Patent ID: 8541518

Claim:
A process for preparing a copolymer in a semicontinuous mode of operation in a polymerization apparatus containing a polymerization reactor connected to a metering device, the process comprising: (a) initially introducing acid monomer into the metering device and initially introducing polyether macromonomer and water into the polymerization reactor, (b) metering the acid monomer from the metering device into the polymerization reactor, (c) passing free radical polymerization initiator into the polymerization reactor before and/or during the metering of the acid monomer into the polymerization reactor, wherein an aqueous medium forms in the polymerization reactor, and wherein the acid monomer and the polyether macromonomer are reacted in the aqueous medium by free radical polymerization forming the copolymer, at least 70 mol % of the polyether macromonomer initially introduced into the polymerization reactor being converted by the free radical polymerization, the conversion of the acid monomer produces in the copolymer an acid structural unit which reduces the pH of the aqueous medium less than does the acid monomer, wherein the metering of the acid monomer into the polymerization reactor first establishes an initial polymerization pH in the aqueous medium and then, until the conversion of 70 mol % of the polyether macromonomer initially introduced into the polymerization reactor, the metering of the acid monomer into the polymerization reactor at a metering rate that causes the pH in the aqueous medium to deviate by not more than ±0.3 from the initially established polymerization pH.