TECHNOLOGY FOCUS - POLYMERS - Preferred Method: The method (P1) further involves drying the cross-linked sol-gel like material to form a cross-linked aerogel. The sol-gel like material is dried super-critically with liquid carbon dioxide or is air-dried. In the method (m1), the drying is conducted at ambient pressure and at a temperature of at least 4 (preferably at least 20, especially at least 200, particularly 300) degrees C. The drying is by freeze-drying.Preferred Components: The sol-gel like material is substantially filled with a solvent. The sol-gel like material is based on silica.    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Components: The cross-linking agent is an isocyanate, a diisocyanate, an acid anhydride, an acylchloride, a bis(acid anhydride) or a bis(acylchloride). The cross-linking agent comprises an attached group selected from an absorbant, a catalyst, a fluoriphore, a bio-molecule, a redox active label or a reactive group. The solvent is selected from a component (A), propylene carbonate, ethyl acetate or butyrolactone. (A) is water, ketone, alcohol, ester, carbonate and/or lactone. The alcohol is methanol or ethanol. The ketone is acetone. The cross-linking agent is in a (A). The isocyanate is a monoisocyanate, a diisocyanate, a triisocyanate, a tetraisocyanate, a polyisocyanate and/or an oligoisocyanate (preferably hexamethylene diisocyanate, poly(hexamethylene diisocyanate), toluene diisocyanate, diphenylmethane diisocyanate, an aliphatic polyisocyanate and/or triphenylmethyl triisocyanate). (S1) is an organic solvent selected from 1-20C alcohol, 1-20C alkane, 1-20C cycloalkane, 1-20C alkene, 1-20C cycloalkene, 1-20C alkyne, aryl, 1-20C alkane substituted aryl, 1-20C alkene substituted aryl or 1-20C alkyne substituted aryl (preferably 5-10C alkane).Preferred Composition: The cross-linking agent is present in a concentration of at least about 2 (preferably at least 5, especially at least 1000, particularly at least 2000) wt.%.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Components: The silica is prepared from alkoxy silica via an acid or a base-catalyzed route. EXAMPLE - A diisocyanate cross-linked tetramethoxysilane Sol-Gel Monolith was prepared by mixing a component (A) (containing tetramethoxysilane (514 ml) and methanol (3.839 ml) with a component (B) (containing methanol (4.514 ml), water (1.514 ml) and concentrated ammonium hydroxide (20 microl) thoroughly to form the sol, which was poured in polyethylene cylindrical vials. The molds were covered with parafilm. To facilitate removal of the gels from the polyethylene molds, the bottom cup was covered with a Teflon-tape lining. The sol gels in the molded at room temperature in 10 minutes, and the resulting gels were left in the molds to age (i.e., complete polymerization and cross-linking) for 2 days. Subsequently, the bottom covers of the molds were removed together with the Teflon lining, and the gels were pushed gently out of their molds directly into vials filled with methanol (one gel per vial). The pores of the gel was then filled with a diisocyanate solution by washing the gel four times for eight hours per wash with methanol, propylene carbonate, and then a mixture containing propylene carbonate and poly(hexamethylene diisocyanate) in succession. During the last wash, the gels were heated to 100degreesC for three days, and were then cooled to room temperature. The wash solution was decanted and the gels were washed with propylene carbonate one time for eight hours. The gels were then washed in a mixture of propylene carbonate and acetone (1:1, v/v) one time for eight hours, followed by washing in a mixture of propylene carbonate and acetone (1:3, v/v) one time for eight hours. The gels were then washed in acetone four times for eight hours per wash. Following the acetone wash, the gels were dried super-critically with carbon dioxide.