Tin(II) n-butyl l-lactate as novel initiator for the ring-opening polymerization of ε-caprolactone: Kinetics and aggregation equilibrium analysis by non-isothermal DSC

Abstract

The catalytic behavior of the novel tin(II) n-butyl l-lactate (Sn(OCH(CH3)COOnC4H9)2) initiator in the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) was firstly investigated by non-isothermal DSC. The Sn(OCH(CH3)COOnC4H9)2 initiator was successfully synthesized from the reaction of tin(II) chloride (SnCl2), diethylamine (Et2NH) and n-butyl l-lactate (CH3CH(OH)COOnC4H9). The synthesized Sn(OCH(CH3)COOnC4H9)2 was characterized by FT-IR, 1H NMR and 13C NMR techniques. The advantages of this initiator were high oxygen-moisture stability and solubility in common organic solvent. From DSC analysis, the polymerization rate of ε-CL was controlled by Sn(OCH(CH3)COOnC4H9)2 concentration. The average values of activation energy (Ea) obtained from Starink isoconversional method for the ROP of ε-CL initiated by 1.0, 2.0 and 3.0mol% of Sn(OCH(CH3)COOnC4H9)2 were 74±5, 72±5 and 68±2kJ/mol, respectively. Furthermore, the aggregation and non-aggregation equilibrium of Sn(OCH(CH3)COOnC4H9)2 initiator in the ROP of ε-CL was also investigated by non-isothermal DSC. The degree of aggregation (m) of initiator was rapidly determined using new derived equation based on non-isothermal DSC approach. The polymerization mechanism was also studied and proposed through the coordination-insertion mechanism.