Abstract: A turbine mixer for a polyethylene reactor of the stirred autoclave type in which a turbine rotor is mounted on a rotating stirrer shaft extending along the longitudinal axis of the reactor and a turbine stator is mounted adjacent to and upstream of the rotor. The turbine mixer is positioned in the final stage of a three-stage, stirred autoclave reactor, and a baffle plate is positioned so as to extend across the reactor at the inlet to the final zone. The mixer produces intense stirring of the reactor materials within the final stage, but does not cause significant backmixing into the reactor zone immediately upstream thereof. The turbine mixer may also be utilized in other zones of the reactor wherein intense axial mixing of the reactor materials is required, in which case the baffle plate would be omitted so as to produce intensive axial mixing of the reactor materials within that zone.