To realize a high utilization ratio and easy recyclability of catalysts, polymeric ionic liquids as heterogeneous catalysts are tailored for the transformation of CO2 into cyclic carbonates. Herein, six types of self-polymerized polymeric ionic liquids are successfully synthesized by changing the substitutions. Amongst those catalysts, hydroxyl-rich polymeric ionic liquids, especially P(DMAEMA-EtOH)Br, exhibit the highest conversion (96%) to propyl carbonate, which is almost comparable to the reactivity of the bulk ionic liquid. Not only does the presence of a hydroxyl group considerably boost the reactivity, but it also enhances the thermal stability. Molecular dynamics calculations and XPS analysis confirm that the ability of P(DMAEMA-EtOH) Br to combine with epoxide is equivalent to that of its monomer. Dynamic light scattering data reveal that decreasing the hydrodynamic radius of the polymer particles contributes to greater exposure of active sites, resulting in high reactivity. In addition, synergistic catalysis mechanisms are proposed on the basis of the H-NMR studies. This eco-friendly process using polymeric ionic liquids provides a promising catalyst to convert CO2 into value-added chemicals.