## 2 Results and Discussion
### Chain Microstructures of Synthesized Copolymers
Moreover, the experimental results show that transesterification reactions are in minority in each case comparing with copolymerization. Equations (1) and (2) were applied to obtain the number-average sequence lengths of the lactidyl and caproyl sequences [28; 32]:  
Figure 4: Expanded \({}^{13}\)C-NMR spectra of carbonyl region of copolymer (B2) synthesized in [bmim][BF\({}_{4}\)] at 80 \({}^{\circ}\)C for 14 days. Figure 3: Expanded \({}^{13}\)C-NMR spectra of carbonyl region of PCL, PLA and copolymers of PCL and PLA synthesized in [bmim][NIT\({}_{2}\)] at 110 \({}^{\circ}\)C for 14 days; (**a**) PCL; (**b**) B6; (**c**) B3; (**d**) B9; (**e**) PLA. \[l_{LL}^{e}=\frac{[\text{LLLLLLLL}]+[\text{LLLLLC}]+[\text{CLLLLL}]+[\text{CLLC}]}{[ \text{CLLC}]+\frac{1}{2}([\text{CLLLLL}]+[\text{LLLLLC}])} \tag{1}\]  
\[l_{Cap}^{e}=\frac{[\text{LLCCL}]+[\text{CCLL}]+[\text{LLCC}]+[\text{CCC}]}{[ \text{LLCLL}]+\frac{1}{2}([\text{CCLL}]+[\text{LLCC}])} \tag{2}\]  
As it can be seen in Table 2, for copolymers synthesized in [bmim][NTf\({}_{2}\)], both \(l_{LL}^{e}\) and \(l_{Cap}^{e}\) values depend on the monomers feed ratio, and increased as the relative proportions of their respective monomer increased. In the case of [bmim][BF\({}_{4}\)] as a solvent, a stronger effect from the monomer feed ratio and temperature was observed for CL (\(l_{Cap}^{e}\): 4.44-23.56) than for LA (\(l_{LL}^{e}\): 1.23-2.87). Moreover, the higher \(l_{Cap}^{e}\) values reflect the higher reactivity ratio of CL and longer but fewer C sequences than LL sequences within the copolymer chain. Shorter \(l_{Cap}^{e}\) and \(l_{LL}^{e}\) values indicate that transesterification indeed occurred. A transesterification reaction rearranges the polymer sequences and leads to randomization. The degree of randomness (\(R\)) of the copolymer and the coefficient of the second mode of transesterification (T\({}_{\Pi}\)) were calculated from the following equations [28; 32]:  
\[R=l_{LL}^{R}/l_{LL}^{e}=l_{Cap}^{R}/l_{Cap}^{e} \tag{3}\]  
where \(l_{LL}^{e}\) and \(l_{Cap}^{e}\) are the experimental average length of the lactidyl and caproyl blocks, and \(l_{LL}^{R}\) and \(l_{Cap}^{R}\) are the average length of the lactidyl and caproyl blocks for the chains with random units distribution, as would be obtained by the complete transesterification via the first and the second mode, and it can be calculated from the following equations [28; 32]:  
\[l_{LL}^{R}=(k+1)/2k \tag{4}\]  
\[l_{Cap}^{R}=(k+1) \tag{5}\]  
\[\text{T}_{\Pi}=[CLC]_{e}/[CLC]_{R} \tag{6}\]  
where [\(CLC\)] is the experimentally determined concentration of \(CLC\) sequence from the \({}^{13}\)C-NMR spectroscopy, and [\(CLC\)]\({}_{R}\) is the theoretical concentration for completely random chains calculated via Bernoullian statistics:  
\[[CLC]_{R}=k^{2}/(k+1)^{3} \tag{7}\] \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multicolumn{4}{c}{**Microstructural Magnitudes of the Copolymers**} \\ \cline{2-5}  & \(l_{LL}^{e}\) & \(l_{Cap}^{e}\) & \(R\) & \(\text{T}_{\Pi}\) \\ \hline A2 & 1.96 & 7.41 & 0.50 & 0.08 \\ A3 & 1.52 & 12.88 & 0.25 & 0 \\ A5 & 2.25 & 23.56 & 0.17 & 0.03 \\ A6 & 1.23 & 16.14 & 0.21 & 0 \\ A8 & 2.87 & 4.44 & 0.80 & 0 \\ A9 & - & - & - & 0 \\ B2 & 2.04 & 5.67 & 0.38 & 0.04 \\ B3 & 3.52 & 5.53 & 0.41 & 0 \\ B5 & 2.20 & 10.66 & 0.28 & 0.01 \\ B6 & 2.08 & 14.38 & 0.23 & 0 \\ B8 & 6.47 & 2.66 & 0.99 & 0 \\ B9 & 5.81 & 2.48 & 0.67 & 0 \\ \hline \hline \end{tabular} \(l_{LL}^{e}\): experimental average length of lactidyl blocks; \(l_{Cap}\): experimental average length of caproyl blocks; \(R\): degree of randomness; T\({}_{\Pi}\): yield of the second mode of transesterification [17; 21].  
\end{table} 
Table 2: Chain microstructure of obtained copolymers.