## 3 Results and Discussion
However, PLGA plasticization is mentioned much more often in the literature. For PLGA copolymers, plasticization by PEG, ethyl pyruvate, ethyl salicate, methyl salicate, triacetin, and triethyl citrate has been described [57, 58]. During the hydrolytic degradation of PLGA, water also acts as a plasticizer [59]. It should be noted that the phenomena of plasticization and anti-plasticization may result from the concentration of plasticizers or drug substances. This issue has been described for mixtures of indomethacin and polymers such as Eudragit E PO, polyvinylpyrrolidone-vinyl acetate copolymer, polyvinylpyrrolidone K30, and poloxamer P188 [60]. In our study, the content of drug substance was low. Plasticizers increase polymer chain mobility, whereas anti-plasticizers cause the opposite effect. According to the chemical taxonomy, LTP belongs to the carboxylic ester derivatives of a fatty acid. It occurs in the liquid state and is viscous [61]. These features may decrease the polymer chain mobility and increase the \(T_{g}\). This effect did not result from the drug-polymer interaction because analysis of the first and second heating runs of P(l-LA:GA:TMC) matrix-LTP did not reveal additional endotherms and exotherms compared to the raw terpolymer (Tables 1 and 2). This is also reflected in the literature [62, 63]. Therefore, the observed \(T_{g}\) increase results rather from the rheological properties of LTP. It should be added that anti-plasticization may prolong polymer degradation and release patterns of drug substances. This is significantly important in the case of polymer-drug carriers with a relatively low \(T_{g}\). A noticeable decrease in the \(M_{n}\) was observed after solution casting in HFIP for P(l-LA:GA:TMC) matrix-LTP from 59.4 kDa to 42.2 kDa compared to the raw terpolymer (Tables 1 and 2). It should be noted that a comparable decrease, _i.e._, from 58.8 kDa to 41.1 kDa, was noted for a P(l-LA:GA:TMC) wafer with isperidone formulated by solution casting using methylene chloride [45]. In this study, the \({}^{1}\)H NMR measurements showed that solution casting did not significantly influence the composition of the terpolymer of P(l-LA:GA:TMC) matrix-LTP, which reflects previous studies [45, 64]. For the \(F_{LL}\) and \(F_{GG}\), the changes were observed from 64.7 mol% to 62.7 mol% and from 17.3 mol% to 19.4 mol%, respectively, which may result from the use of solvent and the dissolution process. No significant changes in the \(F_{TMC}\) were noted (Figure 1, Tables 1 and 2). The degradation of the P(l-LA:GA:TMC) matrix-LTP and EB-P(l-LA:GA:TMC) matrix-LTP revealed smooth changes in the unit distribution, which contributed to a steady and stable character of the degradation process. Initially, P(l-LA:GA:TMC) matrix-LTP contained a predominant \(F_{LL}\) (62.7 mol%), as well as lower \(F_{GG}\) and \(F_{TMC}\) (19.4 mol% and 17.9 mol%, respectively). A noticeable gradual increase in the \(F_{LL}\) and a decrease in the \(F_{GG}\) and \(F_{TMC}\) were observed during the 113 days of degradation to the final values equal to 69.9 mol%, 14.0 mol%, and 16.1 mol%, respectively. From the 43 rd day, a slight fluctuation in the values of all monomer contents was noted (Figure 1, Table 2). This observation reflects the previous degradation study on P(l-LA:GA:TMC) terpolymers, _i.e._, for rods with 17-\(\beta\)-estradiol or aripriprazole, a similar character of composition changes was obtained [40, 46, 65].