## 2 Results and Discussion  
The effect of various parameters on the yield of ROP of CL and the average molecular weight of obtained PCL using new Zn-based catalysts has been studied. The homopolymerization of CL was carried out in the presence of the ZnEtz/GAc or ZnEtz/PGAc catalytic systems at 40-80 \({}^{\circ}\)C within 6-48 h (Figure 1, Scheme 1). The catalytic systems were obtained in the reaction of ZnEtz with GAc (or PGAc) at a molar ratio of 3:1. Toluene was used as the solvent. The molar ratio of the catalyst ([Zn]\({}_{0}\)) to a given monomer was 1:50 or 1:100. The reaction yields and the average molecular weight of the obtained PCLs are summarized in Table 1.  
The structure of the obtained PCLs was confirmed by \({}^{1}\)H- or \({}^{13}\)C-NMR and FTIR techniques (see Experimental Section). Figures 2 and 3 show typical spectra of the synthesized polymeric products. Figure 1: Structure of gallic acid and propyl gallate. \begin{table}
\begin{tabular}{l l l l l l l l l l l l} \hline \hline
**Entry** & **Catalytic System** & \begin{tabular}{l} **Molar Ratio** \\ **[Zn]\({}_{\theta}\):** **[CL]\({}_{\theta}\)** \\ \end{tabular} & \begin{tabular}{l} **Temp.** \\ **(\%C)** \\ \end{tabular} & \begin{tabular}{l} **Yield** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{l} **Conv. \({}^{\mathrm{a}}\)** \\ \end{tabular} & \begin{tabular}{l} **\(M_{\mathrm{a}}\)** \\ **(\%)** \\ \end{tabular} & \begin{tabular}{l} **\(PD\)** \\ **(Da)** \\ \end{tabular} & \begin{tabular}{l} **\(MC\)** \\ \end{tabular} & \
\begin{tabular}{l} **\(M_{\mathrm{r}}\)** \\ **[Da]** \\ \end{tabular} &
\begin{tabular}{l} **\(M_{\mathrm{a}}\)** \\ **[Da]** \\ \end{tabular} \\ \hline  
& 1/100 & 80 & traces & - & - & - & - & - \\
**I-1** & GAc & 1/100 & 80 & 0 & 0 & - & - & - & - & - \\
**I-2** & PGAc & 1/100 & 80 & 0 & 0 & - & - & - & - \\ \hline \multicolumn{10}{l}{Reaction conditions: argon atmosphere, reaction time—48 h (* 6 h, ** 12 h); \({}^{\mathrm{a}}\) calculated from \({}^{1}\)H NMR analysis; \({}^{\mathrm{b}}\) determined by GPC; \(M_{\mathrm{a}}\) corrected by a factor of \(ca\). 0.47 [21,22]; \({}^{\mathrm{c}}\)\(MC\) (macrocyclic content) determined by MALDI TOF MS; \({}^{\mathrm{d}}\) determined by viscosity method (K = 1.94\(\cdot\)10\({}^{-4}\) dL/g and \(\alpha\) = 0.73) [23]; \({}^{\mathrm{e}}\) determined by \({}^{1}\)H-NMR.} \\ \end{tabular}
\end{table} 
Table 1: Homopolymerization of CL in the presence of ZnEt\({}_{2}\)/GAc and ZnEt\({}_{2}\)/PGAc catalytic systems. Figure 2: \({}^{1}\)H-NMR spectrum of the PCL (in CDCli). The MALDI TOF MS spectra of PCL contain several peaks; each component corresponds to a separate spectrum series (Figures 4-7). The first series of peaks is characterized by a mass increment of 114 Da, which is equal to the mass of the repeating CL unit in the PCL. It can be assigned to PCL terminated with a hydroxyl group (residual mass: _ca._ 41 Da, Na\({}^{+}\) adduct; **H-PCL-OH**, **Na\({}^{+}\)**). The peaks of the second population may be also attributed to PCL terminated with a hydroxyl group (residual mass: _ca._ 57 Da, K\({}^{+}\) adduct; **H-PCL-OH**, **K\({}^{+}\)**). The third and fourth series of peaks are probably from macrocyclic CL homopolymers (residual mass: _ca._ 1 Da, H\({}^{+}\) adduct; **PCL cycle**, **H\({}^{+}\)** or 23 Da, Na\({}^{+}\) adduct; **PCL cycle**, **Na\({}^{+}\)**). The content of cyclic products (_CP_) was estimated on the basis of the  
Figure 4: MALDI TOF MS spectrum of PCL obtained in the presence ZnEt\({}_{2}\)/GAc catalytic system (**PCL-3**). Figure 3: \({}^{13}\)C-NMR spectrum of the PCL (in CDCls). intensity ratio of the peaks for linear and cyclic PCL. The _CP_ was generally increased with increasing temperature and polymerization time. The results show that under the process conditions the polymer chain undergoes intramolecular transesterification (leading to the formation of _CP_), which is a typical phenomenon for the polymerization of cyclic monomers.