A solution process for polymerizing one or more α-olefins of formula CH2═CHR, where R is H or an alkyl radical C1-12, to produce a polyolefin soluble in the reaction medium, the process comprising:a) polymerizing said one or more α-olefins in a solution phase in the presence of a polymerization catalyst and a inert solvent having a vapor pressure lower than 100 kPa at 20° C.;b) separating the produced polyolefin from the unreacted monomers and the inert solvent by means of a sequence of at least three volatilization chambers operating at a decreasing pressure, the second devolatilization chamber being operated at a pressure from 0.8 to 5 bar.