Process for the preparation of polysulfones and polyethersulfones with reduced Yellowness Index

Process for the preparation of polysulfones a yellowness index to DIN 6167 of less than 19 and polyethersulfones a yellowness index to DIN 6167 of less than 30, wherein the polymerization is performed in basic solvents, aprotic using a stirrer positive and very little separation wall 5 with d / D> 0.9 transmission.