The present invention relates to a process for the preparation of a copolymer in semicontinuous operation in a polymerization apparatus, comprising a polymerization reactor connected to a metering device, in each case acid monomer being initially taken in the metering device and polyether macromonomer and water in the polymerization reactor, acid monomer being metered from the metering device via an acid monomer metering line into the polymerization reactor, free radical polymerization initiator being passed into the polymerization reactor before and/or during the metering of the acid monomer into the polymerization reactor so that an aqueous medium in which acid monomer and polyether macromonomer are reacted with formation of the copolymer by free radical polymerization forms in the polymerization reactor, a portion of the copolymer-containing aqueous medium being passed continuously during the free radical polymerization from the polymerization reactor via a reaction mixture line which is connected via a mixing device to the acid monomer metering line, the discharged copolymer-containing aqueous medium being mixed with the acid monomer in the mixing device during the metering of the acid monomer and being recycled to the polymerization reactor after the mixing via the acid monomer metering line.