Influence of butyl group of tin chloride initiators on the non-isothermal DSC ring-opening polymerization of ε-caprolactone: The studies of kinetics, mechanism and polymer synthesis

The kinetics of ring-opening polymerization (ROP) of epsilon-caprolactone (epsilon-CL) initiated by tin(II) chloride (SnCl2), dibutyltin(IV) dichloride (Bu2SnCl2) and tributyltin(IV) chloride (Bu3SnCl) was successfully investigated by nonisothermal DSC technique. The steric effect of butyl group of these tin chloride initiators on the catalytic performance of the ROP of epsilon-CL was studied by isoconversional kinetics methods. From isoconversional kinetics analysis by both Friedman and Kissinger-Akahira-Sunose (KAS) methods, the activation energy (E-a) values for the ROP of epsilon-CL initiated by SnCl2 were lower than Bu2SnCl2 and Bu3SnCl, respectively. The average values of frequency factor (A) for the ROP of epsilon-CL with SnCl2, Bu2SnCl2 and Bu3SnCl are 2.05 x 10(4), 1.34 x 10(8) and 2.64 x 10(8) min(-1), respectively. The kinetics results clearly demonstrated that the reactivity of SnCl2 > Bu2SnCl2 > Bu3SnCl in the ROP of epsilon-CL The effectiveness of all tin chloride initiators in the synthesis of poly(epsilon-caprolactone) (PCL) was investigated via bulk polymerization. The highly reactive SnCl2 produced high number average molecular weight PCL ((M) over bar (n) = 3.5 x 10(4)-1.1 x 10(5) in a short polymerization time. The increasing of butyl group in tin chloride initiators reduced the effectiveness in the synthesis of high molecular weight PCL. Furthermore, the mechanism of the ROP of epsilon-CL with tin chloride initiators was also studied and proposed through the coordination-insertion mechanism.