000 preferably between 50 and 500 by separate feeding a molecular weight regulator can be conveyed to the reactor for example hydrogen or diethyl zinc optionally it can also be dispersed in paraffinic oil the amount of aliphatic aromatic or naphtenic solvent added of polymerization grade permits are to reduce the polymeric solution viscosity if the polymerization is carried out at temperatures greater than those critical of the most low boiling reactive monomers then the solvent must have a boiling temperature greater than the said critical temperature for example in the case of propylene the solvent must have a temperature greater than the critical temperature during the polymerization reaction the reaction is continuously fed ethylene and propylene or butene 1 or the desired alpha olefins or their mixtures to maintain a constant composition in the reactor this is accomplished through a chromatographic control of the gas phase of the reactor itself the polymer viscosity in the reactor is measured through a viscosimeter for example applied in parallel which gives the desired molecular weight of the polymer this last part is used to establish a priori the molecular weight of the polymer which is produced in the reaction the polymeric solution suspension coming from.