The radical telomerisation of trifluoroethylene (TrFE) with dimethyl phosphite (DMP) was investigated to synthesize fluorinated monoadducts bearing a phosphonate end-group such as HTrFEP(O)(OCH3)2. Among various radical initiators, di-tert-butyl peroxide (DTBP) was the most efficient one at 80–140 C. This telomerisation protocol successfully yielded mainly the monoadduct of TrFE and DMP. A structural study of the TrFE-DMP monoadduct was carried out using 1H, 13C, 19F and 31P NMR spectroscopies and showed that a mixture of dimethyl-1,2,2-trifluoroethylphosphonate and dimethyl-1,1,2-trifluoroethyl- phosphonate was obtained. The best experimental conditions to reach high yields of monoadduct were achieved at T = 140 C, using initial molar ratios R0 = [DMP]0/[TrFE]0 and C0 = [DTBP]0/[TrFE]0 of 3 and 0.05, respectively, and a reaction time of 15 h. Higher telomeric adducts were also detected by MALDI-TOF mass spectrometry.