A mathematical algorithm that optimizes the reactor to produce the elastomeric copolyester copoly(ethylene-polyoxyethylene terephthalate), CEPT, is shown in this work. The optimization was carried out this way: First, an initial isothermal guess of temperature profile is made and the differential equations system, which describes the CEPT production process, is solved. Second, the reaction time is fixed and the objective function is calculated. Third, the adjoint variable equations system is solved and the Hamiltonian's function is calculated. Fourth, a new temperature profile is found by using the control vector iteration procedure. Finally, steps one to three are repeated until the objective function reaches a minimum value. The results of the optimization establish that the copolytransesterification reactor should be operated initially to high temperature (about 285 degreesC), which should be reduced quickly to near 250 degreesC to purposely diminish the production of by-products.