The radical copolymerization of methyl trifluoroacrylate (MTFA) with vinylidene fluoride (or 1,1-difluoroethylene, VDF), initiated by tert-butyl 2,2-dimethylperoxypropanoate, is presented. The kinetics of copolymerization was investigated in a series of eight reactions for which the initial [VDF](0)/ [MTFA](0) molar ratios ranged between 14.5/85.5 and 88.7/11.3. The composition of copolymers, i.e., the molar ratios of VDF and MTFA monomeric units in the copolymers, was determined by F-19 NMR spectroscopy mainly. The reactivity ratios, r(i), determined according to the Tidwell and Mortimer law, were assessed to be: r(VDF) = 0.30 +/- 0.03 and r(MTFA) 0 at 50 degreesC, which clearly shows tendency of the copolymerization system toward alternation copolymerization. Copolymerizations at high monomer conversions were also attempted and showed a good incorporation of MTFA and rather high molecular weights (up to 26000).