AbstractThe preparation and properties of a unique new class of polymers containing polyhedral borane cages as part of the backbone polymer chain are described. The synthesis of polyamides, polyesters, polyureas, and polyurethanes proceeds from suitably chosen B10and B12polyhedral borane dicarbonyls, diols, and diisocyanates by typical condensation polymer techniques. Each complementary monomer may be a borane compound, but more often higher molecular weight products are provided when one monomer is a conventional organic reagent such as an aromatic diisocyanate. The polyamides prepared from 1, 12‐B12H10(CO)2and organic diamines were crystalline and soluble, but molecular weight were limited because the amidation reaction was reversible and/or the amide linkage could be split by nucleophilic attack by some solvents. The polyurethanes prepared from Na2B12H10(OH)2and aromatic diisocyanates were high molecular weight and relatively more stable. Clear, colorless, tough films were prepared. These polymers were soluble in many polar solvents and exhibited typical polyelectrolyte behavio