| 摘要 |
Process for preparing an aqueous polymer dispersion by radical aqueous emulsion polymerisation of a mixture of monomers having at least one ethylenically unsaturated group, the mixture containing at least 30 wt. % in total mixture of monomers (A) containing two conjugated ethylenically unsaturated double bonds, comprises (a) dividing the monomer mixture into n portions, where n is at least 2; (b) introducing the first monomer portion into the polymerisation reactor together with dispersing agent, radical polymerisation initiator and aqueous dispersing medium and polymerising in a first stage commencing at a polymerisation starting temperature TP1 of 0 degrees C ≤ TP1 ≤ 50 degrees C such that the temperature of the polymerisation mixture rises by at least 20 degrees C to a highest value of TP1H without exceeding 80 degrees C, and then holding the temperature constant within the range TP1H to TP1H-10 degrees C until the conversion U1 of monomer to polymer is at least 60 but at most 90 mol %, after which the polymerisation mixture is cooled to a polymerisation starting temperature TP2 where TP2 = TP1 plus or minus 10 degrees C and 0 degrees C ≤ TP2 ≤ 50 degrees C; (c) adding the second monomer portion and polymerising the monomer mixture present in the reactor in the presence of the polymer already formed, the dispersing agent and the polymerisation initiator in a second polymerisation stage commencing at the polymerisation starting temperature TP2 such that the temperature of the polymerisation mixture rises by at least 20 degrees C to a highest value of TP2H without exceeding 80 degrees C, and then holding the temperature constant within the range TP2H to TP2H-10 degrees C until the conversion U2 of monomer to polymer is at least 60 but at most 90 mol %, after which the polymerisation mixture is cooled to a polymerisation starting temperature TP3 where TP3 = TP1 plus or minus 10 degrees C and 0 degrees C ≤ TP3 ≤ 50 degrees C; (d) adding and polymerising the remaining n-2 portions of the monomer mixture successively in the same way as the second portion and (e) after the nth polymerisation stage, optionally continuing the polymerisation at a temperature of 0-50 degrees C to a total conversion Utot of monomers introduced to polymer of at least 95mol. %. |
