Ring-opening polymerization of ε-caprolactone using soluble tin(Ii) n-butoxide-l-lactide macroinitiators

Abstract

Novel soluble tin(II) n-butoxide-L-lactide macroinitiators (SnLL) were successfully synthesized from ring-opening polymerization (ROP) of L-lactide (LL) initiated by 4.0 and 8.0 mol% of tin(II) n-butoxide (Sn(OnBu)2) which were noted as SnLL4 and SnLL8, respectively. Chemical structures and thermal properties of these macroinitiators were completely characterized by Fourier transform infrared spectroscopy (FT-IR) and proton nuclear magnetic resonance spectroscopy (1H-NMR). Reactivity of the synthesized macroinitiators in the ROP of ε-caprolactone (ε-CL) was rapidly investigated by non-isothermal differential scanning calorimetry (DSC) technique. The polymerization exotherms for the ROP of ε-CL with SnLL8 occurred at lower temperature range than SnLL4 for all heating rates. From Friedman and Kissinger-Akahira-Sunose (KAS) isoconversional kinetics analysis, the values of activation energy (Ea) for the ROP of ε-CL with SnLL8 (Ea = 32.4-48.1 kJ/mol) were lower than SnLL4 (Ea = 54.9-98.1 kJ/mol). The efficiency of the synthesized macroinitiators in the bulk ROP of ε-CL was compared with conventional initiating systems of stannous octoate (Sn(Oct)2. The result showed that SnLL4 can control the synthesis of high molecular weight poly(ε-caprolactone) (PCL) more efficiently. The molecular weights of PCL decreased with increasing SnLL4 concentrations. From the obtained results, the novel SnLL macroinitiator was an effective initiator for the ROP of cyclic esters along with other beneficial properties such as being easier to handle and use.