TECHNOLOGY FOCUS - POLYMERS - Preparation (Claimed): Preparation of (I) comprises: reacting oligo- or polymer compound (II) with a halogenating agent at -20degreesC to 140degreesC in an inert solvent to obtain a haloaromatic oligo- or polymer compound (III); reacting (III) in a nitrogen free solvent or its mixture with O-silylated oxygen compound of the trivalent phosphorus at above 100degreesC in presence of a catalyst comprising at least a metal such as platinum of periodic system of the element to obtain an oligo- or polymer, silylated polyphosphonic acid compound (IV); and reacting the obtained (IV) with an organic compound exhibiting azide hydrogen atom to obtain (I).Preferred Components: The halogenating agent is brominating agent. The nitrogen free solvent is benzophenone, diphenylether and/or diphenylsulfone. The O-silylated oxygen compound of trivalent phosphorus is HP(OSiR2R3R4)2 and/or P(OSiR2R3R4)3. The membranes are selective permeable membrane in demineralization, sewage cleaning, dialysis and ionic extraction and -retention. EXAMPLE - Ultrason (RTM: Polysulfone) (100 g) was heated and dissolved in chloroform (400 ml) at 70degreesC for 20 minutes. Further a solution of bromine (58 g) in chloroform (100 mol) was added and stirred. After 3 hours, starch (2.5 l) and a mixture of methanol/acetone in the volume ratio of 4:1 was added at 20degreesC. The obtained mixture was extracted with pure methanol over potassium hydroxide and subsequently dried at 100degreesC for 24 hours to obtain brominated precursor compound (P1). (P1) (10 g) and aqueous free nickel(II) chloride (270 mg) were reacted at 190degreesC. Diphenyl ether (3 g) and a polymer were reacted at 200degreesC, under nitrogen atmosphere for 1 hour. Further tributyl phosphite (6.55 g) was added in drop wise, stirred for 30 minutes and heated at 180degreesC for 8 hours. The obtained mixture was cooled under a mixture of methanol/acetone/hydrochloric acid mixture of diphenyl ether and nickel (in the volume ratio of 100:50:2). The obtained product was mechanically minced, extracted with methanol for 12 hours and dried at 75degreesC to obtain phosphonic acid polymer (9.30 g).