Abstract <p>Reactivity ratios have been determined for the free-radical copolymerization of methacrylic acid (<i>r</i> ₁) and isoprene (<i>r</i> ₂) in 1,4-dioxane. The reactivity ratios calculated according to the extended Kelen–Tüdõs method and the method recommended by IUPAC are found to be <i>r</i> ₁ = 1.12 ± 0.26 and <i>r</i> ₂ = 0.59 ± 0.22 and <i>r</i> ₁ = 1.10 (‒0.15 +0.22) and <i>r</i> ₂ = 0.60 (‒0.04 +0.05), respectively. Approaches to determining the configuration of isoprene units using ¹H NMR spectroscopy data are considered. It was established that up to 97% of isoprene units in macromolecules predominantly occur in 1,4-<i>trans</i> configuration. The content of 3,4-units is twice that of 1,2-units and does not exceed 4%. It was shown that macromolecules contain homosequences of comonomer units. 3,4-Units of isoprene are surrounded predominantly by <i>trans</i>-units. Based on the data of ¹H NMR spectroscopy and copolymerization reactivity ratios, a conclusion is made about the configuration of macromolecules as a whole. The dependence of the Harwood run number (microblockiness parameter) the average length of homosequences of units in macromolecules on the composition of the monomer mixture was revealed.</p>