from the upper vapor phase portion within the reactor and passed into this condenser the monomer vapor is condensed and sub cooled to about 60 u00b0 f in the reflux condenser and is then returned to the reactor the rate of monomer vapor removal is adjusted so as to maintain the temperature in the reactor interior at desired reactor temperature e g about 327 u00b0 f and so as to maintain a desired pressure in the reactor e g about 21 psia the mixture of polystyrene and unreacted material withdrawn from the reactor is continuously pumped into a wiped film devolatilizer where all unreacted monomer except for about 1 percent based on total weight of polymer product is removed from the polymer the pressure in this devolatilizer is about 100 mm hg absolute the apparatus and control system used here are similar to those above described in reference to the system of fig1 excellent control of process variables is obtained the controls operate to compensate for substantially all process variations disturbances and to bring the process to the throughput rate and weight fraction of polymer in the reactor as initially prechosen the effect of changing the conditions from steady state and the ability of the present control system to govern the situation is illustrated by the plots comprising fig3 in fig3 part a shows the response of the percent polymer in the reactor part b shows the response of the reactor fillage part c shows the reactor effluent flow rate and part d shows the polymer product flow rate as a function of time when the unreacted material flow rate is increased from 54 pounds hour to 59 4 pounds hour and the styrene monomer feed flow rate is increased.