## 3 Results and Discussion
These insights highlight the importance of selecting appropriate ester structures for optimizing plasticizing effects in polymer formulations. Thus, in comparison with DOP, in order to achieve plastic of equal hardness, it is necessary to use 19% more DPEA; the amount of DBPA for a formulation of similar hardness is almost identical. Butoxy derivatives are characterized by greater effectiveness of plasticizing action in comparison with DOP and ensure the achievement of similar hardness at a lower dosage. The results obtained are comparable with the data on the plasticizing ability of succinic acid esters presented in [28]. The properties of plasticization have shown the importance of structure. Within the studied range, an increase in the total length of the molecules contributed to an improvement in plasticizing properties, while the addition of alkyl substituents to the middle part of succinic acid esters negatively affected the compatibility of plasticizers. Moreover, with an increase in the size of these substituents, the negative effect increased, which is associated with the ability of these compounds to rotate around the axis connecting the ester groups. According to the authors, a good compromise is digesyl succinate: the \(T_{g}\) index is comparable to that of the plasticizer DEHP. In another paper [35], the research results confirmed that the length of the side chain plays a more important role than the central structure [41] and that free rotation around alcohol substituents relative to the aliphatic chain of dicarboxylic acid plays an important role in the effectiveness of the plasticizer. The results were obtained by comparing the properties of plasticizers based on succinic and maleic acids with linear side chains in the C\({}_{4}\)-C\({}_{8}\) range. The structure of alcohol in the diester molecule has a huge effect on the plasticizing properties of esters. However, the branched structure of the alcohol group and the presence of an ethyl branch does not increase the mechanical characteristics of PVC compositions with an ester content. [PERSON], [PERSON] et al. [42] investigated a number of succinic acid esters and showed that succinates with longer alkoxy chains are as effective or more effective than DOP for plasticizing PVC in terms of percentage by weight. The incorporation of plasticizers into PVC formulations is crucial for modifying a polymer's structure and enhancing its properties [43]. This targeted alteration results in improved rheological and physico-mechanical characteristics, including strength, frost resistance, brittleness, hardness, melt flow index, toughness and overall manufacturability. Additionally, thermal and electrophysical properties are also positively impacted by these modifications. Research indicates that the manufacturability of PVC compositions is primarily evaluated through the rheology of the melts. A widely accepted method for assessing the recyclability of these polymers is through the measurement of the melt flow index (MFI). This critical indicator helps determine the appropriate temperature range for processing the polymer composition, ensuring optimal conditions for its application. Recent studies have demonstrated that the effectiveness of plasticizers is influenced by their chemical structure and their capacity for conformational changes, as well as their thermodynamic compatibility with the polymer matrix. For instance, different plasticizers exhibit varying degrees of compatibility with PVC, which directly affects their ability to enhance mechanical properties and processing behavior. The choice of plasticizer can significantly alter the fusion and rheological behavior of PVC compounds, impacting their final physical properties and usability in various applications. The influence of the structure and concentration of the developed dibutoxyethyl adipate, dibutoxypropyl adipate and diphenylethyl adipate on the flow temperatures of PVC compositions in comparison with the commercially available plasticizers DOP and DOA was studied (Figure 7).