NOVELTY - Modified polymers, polymer membranes or polymer mouldings, obtained by reaction of polymers containing carbonyl groups in the main chain or side chains with organometallic compounds, followed by hydrolysis to give the corresponding polymers etc. with hydroxyl groups.    USE - The modified polymers are used as blend components in proton-conducting blend membranes for membrane fuel cells or membrane electrolysis; modified polymer membranes are used in membrane processes, fuel cells and membrane electrolysis (claimed).    ADVANTAGE - A new class of modified polymers derived from polymers with side-chain carbonyl groups or engineering polymers with main-chain carbonyl groups. These polymers can be modified as such, or as moulded products or membranes, e.g. to achieve hydrophilic/hydrophobic/biochemical modification at the surface.    DETAILED DESCRIPTION - Modified polymers (Ia), polymer membranes (Ib), or polymer mouldings (Ic), obtained by reacting polymers, membranes or mouldings containing carbonyl groups (a) in the main chain or (b) in side chains with metal-organic compounds in solution, in suspension or on the surface, resulting in the following addition reactions for type (b) and (a) respectively:    MR2 = any organometallic compound which can undergo addition reactions with carbonyl groups;    R1, R2 = any organic residues which do not react with MR2;    Poly = any polymer residue    . INDEPENDENT CLAIMS are also included for    (1) (1) a method for the production of (Ia) by adding a solution of the starting polymer in inert solvent to the organometallic compound (II) (optionally in solvent, optionally in excess) at -80 to +80degreesC, optionally under inert gas, reacting at -80 to +80degreesC and working up by addition of alkanol (2-10 fold excess) to destroy excess (II), addition of water (2-10 fold excess), (optional) precipitation in a 2-20 fold excess of 3-15% mineral acid followed by filtration, precipitaton or suspension of the reaction mixture in a 2-20 fold excess of alcohol (methanol, ethanol or propanol) or water or aqueous mineral salt solution (NaCl, NaHCO3, Na2SO4 etc.) or other precipitation medium followed by filtration, washing, drying at elevated temperature and (optionally) reduced pressure, and optional redissolution followed by work-up as above    (2) (2) a method for the production of surface- or bulk-modified (Ib) and (Ic) by reacting the membrane or moul ding with a solution of (II) at -80 to +80degreesC and working up as above    (3) (3) forming (Ia) to produce membranes for use in membrane processes or possibly in membrane fuel cells or membrane electrolysis.