are e g amines carboxylic acids acid chlorides thiocarbamates thiocarbamic acid chloride diazo compounds esters and sulphides and so on modification of polycondensates containing u03b3 aminopropyl groups can be effected for instance by treating the polycondensate for 30 to 60 minutes at room temperature with an aqueous 2 5 glutaric aldehyde solution the diazo derivative can be made for example by conversion with p nitrobenzoyl chloride reduction of the nitro group to the amine or diazotization with nitrous acid if the silicic acid heteropolycondensate contains aniline groups already through the use of a suitable functional silane it can be immediately diazotized with nitrous acid by conversion of the amino groups of the silicic acid heteropolycondensate with thiophosgene isothiocyanate derivatives can be produced the following examples illustrate the invention in the examples specific surface is measured according to bet the diameter of the small pores by the nitrogen adsorption isothermal and the diameter of the large pores by the sem method 2 95 ml of tetramethoxysilane 4 25 ml of dimethyldiethoxysilane 7 30 ml of methanol and 2 31 ml of 6 n hydrochloric acid approx 17 by weight of catalyst were combined at room temperature in the order given and allowed to stand for 20 days with the exclusion of air after drying for 16 hours in a drying tunnel at 120 u00b0 c a white granular product with a specific surface of 270 m 2 g was obtained the coarse pores showed an average diameter of about 1 u03bcm and the small pores an average diameter of about 2 to 5 nm 122 00 ml of methanol 48 00 ml of tetramethoxysilane.