ABSTRACT The effect of the reaction medium and process conditions on the modification of ground tire rubber (GTR) was studied. For this, a polar reaction medium (ethylene glycol) and a nonpolar medium (1‐octadecene) were compared, using hexadecylamine as a devulcanizing agent in a microwave reactor. The reactions were conducted, and those showing the most significant chemical and physicochemical changes related to devulcanization were selected for further detailed analysis. FTIR was used to confirm the modification of GTR, the reorganization of sulfur bonds, and changes in the main structure of the polymer. Additionally, thermal and physicochemical characterization techniques, such as differential scanning calorimetry (DSC), soluble fraction content, and crosslink density, were employed to connect devulcanization treatments with changes in the crosslinked network of the polymers. Finally, the morphology of both modified and unmodified GTR was examined using light and scanning electron microscopy, where the size of GTR particles was reduced by about 13%. A direct relationship was established between the power applied and the percentage of devulcanization achieved with the tire powder. The morphological study revealed surface degradation in particles treated at 200°C with 10 phr of amine, and all treated samples showed a tendency to form agglomerates. These changes were attributed to the surface modification of the powder caused by the treatments.