The radical copolymerization of 2,2,2-trifluoroethyl a-fluoroacrylate (FATRIFE) with tert-butyl a-trifluoromethylacrylate (MAF-TBE) initiated by tertbutyl 2,2-dimethylperoxypropanoate was investigated in acetonitrile solution. A series of poly(FATRIFE-co-MAF-TBE) copolymers were synthesized with MAF-TBE compositions, determined by 19F NMR, ranging from 12 to 44 mol %. MAF-TBE incorporation was less than 50 mol % as this monomer underwent no radical homopolymerization. The obtained copolymers exhibited number-average molecular weights and polydispersity indexes ranging from 1.5 3 104 to 9.6 3 104 g/mol and from 1.5 to 3.1, respectively. The reactivity ratios were determined by the Kelen-Tu¨ dos method (rFATRIFE ¼ 1.71 6 0.01 and rMAF-TBE ¼ 0 at 74 8C) leading to random copolymers and alternating copolymers when the MAF-TBE molar ratio in copolymer is close to 50 mol %. Thermal and optical properties of the resulting polymers were examined. Glass transition temperatures of copolymers were varying from 89 to 108 8C. Modifying the compositions of these copolymers allowed a precise control over the refractive index measured at 633, 1320, and 1550 nm