## 2 Results and Discussion  
Catalytic systems were obtained in the reaction of ZnEt\({}_{2}\) with natural GAc (or PGAc) at a molar ratio of 3:1. _rac_-LA polymerizations in the presence of ZnEt\({}_{2}\)/GAc or ZnEt\({}_{2}\)/PGAc catalytic systems were carried out at zinc to monomer molar ratio of 1:50 or 1:100 at 40-80 \({}^{\circ}\)C (Scheme 1, Tables 1-4). Toluene, tetrahydrofuran or dichloromethane were used as a reaction medium. The effects of the reaction medium, temperature and reaction time on the monomer conversion, product molecular weight, as well as the microstructure of the synthesized polyesters were investigated. We found that ROP of _rac_-LA produced PLAs terminated with hydroxyl chain end groups under these conditions. The chemical structures of the obtained PLAs were confirmed by \({}^{1}\)H- or \({}^{13}\)C-NMR and FT-IR studies (see the Experimental Section). The molecular weight and polydispersity of the synthesized polyesters were also determined. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Entry**} & \multicolumn{2}{c}{**Molar Ratio**} & \multirow{2}{*}{**Temp. (\({}^{\circ}\) C)**} & \multirow{2}{*}{**Time (h)**} & \multirow{2}{*}{**Yield 4 (\%)**} & \multirow{2}{*}{**Conv. \({}^{\circ}\) (\%)**} & \multirow{2}{*}{**\(M_{\rm e}\) (Da)**} & \multirow{2}{*}{**PD \({}^{\circ}\ \begin{table}
\begin{tabular}{l c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Entry**} & \multicolumn{3}{c}{**Molar ratio**} & \multirow{2}{*}{**Medium**} & \multirow{2}{*}{**Tem.** **(C)**} & \multirow{2}{*}{**Time **(h)**} & \multirow{2}{*}{**Yield * (\%)**} & \multirow{2}{*}{**Conv.** **b (\%)**} & \multirow{2}{*}{**\(M_{\rm e}\) **(Da)**} & \multirow{2}{*}{**\(PD\)** *  & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} & \multicolumn{1}{c}{} \\ \hline \hline CLA 38 & 1/50 & THF & 40 & 16 & 29 & 31 & 2000 & 1.35 & 7 & 2300 & 1800 & 0.71 & 2.82 & 0 \\ PLA 39 & 1/50 & THF & 40 & 48 & 40 & 46 & 2900 & 1.69 & 18 & 3300 & 2600 & - & - & 0.19 \\ PLA 40 & 1/50 & THF & 60 & 48 & 47 & 51 & 3300 & 2.61 & 22 & 3700 & 3100 & - & - & 0.49 \\ PLA 41 & 1/100 & THF & 40 & 48 & 38 & 41 & 5100 & 1.82 & 12 & 5700 & 4700 & - & - & 0.07 \\ PLA 42 & 1/100 & THF & 60 & 48 & 39 & 44 & 5500 & 2.39 & 26 & 5600 & 4900 & - & - & 0.44 \\ PLA 43 & 1/50 & CH\({}_{2}\)Cl\({}_{2}\) & 40 & 16 & 15 & 17 & 1200 & 1.74 & 18 & 1500 & 1100 & - & - & 0.27 \\ PLA 44 & 1/50 & CH\({}_{2}\)Cl\({}_{2}\) & 40 & 48 & 36 & 39 & 2400 & 2.89 & 29 & 2600 & 2100 & - & - & 0.53 \\ PLA 45 & 1/100 & CH\({}_{2}\)Cl\({}_{2}\) & 40 & 48 & 32 & 34 & 4200 & 1.92 & 23 & 4700 & 3800 & - & - & 0.38 \\ \hline \hline \end{tabular}  
* \({}^{*}\) calculated by the weight method: \({}^{\rm B}\) calculated from \({}^{\rm B}\)H-NMR analysis (spectra of a crude reaction mixture; the conversion has been calculated by the integration of the characteristic signal of the monomer (\(\delta=5.03\) ppm) and the polymer chain (ranged from \(\delta=5.13\) to \(5.18\) ppm): \({}^{\rm B}\) determined by GPC; \(M_{\rm e}\) corrected by a factor of \(\alpha=0.58\)[41]: \({}^{\rm B}\) MC (macrocylic content) determined by MALDI TOF MS; \({}^{\rm B}\) determined by MS; \({}^{\rm B}\)H-NMR; \(p_{2}\)—coefficient of stereoselectivity calculated from the equation presented in [45]: \(T\)—transesterification coefficient [15]: \(L_{i}=2/P_{i}\)—average length of \({}^{\rm L}\)xly units [46].  
\end{table} 
Table 4: Ring-opening polymerization of \(n\)c-LA in tetrahydrofuran and dichloromethane in the presence of ZnEt\({}_{2}\)/PGAc catalytic system. \begin{table}
\begin{tabular}{l c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Entry**} & \multicolumn{3}{c}{**Molar ratio**} & \multirow{2}{*}{**Tem. ** **(C)**} & \multirow{2}{*}{**Time **(h)**} & \multirow{2}{*}{**Yield * (\%)**} & \multirow{2}{*}{**Conv.