Devolatilisation apparatus comprising at least one extruder which has: - a barrel and n barrel holes B n having the associated hole diameters D n where n is an integer, - one or more screws W n which can be driven so as to rotate and are in each case arranged concentrically in one of the barrel holes B n, have an axis of rotation A n and are equipped with treatment elements whose cross-sectional profile in the circumferential direction has - m relative maxima R m max n in respect of the radial dimension of the cross-sectional profile to the axis of rotation A n of the screw W n, where m is an integer from 1 to 8, - a maximum value R max n in respect of the radial dimension of the cross-sectional profile to the axis of rotation A n of the screw W n, where R max n fulfils: R max n <= (D n /2) - at least one feed zone, - one or more devolatilisation zones comprising in each case at least one devolatilisation opening which is suitable for discharge of volatile constituents from a polymer-containing medium from the extruder, - at least one discharge zone, characterized in that the extruder has screw elements SE having a pitch t as treatment elements, which are configured so that at least two of the following three conditions are met: S1) the cross-sectional profile has at least one relative maximum R m max n based on the radial dimension of the profile curve, for which: 0.430 D n > = R m max n < 0.485 D n, S2) 1.60 D n < t < 3.00 D n, S3) the cross-sectional profile of the respective screw element has no tangential angle β greater than 25° on the active flanks located at the front in the direction of rotation in the range of the radial dimension from 0.90 R max to R max, where the tangential angle β is defined as - the smaller of the two angles formed on drawing the tangents at any point on the cross-sectional profile of the treatment element at which the cross-sectional profile cannot be continually differentiated - and is 0° at any point on the cross-sectional profile of the treatment element at which the cross-sectional profile can always be differentiated. - a barrel and n barrel holes B n having the associated hole diameters D n where n is an integer, - one or more screws W n which can be driven so as to rotate and are in each case arranged concentrically in one of the barrel holes B n, have an axis of rotation A n and are equipped with treatment elements whose cross-sectional profile in the circumferential direction has - m relative maxima R m max n in respect of the radial dimension of the cross-sectional profile to the axis of rotation A n of the screw W n, where m is an integer from 1 to 8, - a maximum value R max n in respect of the radial dimension of the cross-sectional profile to the axis of rotation A n of the screw W n, where R max n fulfils: R max n <= (D n /2) - at least one feed zone, - one or more devolatilisation zones comprising in each case at least one devolatilisation opening which is suitable for discharge of volatile constituents from a polymer-containing medium from the extruder, - at least one discharge zone, S1) the cross-sectional profile has at least one relative maximum R m max n based on the radial dimension of the profile curve, for which: 0.430 D n > = R m max n < 0.485 D n, S2) 1.60 D n < t < 3.00 D n, S3) the cross-sectional profile of the respective screw element has no tangential angle β greater than 25° on the active flanks located at the front in the direction of rotation in the range of the radial dimension from 0.90 R max to R max, where the tangential angle β is defined as - the smaller of the two angles formed on drawing the tangents at any point on the cross-sectional profile of the treatment element at which the cross-sectional profile cannot be continually differentiated - and is 0° at any point on the cross-sectional profile of the treatment element at which the cross-sectional profile can always be differentiated. - the smaller of the two angles formed on drawing the tangents at any point on the cross-sectional profile of the treatment element at which the cross-sectional profile cannot be continually differentiated - and is 0° at any point on the cross-sectional profile of the treatment element at which the cross-sectional profile can always be differentiated.