Notably, catalyst 4 produced isotactic-enriched PLA from ROP of rac-LA, which could be attributed to the synergistic catalysis of chiral thiourea and amine groups. The stacked homonuclear decoupled H NMR (Fig. ) revealed the obtained PLA at 25 °C (entry 4 in Table ) with tetrad ratios of mechanisms (Fig. ). To provide further evidence for the stereoselective mechanism, we monitored the kinetics of rac-, L-, and D-LA polymerization, respectively (Fig. ). Kinetic studies suggested that catalyst 4 preferentially polymerizes D-LA from rac-LA. Furthermore, polarimetry analysis of unreacted LA (at 82% LA conversion) revealed an enantiomeric excess (ee) of 34% for L-LA (Fig. ). Thereby, we figured out that CEC and ESC mechanisms occurred concomitantly in the ROP of LA, similar to the results reported by Dove and coworkers using a chiral Takemoto's catalyst. The PLA obtained (entry 4 in Table ) possesses a probability of forming meso dyads (Pm) of 0.84, as determined by the stacked homonuclear decoupled H NMR spectrum based on ESC statistics (Fig. ), and 0.88 calculated according to the C NMR spectrum (Fig. ). Owing to the high stereoregularity, the resulting PLA is crystalline and exhibits a melting temperature (Tm) of 146 °C, as determined by differential scanning calorimeter (DSC, obtained from first scan, Fig. ). The PLA obtained at 40 and 80 °C (entries 8 and 9 in Table ) also possess high Pm values of 0.83 and 0.80, respectively, as determined by C NMR (Figs. and). ). The copolymerization exhibited a regioselective manner, that is, the C=S double bond of COS and the methylene of PO are selectively attacked by growing anions, yielding copolymers with tail-to-head diads according to NMR analysis (Figs. and). No any side reactions including formation of cyclic thiocarbonates and homopolymerization of PO were observed. Catalyst 6 without thiourea groups resulted in 26%