AbstractThe intrinsic viscosity, sedimentation and diffusion of a series of branched, multichain poly‐α‐amino acids having a poly(L‐lysine) backbone and poly(γ‐benzylL‐glutamate) and poly (β‐benzylL‐aspartate) side chains was studied at room temperature in dimethylformamide. The molecules were found to be extremely compact structures in which the molecular backbone is either lying along the major axis in a slightly twisted configuration (the longer the side chain the smaller the twist) or is coiled up in the form of a disk with backbone and side chains coplanar. Heat treatment (to 70°C.) introduces only small changes in the hydrodynamic parameters showing that the heat‐labile aggregates detected by light scattering are reversibly broken up during the hydrodynamic measurements. The above structural information concerns the initial metastable conformation of the molecules which is irreversibly destroye