In the polymer of transition-metal-bridged units of the formula (I) where A is an m-valent organic radical, T independently of one another are O or NH, Q independently of one another are CHR1—CH2 where R1 is H or optionally substituted C1-6-alkyl, R independently of one another are H, 2-pyridyl, 2-imidazolinyl, 2-imidazolyl, 2-thiazolinyl, 2-thiazolyl, 2-pyridazyl, 2-pyrimidyl, carboxyl, carboxylic ester radical, carboxamide radical, carboxylate, phosphonate, where at least one of the radicals R is different from H, M is Fe2+, Fe3+, Co2+, Co3+, Zn2+, Ru2+, Os2+, Ni2+, Z is SO42−, CH3OO−, BF4−, SF6−, Cl−, I−, PF6−, perchlorate, n is 1 to 10 000, m is 2 to 100, p is a number which corresponds to the charge balance within the polymer, the average molecular weight of the polymer is at least 15 000.