Comparison of Metal Alkoxide Initiators in the Ring-Opening Polymerization of Caprolactone

Abstract

Four metal tert-butoxides, namely: aluminum (III) tert-butoxide, Al (Ot-C4H9)3, tin (II) tert-butoxide, Sn (Ot-C4H9)2, titanium (IV) tert-butoxide, Ti (Ot-C4H9)4, and lithium tert-butoxide, Li (Ot-C4H9), were used as initiators in the bulk ring-opening polymerization (ROP) of ε-caprolactone (CL). The polymerizations were carried out at 120 °C for 72 hrs. It was found that the Al (Ot-C4H9)3 only partially dissolved in the CL monomer and gave a low % conversion. The Li (Ot-C4H9) initiator did not dissolve and gave no polymerization. In contrast, the Sn (Ot-C4H9)2 initiator dissolved completely, albeit very slowly, and gave a high % conversion. The Ti (Ot-C4H9)4 initiator was by far the easiest and quickest to dissolve and also gave a high % conversion. Consequently, Ti (Ot-C4H9)4-initiated polymerization was studied further by dilatometry at 120°C. From the kinetic results, a first-order rate constant, kp, of 0.120 l mol-1 min-1 was obtained.