secondary cross linking agents the primary cross linking agents used in the invention are formaldehyde furfural and hexamethylenetetramine hexamine formaldehyde is introduced either in solution in the pore former or as solid paraformaldehyde ch 2 o x formaldehyde cross links phenolic moieties forming u2014 ch 2 u2014 and u2014 ch 2 u2014 o u2014 ch 2 u2014 bridges at ratios depending on the ph of the reaction mixture methylene bridges are the only ones formed in strong acidic and strong alkali media whereas at ph 39 s close to neutral either type of bridges appear water is formed as the stoichiometric secondary condensation product at a level depending on the type of bridge formed 1 mole per mole of formaldehyde in the case of the methylene bridges or 1 mole h 2 o per 2 moles ch 2 o in the case of the ether bridges the u201c condensation u201d water may then influence the phase separation and mesopore formation process by reducing the compatibility of the water containing pore former with the resin domain depending on the pore forming solvent being used complete cross linking of phenol with formaldehyde by methylene bridges requires approximately a 1 to 1 5 molar ratio of the reagents taking into account the formation of some ether type bridges the phenol to formaldehyde molar ratio in the resin compositions of the invention is preferably maintained at 1 6 to 1 8 level this requires an additional 9 to 12 weight parts of formaldehyde paraformaldehyde per 100 weight parts of novolac resin furfural differs from formaldehyde in that the electrophilic reactivity of its carbonyl group is supplemented by the high nucleophilic activity of the heterocyclic moreover ring scission and consecutive.