This work concerns the investigation of porous poly(phenylquinoxaline)s (PPQ) films. The approach described relies on the in situ generation of foaming agents during the thermal curing of dense thin films of PPQ-containing thermolabile groups. For this purpose, a series of phenol-containing PPQ has been previously synthesized and then modified by grafting thermolabile tert-butyl carbonate groups (Boc) via a reaction involving the phenol groups. Thin dense films obtained by a solution casting method were thermally treated at different temperatures. The morphology of the resulting porous materials, characterized by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), is discussed in relation with the chemical structure of the polymers and to the thermal treatment conditions as well.