Kinetic investigation and scale-up of bulk ring-opening copolymerization of L-lactide and ɛ-caprolactone in the presence of liquid tin(II) n-butoxide
摘要
This study investigates the effectiveness of liquid tin(II) n-butoxide (Sn(OnBu)2) as an initiator in the bulk ring-opening copolymerization (ROCOP) of L-lactide (LL) and ɛ-caprolactone (ε-CL). The objectives include examining the impact of initiator concentration and temperature on the kinetics of the polymerization. Kinetic parameters are analyzed using the proton-nuclear magnetic resonance spectroscopy (1H-NMR) technique. The findings reveal that increasing the initiator concentration enhances the final conversion percentage and the apparent rate constant (kapp), with kapp values of 8.21 × 10−3 min−1 for LL and 1.03 × 10−3 min−1 for ε-CL at 120 °C. Furthermore, the apparent rate constant increases with temperature, reaching a kapp of 7.00 × 10−3 min−1 at 150 °C for a 70/30 LL/ε-CL feed ratio. A comparative analysis with the conventional initiating system of tin(II) 2-ethylhexanoate (stannous octoate, SnOct2) and n-butyl alcohol (Sn(Oct)2/n-BuOH) indicates that liquid Sn(OnBu)2 gives a higher kapp under the same polymerization conditions. Remarkably, the activation energy (Ea) for Sn(OnBu)2 is lower (25.7 kJ mol−1 K−1) compared to that of the Sn(Oct)2/n-BuOH system (34.6 kJ mol−1 K−1). Additionally, copolymerization using liquid Sn(OnBu)2 provides poly(L-lactide-co-ε-caprolactone) (PLCL) with a higher-molecular weight (Mn = 5.4 × 104 g mol−1) than that obtained using the Sn(Oct)2/n-BuOH system (Mn = 2.8 × 104 g mol−1). These results demonstrate that liquid Sn(OnBu)2 is a highly effective initiator for the ROCOP of LL and ε-CL, suggesting its strong potential for scaling up production in industrial applications and commercialization.
Graphical abstract