Preparation and characterization of nanocellular poly(phenylquinoxaline) foams. A new approach to nanoporous high-performance polymers

This work deals with a new strategy for the elaboration of macro- to nanoporous materials. The adopted scheme involves the in-situ generation of foaming agents (CO2 and isobutene) during the thermal treatment of a poly(phenylquinoxaline) (PPQ) film bearing thermolabile (tert-butyloxycarbonyl, i.e., Boc) groups (PPQ-Boc). For this purpose, a bis-diketone monomer having phenolic groups has been first synthesized and polymerized with a bis-diamine monomer. The resulting PPQ was postmodified by introducing Boc groups. After a kinetic and mechanistic study of the Boc thermal decomposition reaction, the influence of different experimental parameters on the final porosity formation has been investigated, such as the foaming temperature which is a key parameter. The porous materials obtained were characterized by different techniques (density, SEM, TEM) in order to determine the cell density as well as the size and morphology of the porous structure. Depending on the thermal treatment conditions, our strategy enables to obtain a wide range of porous materials, from nanoporous (10 nm, 10(16) cells/cm(3)) to macroporous (200-700 nm, 10(12) cells/cm(3)).