Production process for aqueous poly(acrylic acid) solutions by means of controlled radical polymerisation

摘要

Preparing aqueous solutions of homo- or co-polymers of acrylic acid, comprises: initially charging aqueous solution or dispersion of sulfur-containing assistant (H) in temperature-controllable reaction vessel; heating to the desired reaction temperature; continuously adding water-soluble initiator having azo groups for thermal polymerization; continuously adding acrylic acid or its salts and optionally further co-monomers (C) or an aqueous solution of the monomers; and deactivating assistant (H) bonded to acrylic acid homo- or copolymer formed. The assistant H is an unsymmetric molecule (I). Preparing aqueous solutions of homo- or co-polymers of acrylic acid by means of controlled free-radical polymerization of acrylic acid and optionally water soluble mono-ethylenically unsaturated comonomers (C) in an aqueous medium in the presence of a sulfur-containing assistant (H) for control of the reaction, comprises: initially charging an aqueous solution or dispersion of the sulfur-containing assistant (H) in a temperature-controllable reaction vessel; heating to the desired reaction temperature; continuously adding a water-soluble initiator having azo groups for the thermal polymerization, where the molar ratio of the total amount of the initiator (In) to the assistant [In]/[H] is 1:1-1:100; continuously adding acrylic acid or its salts and optionally further comonomers (C) or an aqueous solution of the monomers, where the molar ratio of the monomers to the assistant [monomers]/[H] is 5:1-150:1; and deactivating the assistant (H) bonded to the acrylic acid homo- or co-polymer formed, provided that the polymerization is conducted up to a conversion of at least 99%, and the total amount of the aqueous medium is used so that after the process has been performed the concentration of the homo- or co-polymer is 20-60 wt.% based on all constituents of the aqueous solution. The amount of acrylic acid is at least 80 wt.% based on the sum of all monomers together, the number-average molar mass M nof the homo- or co-polymer is 500-10000 g/mol, the polydispersity of the homo- or co-polymer M w/M nis less than 2, the concentration of the homo- or co-polymer is 20-60 wt.% based on all constituents of the aqueous solution, and the polymerization temperature is 20-100[deg] C. The assistant H is an unsymmetric molecule of formula (R 1-X-C(S)-S-CR 2n(COOR 3) m) (I). Either n, m : 1 or 2; or n+m : 3; X : O or S; R 1R1a, R1b or R1c; R1a : CH 3, C 2H 5, 1-propyl, 1-butyl or 2-methyl-1-propyl; R1b : R 3OOC-(CH 2) o; o : 1-4; R1c : R 4-[-O-CH 2-CH 2] k-; k : 1-10; R 2, R 4H or 1-4C alkyl; and R 3H, cation, CH 3or C 2H 5. Provided that not more than one R 2is H.