TECHNOLOGY FOCUS - POLYMERS - Preferred Membrane: The structure (B) and crosslinked structure (A) are bonded to each other via 2 or more covalent bonds. Structure (B) consists of carbon and hydrogen and preferably the main skeleton section of (B) is of formula (1);-(CH2)n- (1)n = 2-20.More preferably, the main skeleton section of (B) is of formula (2);-(CH2)m-(Ar)-(CH2)m- (2)m = 0-10; andAr = a 6-30C arylene structure.Structure (C) and structure (A) are bonded to each other via 1 or more covalent bonds. The main skeleton section (C) has a hydrocarbon structure with at least one amino group and the other portion consisting of carbon and hydrogen. Preferably, (C) has at least one structure from those of formulae (3) and (4);-(CH2)a-(NH-(CH2)b)c-NH-(CH2)a- (3)-(CH2)a-(NH-(CH2)b)c-NR1R2 (4)a and b = 1-12;c = 0-5; andR1 and R2 = H 1-12C alkyl or 1-12C aryl.Structure (C) is incorporated at 0.01-1 equivalent per equivalent of structure (B). Agent (D) is incorporated at 0.01-3 equivalents per equivalent of the total of structures (A), (B) and (C) and at least per equivalent of structure (C).Preferred Method: The compound (E) is of formula (5) and compound (F) is of formula (6) or (7);R3 = methyl, ethyl, propyl and phenyl;X = a group of formula (1) or (2);Y = a group of formula (3);Z = a group of formula (4); andx and y = 0 or 1.The mixture is incorporated with water and the third step is followed by a fourth step in which the mixture formed into a film is cured at 100-300degreesC.    TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Membrane: The agent (D) is an acid, preferably a heteropolyacid. It is incorporated at 0.01-3 equivalents per equivalent of the total of structures (A), (B) and (C) and at least per equivalent of structure (C). SPECIFIC COMPOUNDS - Agent (D) is at least one of phosphotungstic acid, phosphomolybdic acid and silicotungstic acid.    EXAMPLE - A solution of 0.79 g of 1,8-bis(triethoxysilyl)octane and 0.07 g of bis(trimethoxysilylpropyl)amine dissolved in 1.5g of isopropyl alcohol was prepared. Another solution of 0.69 g of phosphotungstic acid n-hydrate dissolved in 1.5 g of isopropyl alcohol was separately prepared. These solutions were mixed with each other, stirred for several minutes, and poured into a petri dish of polystyrene. The mixture was left at room temperature for 15 hours and heated at 80degreesC for 10 hours in a saturated steam atmosphere and at 100degreesC in an oven, to prepare a transparent, flexible membrane. It was washed in a flow of water at 60degreesC for 2 hours, before it was analyzed.    The membrane was subjected to a bending functional test and it was found that it could be bent and was kept flexible. To evaluate proton conductivity, the membrane was coated with carbon paste on both sides, to which platinum plates were fast adhered. It was analyzed for its impedance in a frequency range of 0.1-100 kHz. The sample was supported in an electrically insulated closed container, and measured for its proton conductivity at varying temperatures in a water vapor atmosphere (95 to 100% RH), where cell temperature was increased from room temperature to 160degreesC by a temperature controller. Proton conductivity at 60degreesC and 95% RH was 1.1 x 10 power 3 and proton conductivity at 140degreesC and 100% RH was 8.1 x 10 power 3. The membrane was heated at 140degreesC for 5 hours in an autoclave in a saturated steam atmosphere. The treated membrane was evaluated for its heat resistance by the visual and bending functional tests. There was no change in the membrane before and after the treatment.    A comparative membrane was prepared as above, except that 0.89 g of 1,8-bis(triethoxysilyl)octane and 0.20 g of 0.1N hydrochloric acid were used. It was found that this membrane could be bent and was kept flexible, but the proton conductivity at 60degreesC and 95% RH was less than 10 power -8 and the proton conductivity at 140degreesC and 100% RH was impossible to measure.