A nitrogen-rich cyanuric–urea polymer (CUP) was synthesized in a single step under solvent free conditions. The catalyst was characterized by microanalysis, FT-IR, XRD, ¹³C/¹⁵N CP-MAS NMR, SEM, TEM, EDX spectroscopy, nitrogen sorption–desorption studies and CO₂ TPD. The CUP was used as an efficient catalyst for the cycloaddition reaction of epoxides with CO₂ under solvent and additive free conditions. The product cyclic carbonates were obtained with high conversion and excellent selectivity. This method also provides a straightforward approach with great application to access polyurethane/polyhydroxyurethane in a single step with good yield.