The synthesis of original cotelomers based on 3,3,3-trifluoropropene (TFP) and vinylidene fluoride (VDF) with a general formula: R-F-[CH2-CF2](n)-[CH2-CH(CF3)](m)-I (where n = 1-63, m = 2-640, and R-F = (CF3)(2)CF) was achieved by sequential and random cotelomerizations in the presence of RFI. The radical cotelomerizations were initiated by thermal decomposition of different peroxide and persulfate initiators either in bulk, in solution (in the presence of acetonitrile or 1,1,1,3,3-pentafluorobutane as the solvents), and in aqueous process (emulsion). Different adducts were obtained in good yield (50-70 wt %) with a relative proportion of each adduct depending on (i) the R-0 = [RFI](0)/([TFP](0)+[VDF](0)) initial molar ratio, (ii) the reaction temperature, and (iii) C-0 = [In](0)/[TFP](0)+[VDF](0)). Random cotelomerization gave higher yields than those obtained from the sequential cotelomerization. When the concentration of the chain transfer agent increased, the molecular weights of the resulting poly(VDF-co-TFP) cotelomers decreased and showed that the R-0 ratio targeted the molecular weights (similar to 700-66,000 g mol(-1)). Some of the obtained molecular weights were exceptionally high for a (co)telomerization. The kinetics of the radical cotelomerization of VDF and TFP led to the determination of the reactivity ratios of both comonomers (r(VDF) = 0.28 +/- 0.07 and r(TFP) = 2.35 +/- 0.26 at 75 degrees C). (C) 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 3964-3981, 2009