## 2 Results and Discussion
Figure 5: MALDI TOF MS spectrum of PCL obtained in the presence ZnEt\({}_{2}\)/GAc catalytic system (**PCL-5**). Figure 6: MALDI TOF MS spectrum of PCL obtained in the presence ZnEt\({}_{2}\)/PGAc catalytic system (**PCL-9**). It is worth mentioning that the macrocyclic content (_MC_) for PCLs obtained in the presence of a ZnEt\({}_{2}\)/PGAc catalytic system is apparently small when compared to the _MC_ for PCLs obtained in the presence of a ZnEt\({}_{2}\)/GAc catalytic system (Table 1). For example, the _MC_ value was 18% for **PCL-3**, 54% for **PCL-5**, 0% for **PCL-9** and 7% for **PCL-11**, respectively. When, the ROP of the CL process was carried out in the presence of ZnEt\({}_{2}\)/GAc catalytic system at 40 \({}^{\circ}\)C within 48 h, _CP_ were not formed. For comparison, the _MC_ was 0% for the reaction carried out in the presence of a ZnEt\({}_{2}\)/PGAc catalytic system at 40-60 \({}^{\circ}\)C within 48 h or at 80 \({}^{\circ}\)C within 6 h. However, on the basis of the intensity of **H-PCL-OH** peaks for products obtained in the presence of a ZnEt\({}_{2}\)/PGAc catalytic system, it can be estimated that the content of _CP_ does not exceed 14 mol %. The yield of the ROP process ranged from 32% to 63% for ZnEt\({}_{2}\)/GAc and from 47% to 96% for ZnEt\({}_{2}\)/PGAc catalytic systems. For ZnEt\({}_{2}\)/GAc and ZnEt\({}_{2}\)/PGAc the corresponding monomer conversion values were in the range of 44%-69% and 52%-100%, respectively. The yield of the CL polymerization increased with increasing the reaction temperature and time (Table 1). For example, the reaction yields were as follow 72% (the reaction temp. 40 \({}^{\circ}\)C, catalyst/monomer feed ratio 1:100), 90% (60 \({}^{\circ}\)C, 1:100) and 96% (80 \({}^{\circ}\)C, 1:100) for **PCL-8**, **PCL-10** and **PCL-12**, respectively. When the process was carried out in the presence of (ZnEt\({}_{2}\)/PGAc) catalytic systems at the molar ratio of catalyst to monomer 1:100 (reaction temp. 80 \({}^{\circ}\)C), the reaction yields were: 67% for **PCL-15** (reaction time 6 h), 85% for **PCL-16** (reaction time 12 h) and 96% for **PCL-12** (reaction time 48 h). The viscosity molecular mass (_Mv_) values for PCLs were in the range of 2200-6400 Da (for ZnEt\({}_{2}\)/GAc) and 3100-12,400 Da (ZnEt\({}_{2}\)/PGAc). For comparison, _Mn_ determined from GPC for PCLs obtained in the presence of ZnEt\({}_{2}\)/GAc or ZnEt\({}_{2}\)/PGAc was in the range of 1900-6200 Da (_PD_ 1.40-1.78) and 2300-12,300 Da (_PD_ 1.39-1.89), respectively. The GPC values were adequately corrected using a factor of 0.47 [21, 22]. Figure 7: MALDI TOF MS spectrum of PCL obtained in the presence ZnEt\({}_{2}\)/PGAc catalytic system (**PCL-11**). As shown in Table 1, the average molecular mass of PCL is dependent on the Zn-based catalysts/CL molar ratio and the reaction time. The influence of the catalyst/monomer feed ratio on the average molecular weight of PCL was studied at two levels (1:50 and 1:100). It was found that the average molar mass of polymers increased with a feed ratio of Zn/CL decrease. For example, the \(M_{n}\) determined from GPC was 4500 Da for **PCL-9** (molar ratio 1:50) and 10,500 Da for **PCL-10** (molar ratio 1:100). As shown in Table 1, the \(M_{n}\) values calculated from NMR were consistent with the \(M_{n}\) determined by GPC. This indicated that the \(M_{n}\) of the obtained PCLs can be relatively well controlled by the molar ratio of monomer to catalysts systems. The CL monomer was completely consumed within 48 h at 60 or 80 \({}^{\circ}\)C, when the ROP process was carried out in the presence of ZnEt\({}_{2}\)/PGAc catalytic system. In comparison, the maximum conversion for ROP catalysed by ZnEt/GAc was 69% within 48 h at 80 \({}^{\circ}\)C. This indicates that ZnEt\({}_{2}\)/PGAc is a more effective catalytic system in promoting the polymerization of CL than ZnEt\({}_{2}\)/GAc. This is probably a result of the fact that in the first case only alcoholate active species are formed, whereas in the second case carboxylate species are also formed.