It has been experimentally confirmed that polyethylene terephthalate during its processing into products destruct without carrying out the process of solid-phase polycondensation. The conditions for both primary and secondary polyethylene terephthalate have been determined for carrying out the process of solid-phase polycondensation for its effective reaction extrusion with chain extenders. To confirm the effectiveness of the parameters of the solid-phase polycondensation process of polyethylene terephthalate, its reaction extrusion was carried out with commercially available chain extenders of the diepoxide class. The optimal content of chain extenders of the diepoxide class for changing the complex of physical, mechanical and rheological properties of polyethylene terephthalate modified by them was determined. It allows obtaining materials with an increased by 2.2 times characteristic viscosity.