The present invention relates to a process for producing composite materials which consist essentially of a) at least one oxidic phase; and b) at least one organic polymer phase; by copolymerizing at least one compound A selected from aryloxy metalates, aryloxy semimetalates and aryloxy esters of nonmetals which form oxo acids and are different than carbon and nitrogen with at least one compound B selected from formaldehyde and formaldehyde equivalents, in a reaction medium which is essentially anhydrous, wherein the compound B is used in such an amount that the molar ratio of formaldehyde to the aryloxy groups in compound A is at least 0.9:1.