Ureate anion-catalyzed ring-opening polymerization (ROP) of CO₂ -derived lactones: rapid catalysis through pK_a matching

The kinetics of ureate anion-catalyzed ring-opening polymerization (ROP) of 3,6-diethyltetrahydro-2H-pyran-2-one (DEtP) and 3-ethyl-6-vinyltetrahydro-2H-pyran-2-one (EtVP), CO₂ -derived lactones, is reported. Polymerization rates were significantly enhanced by matching the pK_a of a particular urea and the pK_a-H of the base, with stronger bases and more weakly acidic ureas leading to universally fast catalysis—reducing reaction times from earlier-reported days to minutes/seconds. In parallel, 2-ethylheptanoic acid (EHA), a byproduct from DEtP monomer synthesis, was discovered to completely suppress polymerization, even in trace amounts. This highlights the need for rigorous purification protocols to ensure high monomer purity. These results demonstrate the dual importance of chemical purity and rational catalyst design for achieving rapid ROP of CO₂ -derived DEtP and offer a framework for advancing sustainable polymer synthesis.