Exptl. investigations of the thermal bulk polymn. of styrene (I) in pilot plants of different sizes were done. Each pilot plant consisted of a tubular recycle reactor connected in series with a tubular reactor, both completely filled with Sulzer motionless mixers. Kinetic, reactor, and viscosity models were verified at I conversions ?96%, temps. ?210 Deg, and polystyrene mol. wts. ?360,000. Scale-up studies were done which confirmed that multitubular reactors of special design could be applied for industrial polymn. processes. [on SciFinder (R)]