The Ring‐Opening Polymerization of ε‐Caprolactone Catalyzed by Molybdenum Trioxide: A Kinetic Approach Study Using NMR and DSC Data

Abstract The bulk ring‐opening polymerization (ROP) of ε‐caprolactone (CL), catalyzed by molybdenum trioxide (α‐MoO 3 ), was investigated under nitrogen atmosphere at 150°C. Effect of monomer/initiator ([CL] 0 /[I] 0 , I = MoO 3 ) and monomer/initiator/co‐initiator ([CL] 0 /[I] 0 /[CoI] 0 , CoI = ROH and H 2 O) ratios on monomer conversion and molecular weight were determined. Bulk polymerization of CL was completed within 20 hours at 150°C for [CL] 0 /[I] 0 = 100. Propagation was first order in CL concentration and initiator at this temperature, being the rate constant of propagation k p equal to 2.27 × 10 −4 mol −1 l s −1 . Polymerization reaction was accelerated by the addition of small amounts of water and n‐octanol . In the presence of water (up to [CL] 0 /[H 2 O] 0 = 120), polymerization rate increases and was completed within 6 hours at 150°C; for higher amounts of water (150 to 180), lower conversions are observed. However, control of number‐average molecular weight was only efficient for [CL] 0 /[H 2 O] 0 = 20 and 30. In the presence of n‐octanol , degradation of polyester occurs at early stages of polymerization. Kinetic data for polymerization (obtained by 1 H‐NMR) were fitted to 14 different model reaction functions. It was found that a linear model represents better the conversion versus time plots for bulk polymerization, in agreement with the pseudo living nature of polymerization.