Germylenes bearing bulky amide groups have been copolymerized with various p-benzoquinone derivatives without any added catalyst to give a novel class of germanium-containing polymers having a tetravalent germanium unit and a p-hydroquinone unit alternatingly in the main chain. During the copolymerization, the germylene (reductant monomer) is oxidized and the p-benzoquinone derivative (oxidant monomer) is reduced ("oxidation-reduction copolymerization"). The resulting copolymers have high molecular weight (M(w); from 2.0 x 10(4) up to 1.4 x 10(6)) and most of them are soluble in common organic solvents. ESR studies of the copolymerization system and of the model reactions including the structural elucidation of the products gave the first clear-cut evidence for a biradical mechanism involving a germyl radical and a semiquinone radical. Trapping experiments using a disulfide, tetramethylpiperidinyloxy (TEMPO) radical, and a sterically hindered p-benzoquinone derivative further supported the biradical structure of the propagating polymer ends.