The development Of highly porous metal organic frameworks (MOFs) is greatly sought after, due to their wide range of applications. As an alternative to the,development of new structures, we propose to obtain new stable configurations for flexible MOFs by insertion of polymeric guests. The guests prevent the otherwise spontaneous closing of the host frameworks and result in stable opened forms. Introduced at a fraction of the maximal capacity, polymer chains cause an opening of the occupied nanochannels, and because of the MOF reticular stiffness, this opening is propagated to the neighboring nanochannels that become accessible,for adsorption. Composites were obtained by in situ,polymerization of vinyl monomers in the: nanochannels of an otherwise nonporous MOP, resulting in homogeneously loaded materials with a significant increase of porosity (S-BET m(2)/g);:in addition, by limiting the accessible configurations for the framework and forbidding the forbidding of a reactive intermediate, the polymeric guest prevented the thermal degradation of the host MOP even at very low loading (as low as. 3 wt %) and increased it's stability domain by more than 200 degrees C.