In-situ ¹H-NMR was used to obtain the copolymerization reactivity ratios of n-vinylpyrrolidone (VP) and 3-butyl-1-vinylimidazolium bromide (BVIM[Br]) using D₂O and V50 as solvent and initiator, respectively. The influence of the VP-BVIM[Br] monomer ratios was studied at 45, 50, and 55 °C using initial molar ratios of (30-70), (50-50), and (70-30), respectively. According to the monomer conversions, it was determined that electrostatic and thermodynamic effects controlled the reactions. As the reaction temperature increased, higher conversions were obtained, and in the VP-BVIM[Br] (70-30) ratio, the conversions were higher and close to 100% at 50 and 55 °C. This result was attributed to the lower ionic strength in the initial reaction system (0.46 mol/L). The monomer reactivities were calculated using the Mao-Huglin method and it was found that for the (70-30) VP-BVIM[Br] molar ratio at 45, 50, and 55 °C, $r_{\mathit{VP}}=r_{\mathit{BVIM}[\mathit{Br}]}=1$, obtaining random copolymers. For the VP-BVIM[Br] (30-70) molar ratio at 45 °C, the reactivity of VP was higher than that of BVIM[Br], $r_{\mathit{VP}}$= 2.1 > $r_{\mathit{BVIM}[\mathit{Br}]}$= 0.7, and for the VP-BVIM[Br] (50-50) molar ratio at 50 and 55 °C, the reactivity of VP was lower than that of BVIM[Br], $r_{\mathit{VP}}$= 0.5 < $r_{\mathit{BVIM}[\mathit{Br}]}$= 1.1 and ${\mathit{r}}_{\mathit{VP}}$= 1 < $r_{\mathit{BVIM}[\mathit{Br}]}$=1.5, respectively, obtaining a spontaneous gradient copolymer. The decomposition temperature of the copolymers depended on the initial molar ratio of the reaction mixture, finding that the higher the VP molar ratio, the higher the initial decomposition temperature (279 °C). Random copolymers reached higher T_g (174 °C) in comparison with those that featured a spontaneous gradient microstructure (152 °C).