Design of highly porous melamine-based networks through a bicontinuous microemulsion templating strategy

Designing low density polymeric porous materials with defined pore sizes (diameters in the 100 nm range) still remains a real synthesis challenge. Here, for the first time, we present a strategy by which bicontinuous microemulsions are used as templating agents for the in-situ aqueous polycondensation of organic resins (melamine formaldehyde, MF). The behaviour of surfactants with different head-groups in systems including oil and MF-containing aqueous phase is studied. While many surfactants are not compatible with aqueous MF precondensates, here we report a non-ionic surfactant either used solely or along with anionic surfactants which prove to be successful at keeping bicontinuous microemulsion systems homogeneous even during early stages of polymerisation. However, upon acid-catalysis it becomes clear that the pore structure of the organic material is largely controlled by the kinetics of phase separation due to the sol-gel process rather than by the thermodynamic equilibrium of the template (microemulsion). Indeed, despite numerous attempts, stabilising the microemulsion interface with zero curvature (bicontinuous) has remained problematic. Instead, we show a new behaviour for the MF resin whereby non-spherical MF morphologies (i.e. thread-like structures) can be obtained by specific interactions between the aqueous amino resin and the acid counterions.