Sulfur-containing poly (unsaturated carboxylic acid) and its uses and production process

A detergent builder, which comprises a sulfur-containing poly(unsaturated carboxylic acid), wherein the sulfur-containing poly(unsaturated carboxylic acid) comprises:

• a weight-average molecular weight (Mw) of 700 to 2500 and a molecular weight distribution (Mw/Mn) of not more than 2.5;
• with the sulfur-containing poly(unsaturated carboxylic acid) comprising a molecular end and sulfur bound to said molecular end in a form of a sulfonic acid group, and with the sulfur-containing poly (unsaturated carboxylic acid) being water-soluble;
• wherein a mixing ratio of (meth)acrylic acid in a monomer component is in the range of 90 to 100 mol % relative to an entire monomer component for the sulfur-containing poly(unsaturated carboxylic acid);
• wherein the sulfur-containing poly(unsaturated carboxylic acid) is obtained by polymerizing an unsaturated carboxylic acid in the presence of a combination of at least one persulfate and at least one bisulfite as a polymerization initiator;
• and
• wherein the polymerization initiator is adjusted in such a manner that:
• the total amount of the polymerization initiator as used is not smaller than 10 g equivalents per 1 mol of the unsaturated carboxylic acid as used, and the amount of the bisulfite accounts for not smaller than 8 g equivalents of the total amount of the polymerization initiator as used;
• and the polymerization temperature is controlled so as to be in the range of 25 to 90 ° C.;
• wherein the sulfur-containing poly(unsaturated carboxylic acid) is further obtained by polymerizing the unsaturated carboxylic acid in the presence of a heavy metal ion, wherein a content of the heavy metal ion is in a range of 0.1 to 10 ppm relative to the total weight of a polymerization reaction liquid when polymerization has been completed;
• wherein the bisulfite or its solution and the unsaturated carboxylic acid or its solution are dropwise added during polymerization, and a dropwise addition time of the bisulfite or its solution is completed earlier than completion of a dropwise addition of the unsaturated carboxylic acid or its solution by 1 to 30 minutes;
• and
• wherein said sulfur-containing poly(unsaturated carboxylic acid) comprises a sodium salt of poly(acrylic acid) having a sulfonic acid end group.