Ring‐opening polymerization of ε‐caprolactone using perfluoroalkanesulfonates and perfluoroalkanesulfonimides as organic catalysts

Abstract

AbstractWe examined ring‐opening polymerizations (ROPs) of ε‐caprolactone in toluene at 25–50 °C catalyzed by perfluoroalkanesulfonates and perfluoroalkanesulfonimides as organic catalysts. The ROPs proceeded quickly using these super Brönsted acids as catalysts. We synthesized poly(ε‐caprolactone)s (Mn = 4.8 × 103–13.5 × 103) with low polydispersity (Mw/Mn = 1.10–1.48). These strong Brönsted acids catalyzed living polymerizations of ε‐caprolactone. After polymerization, Nf2NH was recovered and reused. To survey solvents, CHCl3 and tetrahydrofuran (THF) were used instead of toluene as solvents for polymerization. When THF was used as a solvent, not only ε‐caprolactone, but also THF was polymerized and incorporated into the polymer chain (incorporated THF ratio; 6–10%). We investigated the reaction kinetics and activation thermodynamics of the organic catalysts. The activation energy and the activation enthalpy values for the ROPs of ε‐caprolactone using the catalyst having electron‐withdrawing ligand were smaller, but the activation entropy value is more negative. Moreover, the ranked values of the activation enthalpy for the reaction well parallel the polarity of solvents. The ranked values of the activation free energies well parallel those of the times required for polymerization completion. Our findings indicate that the super Brönsted acids are excellent catalysts for rapid ROP of ε‐caprolactone: they are more active than N, N‐dimethylaminopyridine (DMAP) or stannous (II) 2‐ethylhexanoate [Sn(Oct)2]. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011