. The drying gas was nitrogen that comprises from 0% to 0% by volume of residual oxygen: Before start of polymerization the drying gas loop was filled with nitrogen until the residual oxygen was below 0% by volume. The gas velocity of the drying gas in the cylindrical part of the spray dryer (0) was 0.00 m/s. The pressure inside the spray dryer was 0 mbar below ambient pressure. The spray dryer outlet temperature was measured at three points around the circumference at the end of the cylindrical part as shown in FIG. 0. Three single measurements (00) were used to calculate the average cylindrical spray dryer outlet temperature. The drying gas loop was heated up and the dosage of monomer solution is started up. From this time the spray dryer outlet temperature was controlled to 000° C. by adjusting the gas inlet temperature via the heat exchanger (00). The 