Scale-up of the ring-opening polymerization of cyclic esters using tri-n-butyltin(IV) n-butoxide/aluminum tri-s-butoxide mixed initiators

Development of the large-scale synthesis (250 g and 500 g) of eco-friendly poly(ε-caprolactone) (PCL) and poly(L-lactide) (PLL) was successfully conducted via the ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) and L-lactide (LL) in the presence of effective tri-n-butyltin(IV) n-butoxide (nBu₃SnOnBu)/aluminum tri-s-butoxide (Al(OsBu)₃) mixed initiators for the first time. The effectiveness of nBu₃SnOnBu/Al(OsBu)₃ mixed initiators were studied in the neat and stock solution form. The heating processes such as one or two temperature polymerizations in the synthesis of PCL and PLL were investigated. Both heating processes could effectively produce PCL and PLL with weight average molecular weight (M_w) in the range of 3.6 × 10⁴–1.6 × 10⁵ g/mol and a %yield of up to 95%. Two-step heating process could produce a higher molecular weight of PCL than one step process with a shorter synthesis time. In the synthesis of PLL by using nBu₃SnOnBu/Al(OsBu)₃ mixed initiators, the racemization in the PLL chain was not observed in carbon-nuclear magnetic resonance spectroscopy (¹³C-NMR).