New fluorinated polymers containing the pentafluorothio group have been prepared from SF5Br and the appropriate fluoroolefin under reaction temperatures of 90±5°C and autogeneous pressures of up to 90 atmosphere for periods of four days to two weeks. With ethylene, FCH2CH2Br and SF5CH2CH2Br were formed. A new monomer addition product, SF5CF2CF2Br, is also reported for the first time.