The invention relates to a device for synthesis of a polymer under separation of a gaseous substance. Said device comprises a reaction chamber (1), which has a top section (11), a middle section (12) and a bottom section (13), an inlet opening (2) which is arranged in the middle section (12), a first outlet opening (3) which is arranged in the bottom section (13), a second outlet opening (4) which is arranged in the top section (11), a first return opening (51), which is arranged in the bottom section (13), a second outlet opening (52), which is arranged under the top section (11), a distribution device (6), which is arranged between the top section (11) and the middle section (12), and a removal device (7) which is arranged to be movable along the top section (11). The invention further relates to a method for synthesis of a polymer which can be carried out in said device.