## 3 Results and Discussion
### Characterization of Raw Terpolymers  
In the case of PLGA copolymers, features such as the composition considering laticide stereoisomeric forms and the value of \(M_{n}\) are indicated as some of the most important in the design of a drug formulation [18]. In this study, three terpolymers based on D,L-LA or L-LA, GA, and TMC with \(F_{LL}\) in the range of 57.1-65.4 mol%, \(F_{GC}\) in the range of 14.7-18.3 mol%, and \(F_{TMC}\) in the range of 18.9-24.6 mol% with \(M_{n}\) of 21.4, 59.4, and 76.8 kDa were synthesized (Figure 5 and Table 3). The application of terpolymers containing TMC as drug carriers may significantly change the features of drug carriers in the areas of matrix degradation, release, and the bioavailability of drug substances in comparison to PLGA copolymers [18; 19; 20; 21; 22; 23; 24]. Figure 5: \({}^{1}\)H NMR spectra of raw terpolymers (Td,L 21 raw, Tl 59 raw, and Tl 77 raw) (600 MHz, DMSO-d\({}_{6}\), 80 \({}^{\circ}\)C). \({}^{1}\)H NMR spectra: the proton region of the lacidyl units (1), the methylene proton region of the glycolidyll (2), and carbonate units (3). Generally, PLGA copolymers with L-LA are semi-crystalline with a clear endothermal event on the DSC curve indicating the phenomenon of melting [21]. In this study, the DSC curves did not reveal melting endotherms for all terpolymers (Figure 6 and Table 3), which may suggest an amorphous character of all the obtained terpolymers. This feature may ensure higher bioavailability compared to semi-crystalline material. This attribute was suggested in the previous study of P(LA:GA:TMC) terpolymers releasing 17-\(\beta\)-estradiol and aripiprazole [13; 22]. In the case of PLGA copolymers, the value of the \(M_{n}\) is an important parameter to tailor the release profile of drug substances [18]. Generally, a lower \(M_{n}\) increases hydrophilicity, faster \(WU\) and degradation. Therefore, this study aimed to design rods with ARP based on terpolymers with various \(M_{n}\) values, _i.e._, 21 kDa, 59 kDa, and 77 kDa. It should be pointed out that an appropriately higher \(M_{n}\) value of terpolymers based on d.l-LA, L-LA, GA, and TMC is difficult to obtain. Therefore, in this study, Zr(Acac)\({}_{4}\) was proposed as a polymerization initiator providing the possibility of synthesizing polymers with a higher \(M_{n}\) than can be obtained with the commonly used tin(II) 2-ethylhexanoate (Sn(Oct)\({}_{2}\)). Generally, increasing the amount of monomers relative to the amount of initiator results in an increase in the \(M_{n}\)[25]. In this study, terpolymers with a \(M_{n}\) of 21 kDa, 59 kDa, and 77 kDa were synthesized with initiator/monomer ratios of 1:600, 1:1000, and 1:1200, respectively (Table 3). Moreover, Zr(Acac)\({}_{4}\) is less toxic than Sn(Oct)\({}_{2}\), which was shown previously [25]. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & \multirow{2}{*}{
\begin{tabular}{c} **\(\mathbf{F}_{LL}\)** \\ **(mol\%)** \\ \end{tabular} } & \(\mathbf{F}_{GG}\) & \(\mathbf{F}_{TMC}\) & \(\mathbf{T}_{m}\) & \(\mathbf{\Delta H}\) & \(\mathbf{T}_{g}\) & \(\mathbf{M}_{n}\) & \\  & & **(mol\%)** & **(mol\%)** & **(mol\%)** & **(c\({}^{\circ}\)C)** & **(J/g)** & **(c\({}^{\circ}\)C)** & **(kDa)** & **D** \\ \hline \multirow{4}{*}{Td,l 21} & Raw & 65.4 & 14.7 & 19.9 & \(ND\) & \(ND\) & 36.3 & 21.4 & 1.970 \\  & Rod & 63.9 & 15.7 & 20.4 & \(ND\) & \(ND\) & 35.1 & 20.4 & 2.030 \\  & rod-ARP & 63.5 & 15.9 & 20.6 & 128.7 & 8.4 & 33.7 & 18.7 & 1.998 \\  & Raw & 64.9 & 16.2 & 18.9 & \(ND\) & \(ND\) & 46.7 & 59.4 & 1.950 \\ \cline{1-1}  & Rod & 64.9 & 16.2 & 18.9 & \(ND\) & \(ND\) & 44.1 & 57.7 & 1.604 \\  & rod-ARP & 65.4 & 16.3 & 18.3 & 133.4 & 5.2 & 41.8 & 55.2 & 2.012 \\ \cline{1-1}  & Raw & 57.1 & 18.3 & 24.6 & \(ND\) & \(ND\) & 39.9 & 76.8 & 2.001 \\ \cline{1-1}  & Rod & 56.2 & 18.3 & 25.5 & \(ND\) & \(ND\) & 37.3 & 46.8 & 2.301 \\ \cline{1-1}  & rod-ARP & 56.2 & 18.3 & 25.5 & 133.6 & 3.4 & 37.4 & 43.9 & 1.928 \\ \hline \hline \end{tabular}
\end{table}