Catalysts 1 to 6 for ROP of LA. We next applied catalysts 1 to 6 toward ROP of LA and ROCOP of COS/PO, respectively (Table ). Exhibited activities of catalysts 1 to 4 in the ROP and ROCOP are in the same order, that is, 4 > 1 > 2 > 3. Catalyst 4 manifested the highest catalytic activity owing to its highest alkalinity, based on N,N-dimethylcyclohexylamine (pKa ~ 10.7 in H2O) with a higher basicity than N,N-dimethylbenzeneamine (pKa ~ 5.2 in H2O). In the case of catalysts 1 to 3, the tighter Lewis acid and base groups are believed to make the synergistic catalytic effect more pronounced, i.e., 1 > 2 > 3. This order was consistent with the order of exhibited catalytic activity, indicative of a positive effect of synergistic catalysis. ). Thus, the activation of LA by the three-site catalyst appears to be mainly through the thiourea moiety, in agreement with the hypothesized specific activation mechanism. Ofial and co-workers also disclosed little activation effect of ester carbonyl groups by boron compounds due to the weak Lewis basicity of carbonyls. By increasing the reaction temperature to 80 °C , the use of catalyst and). The resulting PLA also possesses a well-defined structure with α-OBn and ω-OH terminals, as revealed by matrix-assisted laser desorption/ionization time-of-flight mass spectroscopy (MALDI-TOF MS, Fig. ). These results suggested that ROP of LA with catalyst 4 is in an efficient and controlled manner.