Ring‐closing depolymerization of poly(ε‐caprolactone)

Ring‐closing depolymerization of poly(ε‐caprolactone) in toluene solution with catalytic amounts of Bu 2 Sn(OMe) 2 results in a mixture of cyclic oligomers, the equilibrium concentration of which corresponds to the concentration predicted according to the Jacobson‐Stockmayer theory. ε‐Caprolactone, however, is absent from this reaction mixture. When poly(ε‐caprolactone) is depolymerized in the melt at 260°C in the presence of a catalyst, beside ε‐caprolactone its cyclic dimer and trimer are distilled off. The composition is dependent on the catalyst used, e.g., Bu 2 Sn(OMe) 2 produces 95,4 wt.‐% of ε‐caprolactone and 3,7 wt.‐% of its dimer while with Ti(OiPr) 4 (iPr: isopropyl) 51,4 wt.‐% ε‐caprolactone and 49,6 wt.‐% of its dimer are obtained. Block copolymers containing poly(ε‐caprolactone) result in a similar product distribution, however, the second block may influence the rate of decomposition. The activation energy of the catalysed (0,5 mol‐% Bu 2 Sn(OMe) 2 ) and uncatalysed ring‐closing depolymerization were determined to be 63 kJ/mol, and 87 kJ/mol, respectively.