Templating Nanoporosity in Polyorganosilicates Using Reactive Dendrimers

It is shown that macroscopic phase separation of an otherwise immiscible dendrimer in a typical organosilicate can be kinetically hindered by incorporation of the dendrimers in a chemical network. Subsequent removal of sacrificial dendritic templates by thermolysis results in formation of nanoporous organosilicates. The phase separation of a dendritic diol in an organosilicate was studied by light microscopy. It was shown that macroscopic phase separation of such dendrimers could be drastically hindered by addition of a small amount of a triisocyanate, resulting in the formation of a polyurethane network bearing dendritic wedges at moderate temperatures. Curing of the organosilicate at elevated temperatures creates an interpenetrating network, in which the phase separation of dendrimers is prohibited because of topological constraints. Small-angle X-ray scattering revealed that pore sizes of approximately 12 nm can be generated upon thermolysis even in a matrix containing 70 wt % of dendrimer. The results were in qualitative agreement with field emission SEM images of the cross section of the coatings.