A series of new well-defined copolymers containing the hydroxyl-functionalized monomer, caprolactone 2-(methacryloyloxy)ethyl ester (CLMA), and tert-butyl acrylate/methacrylate (tBuA/tBuMA) were synthesized via atom transfer radical polymerization (ATRP). The composition of copolymer strongly depended on the selection of comonomer pair. The relative reactivity ratios of comonomers determined by the Jaacks method indicated significantly higher reactivity of CLMA in methacrylate/acrylate system (r(CLMA) = 2.53, r(tBuA) = 0.40), whereas tert-butyl monomer was faster polymerized in case of two methacrylates (r(CLMA) = 0.61, r(tBuMA) = 1.63). These results were compared with that obtained for the CLMA/MMA system, which was closer to CLMA/tBuMA, giving r(CLMA) = 0.83 and r(MMA) = 1.20. The copolymer composition influenced decreased with an increase of CLMA content. the glass-transition temperatures (T(g)s), which