A Recoverable, Metal-Free Catalyst for the Green Polymerization of -Caprolactone

n-Propylsulfonic acid-functionalized porous and nonporous silica materials are evaluated in the ring-opening polymerization of -caprolactone. All catalysts allow for the controlled polymerization of the monomer, producing polymers with controlled molecular weights and narrow polydispersities. Polymerization rates are low, with site-time yields generally 1-3 orders of magnitude lower than metalbased systems. The catalysts are easily recovered from the polymerization solution after use and are shown to contain significant residual adsorbed polymer. Solvent extraction techniques are useful for removing most of the polymer, although the extracted solids are not effective catalysts in recycle experiments under the conditions used here. These new materials represent a green alternative to traditional metal-based catalysts, as they are recoverable and leave no metal residues in the polymer.