Process for the production of polyolefins in an autoclave reactor

A process for the production of ethylene polymers selected from the group consisting of homopolymers of low and medium density and copolymers of low and medium density, in an elongated autoclave reactor having several reaction zones operated at a pressure of 100 to 300 MPa and a temperature of 100 to 300.degree. C., in which process monomer in a supercritical state and liquid initiator are introduced into said reactor through several feed inlets distributed along the reactor length, characterized in that temperatures are measured continuously inside the autoclave reactor at specific points distributed along the reactor length, each of said measured temperatures is compared with a corresponding preset temperature and the detected deviation between each pair of preset and measured temperatures is used in regulating the amount of process monomer and liquid initiator fed into the autoclave through the feed inlets in order to minimize the temperature deviations.