Maleic acid/(meth)acrylic acid copolymer

Claim 2

A process for producing an alkali metal salt of a copolymer of (1) maleic acid (MA) and (2) a vinyl carboxylic acid (AA) selected from the group consisting of acrylic acid and methacrylic acid, wherein the molar ratio (γ) of monomer units of (MA) to monomer units of (AA) in said copolymer is from 1.15 to 2.7, the number average molecular weight MW is from 1,000 to 8,000, and the product of (γ)×MW is at least 3,000, which comprises: gradually adding to (a) an aqueous solution of an alkali metal monomaleate having a pH of from 3.5 to 5.0, (b) said vinyl carboxylic acid or said acid which has been partly neutralized with an alkali metal neutralizing agent, and (c) a polymerization initiator effective to initiate copolymerization of said alkali metal monomaleate and said vinyl carboxylic acid, under conditions effective to copolymerize said vinyl carboxylic acid and said alkali metal monomaleate, the mol ratio of the total maleic acid monomer units to the total vinyl carboxylic acid monomer units added to said solution being in the range of from 1.2/1.0 to 3.0/1.0, and the solution being continuously maintained at a pH in the range of from 3.5 to 5.0 during the addition, whereby to form said copolymer.

Claim 3

A process for producing an alkali metal salt of a copolymer of (1) maleic acid (MA) and (2) a vinyl carboxylic acid (AA) selected from the group consisting of acrylic acid and methacrylic acid, wherein the molar ratio (γ) of monomer units of (MA) to monomer units of (AA) in said copolymer is from 1.15 to 2.7, the number average molecular weight MW is from 1,000 to 8,000, and the product of (γ)×MW is at least 3,000, which comprises: mixing an aqueous solution of (a) maleic acid, with (b) an alkali metal hydroxide, at a molar ratio (a)/(b) of from 1.00/1.00 to 1.00/1.15, to form an aqueous solution of an alkali metal monomaleate, said solution having a pH of from 3.5 to 5.0; then gradually adding to said solution (c) said vinyl carboxylic acid or said acid which has been partly neutralized with an alkali metal neutralizing agent, and (d) a polymerization initiator effective to initiate copolymerization of said alkali metal monomaleate and said vinyl carboxylic acid, said vinyl carboxylic acid and said polymerization initiator being added to said solution dropwise and separately from each other over a time period of from 5 to 10 hours, the polymerization being performed at a temperature of from 80° to 120° C., while continuously maintaining the pH of said solution in the range of from 3.5 to 5.0, the mol ratio of the total maleic acid monomer units to the total vinyl carboxylic acid monomer units added to said solution being in the range of from 1.2/1.0 to 3.0/1.0, whereby to form said copolymer in said solution.

Claim 4

A process for producing an alkali metal salt of a copolymer of (1) maleic acid (MA) and (2) a vinyl carboxylic acid (AA) selected from the group consisting of acrylic acid and methacrylic acid, wherein the molar ratio (γ) of monomer units of (MA) to monomer units of (AA) in said copolymer is from 1.15 to 2.7, the number average molecular weight MW is from 1,000 to 8,000, and the product of (γ)×MW is at least 3,000, which comprises: mixing an aqueous solution of (a) maleic acid, with (b) an alkali metal hydroxide, at a molar ratio (a)/(b) of from 1.00/1.00 to 1.00/1.15, to form an aqueous solution of an alkali metal monomaleate, said solution having a pH of from 3.5 to 5.0; then gradually adding to said solution (c) said vinyl carboxylic acid or said acid which has been partly neutralized with an alkali metal neutralizing agent, and (d) a polymerization initiator effective to initiate copolymerization of said alkali metal monomaleate and said vinyl carboxylic acid, said vinyl carboxylic acid and said polymerization initiator being added to said solution dropwise and separately from each other over a time period of from 5 to 10 hours, the polymerization being performed at a temperature of from 80° to 120° C., while continuously maintaining the pH of said solution in the range of from 3.5 to 5.0, the mol ratio of the total maleic acid monomer units to the total vinyl carboxylic acid monomer units added to said solution being in the range of from 1.2/1.0 to 3.0/1.0, whereby to form said copolymer in said solution.

Claim 5

A process as claimed in claim 1 or claim 2 wherein the pH of said solution is maintained in the range of from 3.8 to 4.5.

Claim 6

A process as claimed in claim 1 or claim 2 wherein said alkali metal is sodium.

Claim 7

A process as claimed in claim 1 or claim 2 in which, during the step of adding to said vinyl carboxylic acid and said polymerization initiator to said solution, an aqueous solution of an alkali metal hydroxide is added dropwise to said solution to maintain the pH of said solution in the range of from 3.5 to 5.0.

Claim 8

A process as claimed in claim 1 or claim 2 in which after said copolymer has been formed, an aqueous solution of an alkali metal hydroxide or an alkali metal carbonate is added to said solution to neutralize said copolymer.