Insights into pore surface modification of mesoporous polymer-silica composites: introduction of reactive amines

Pore surface engineering of mesoporous materials is fundamental for the development of highly selective sorbents, solid catalysts or drug delivery systems. In the present study, tailored mesoporous amine-functionalized polymer–silica composites are synthesized using a two-step mesopore surface-confined polymerization technique. For this, a functional polymer, polychloromethylstyrene (PCMS), is first introduced as a uniform coating on the mesopore surface of mesoscopically ordered silica, e.g. SBA-15 or KIT-6 materials. In the second step, selected amines, as model functions, are attached to the polymer surface by nucleophilic substitution, generating a variety of nanoporous amino-polymer–silica composites. In particular, it is shown that this approach allows for a tuning of surface concentration of the organic groups either by varying polymer loading or by copolymerization of the CMS monomers with non-reactive monomers (styrene). Moreover, this method is suitable for facile introduction of diverse types of amine groups, e.g. secondary amines, diamines, linear or branched polyamines. The pristine mesoporous silica hosts and the different functional mesoporous polymer–silica composites are characterized in detail by nitrogen physisorption, powder X-ray diffraction, elemental analysis, thermogravimetry–differential thermal analysis coupled with mass spectrometry (TG-DTA/MS), attenuated total reflection-IR spectroscopy (ATR-IR) and scanning electron microscopy. In addition, the obtained functionalized mesoporous composites are proven active as base catalysts in the Knoevenagel condensation. From these investigations, it appeared that the preparation method should be highly flexible and appropriate to enable modulation of location and distribution of various functional groups within mesopores.