Micromixing in a tubular polymn. reactor is characterized by the mol. wt. of polystyrene obtained in the presence of a chain transfer agent. Monomer and the transfer agent are fed sep. into the reactor. For const. overall inlet concns., the mean mol. wt. produced is strongly dependent on mixing intensity. Expts. were carried out in a pilot plant loop tubular reactor of different configurations and monomer conversions ?80%. The degree of segregation as a function of energy dissipation and the characteristic reaction time can be described by an empirical correlation. It could be shown that the design of the mixer can change considerably the micromixing efficiency. [on SciFinder (R)]