Process oils are used for rubbers to improve their flexibility and processability in industry. The solubility parameter is a convenient way to determine the solubility of materials. Inverse gas chromatography was used to calculate the solubility parameters and depict solubility spheres for distillated aromatic extract (DAE), treated distillate aromatic extract (TDAE), mildly extracted solvate (MES), and hydro processed naphthenic oil (NAP). Results showed that despite the similarity in values of the solubility parameters of DAE and TDAE at ambient temperature, increasing temperature led to a significant difference in values. In contrast to other oils, TDAE showed a better compatibility with polar solvents. In addition, the interaction parameters showed no specific dependence on the temperature for DAE, MES, and NAP, except for polar solvents and TDAE. DAE had the highest compatibility with aromatic solvents. Upon raising the temperature to values greater than 100 °C, the compatibility trend between oils and toluene was the same for all oils investigated, except for TDAE, which increased with increasing temperature whereas others showed a reduction. The increase in the alkyl chain was also effective in increasing the compatibility of the probes as well as their interaction parameter values. The solubility parameters (δ2) of process oils were determined to be 18.9, 18.9, 18.5, and 19.0 (J/cm3)0.5 for DAE, TDAE, NAP, and MES at 25 °C, respectively.

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