AbstractLight‐scattering and viscosity measurements are reported for fractions of poly(decamethylene perfluorosebacate). Intrinsic viscosity (dL/g) relationships at 25°C are [η] = 1.55 × 10−4Mv0.70in chloroform and (η) = 8.8 × 10−4Mv0.50ins‐tetrachloroethane. From these data the characteristic ratio is found to beCθ= 6.3 ± 0.5, indicating that the perfluoroalkane chain is not much more extended than an alkane chain. The solid semicrystalline polymer melts at 45°C, and its x‐ray powder pattern suggests a structure different from that of poly(decame