Five dialkyl-substituted and three phenyl substituted polygermanes were electrochemically synthesized. Among them, dibutyl-, diyentyl-, and dihexyl-substituted polygermanes gave the best synthetic results, i.e., relatively high yields (25-45%), high current efficiency (25-50%), high molecular weights (M-w : 10,000-25,000), and long absorption maxima (lambda(max) : 324-327 nms). Thus obtained polygermanes showed the discontinuous thermochromic changes known for the polymers. Syntheses of the corresponding polysilanes under the same conditions gave better yields (50-70%), better current efficiency (50-80%), slightly larger molecular weights (M-w : 15,000-35,000), but shorter absorption maxima (lambda(max) : 313-316 nms). The reaction mechanism was discussed in detail. It was suggested in the discussion that more back-biting reactions, which is one of the causes for the decrease of the yield and the molecular weight, occur in the later stages of electrolysis. In order to know if molecular weights and yields are decreasing in the later stages of electropolymerization, syntheses with 40, 60, 80, and 100% electricity of the theoretical value were carried out. Synthesis with 80% electricity of the theoretical value gave the best results. (C) 1998 Elsevier Science Ltd. All rights reserved.