrolysis kinetics and siloxane microstructure. Systematic comparison with a photoacid-catalyzed process revealed also the impact of the photocatalyst nature on film texture, morphology and optical properties.