Esters of dicarboxylic acids and oxyethylated alcohols are an important class of plasticizers. Plasticizers based on them are considered environmentally friendly. Plasticization remains the key method of PVC modification. Studying the process of processing PVC into materials by melting requires knowledge of the relationship between the process parameters and the properties of the flow. For this purpose, measurement of rheological properties using the melt fluidity index is widely used. Two esters butylbutoxyethyladipate and decylbutoxyethyladipate were synthesized and their properties were investigated. Evaluation of the effect of the ether structure on intermolecular interactions and the magnitude of the energy barrier of the transition state revealed a clear dependence of the properties on the length of the alkyl radical. Thus, the introduction of BBEA reduces the viscosity of the PVC melt by 30-50% compared to DOF, for example, at 190 °C and 50 wt. The MFI of a PVC composition with a BBEA content is 7.0 g/10 min versus 1.4 g/10 min for a composition with DOP. There is a pronounced temperature dependence of viscosity for compositions with BBEA, as a result of the high mobility of PVC chains in its presence and the thermodynamic stability of the mixture, and a less pronounced dependence using DBEA due to limited conformational mobility. Compositions with BBEA retain their white color up to 195°C (at 50-70 wt.h.), which is associated with better homogenization and screening of labile chlorine-containing PVC groups. When using plasticizers, an enthalpy-entropy compensation effect was revealed: high ΔH values of the viscous flow of PVC melts are accompanied by less negative ΔS. The Gibbs energy (ΔG) remains stable (1.85–2.15 kJ/g), confirming the universality of the flow mechanism. The concentration dependence of the thermodynamic parameters is to reduce Ea by 20-40% with an increase in the plasticizer content to 70 wt.h.