Copolymers containing 4-vinylpyridine as common monomer with tert-butyl acrylate and acrylic acid of different comonomer compositions were synthesized and characterized. Copolymer composition was determined by elemental analysis, from which monomer reactivity ratios (MRR, r) were estimated using straight line intersection procedures such as Fineman-Ross and Kelen-Tüdõs methods and a nonlinear one, the Reactivity Ratios Error in Variables Model. In this case, the values of MRR are r4VPy = 0.046 and r tBA = 0.054 (for 4VPy-co-tBA), and r4VPy = 0.0 and rAA = 0.610 (for 4VPy-co-AA). A copolymer tending to the alternation and another containing isolated units of one of the monomers between small blocks of the another one were obtained, depending on the chemical nature of the comonomers. The different proposed comonomer distributions are analyzed in terms of the obtained MRR values and compared with related systems. The MRR are connected with structural properties of the monomers such as polarity, aromaticity and electron delocalization