Stop and restart of polycondensation reactions of highly reactive sol–gel precursors for nanoscale surface molding

Abstract

Sol–gel processes have been widely used for synthesizing functional inorganic and organic–inorganic hybrid materials. However, it has been challenging to apply mechanical nano-processing to sol–gel materials due to the rapid polycondensation and curing of concentrated precursors. In this study, a versatile polycondensation process for sol–gel precursors with intrinsic high reactivity has been developed by combining acid-catalyzed transesterification of metal alkoxides with addition of basic amine compounds. The reaction mixtures prepared using naphthalimide-derived alkoxysilanes result in long-term stable unhardened films after the removal of solvents, and their curing can be thermally restarted at the desired timing. Using this reaction method, nanoimprinted porous films have been obtained reproducibly from various organosilane precursors as well as some metal tetraalkoxides. The present approach would be applicable to a wide range of sol–gel reactions involving metal alkoxide species.