Terpolymers of maleic anhydride and their use as scale control agents

Claim 2

A polymeric agent comprising a terpolymer, its hydrolyzed form, and the alkali metal, amine and ammonium salts thereof, said terpolymer consisting essentially of 30 to 55 mole percent maleic anhydride, 30 to 65 mole percent acrylamide or methacrylamide and 5 to 15 mole percent third monomer selected from the group consisting of styrene, α-methyl styrene, alkyl acrylate or alkyl methacrylate having from one to eight carbon atoms in the alkyl group and 1-alkene having from four to ten carbon atoms, said terpolymer being characterized by a relative viscosity of about 1.02 to 1.10 in dimethyl sulfoxide at a concentration of 0.5 g. per deciliter, and by solubility of less than 0.10 g. per g. of solution (water) at ambient temperature.

Claim 3

A terpolymer of claim 1 wherein said third monomer is styrene.

Claim 4

A terpolymer of claim 1 consisting essentially of 35 to 50 mole percent maleic anhydride, 40 to 55 mole percent acrylamide and 5 to 15 mole percent styrene.

Claim 5

The terpolymer of claim 1 consisting essentially of 41 to 45 mole percent maleic anhydride, 45 to 49 mole percent acrylamide and 9 to 13 mole percent styrene.

Claim 6

A hydrolyzed form of a terpolymer of claim 1.

Claim 7

The hydrolyzed form of the terpolymer of claim 4.

Claim 8

An alkali metal and ammonium salts of a hydrolyzed terpolymer of claim 1.

Claim 9

The alkali metal and ammonium salts of a hydrolyzed terpolymer of claim 4.

Claim 10

A process for preparing a terpolymer of claim 1 which comprises: heating a mixture of said maleic anhydride and said acrylamide or methacrylamide in a chain transfer solvent mixture to at least 120° C., introducing from 2 to 20 weight percent free radical initiator and said third monomer and continuing to maintain said mixture at a temperature of at least about 120° C until polymerization is essentially complete, said chain transfer solvent mixture being from 15 to 85 weight percent aromatic solvent selected from the group consisting of mono and dialkyl substituted benzene having from 1 to 4 carbon atoms in each alkyl group and trialkyl substituted benzene having from 1 to 2 carbon atoms in each alkyl group, and from 15 to 85 weight percent ketone solvent selected from the group consisting of dialkyl ketone having from 1 to 5 carbon atoms in each alkyl group and cycloalkyl ketone having from 5 to 8 carbon atoms in the cycloalkyl group.

Claim 11

A process of claim 9 which includes the steps of isolating said terpolymer after polymerization and treating said terpolymer with water at a temperature below about 30° C. to remove unreacted monomer.

Claim 12

The process of claim 9 wherein the terpolymer consists essentially of 41 to 46 mole percent maleic anhydride, 45 to 49 mole percent acrylamide and 9 to 13 mole percent styrene.

Claim 13

The process of claim 9 wherein said chain transfer solvent mixture is composed of substantially equal amounts of xylene and methyl isobutyl ketone.