Vinyl alcohol copolymers for use in aqueous dispersions and melt extruded articles

1. In a method of preparing an aqueous dispersion selected from drilling fluids, hydraulic cement compositions, mineral pigment containing coatings, and papermaking furnishes, the improvement comprising: a) producing a saponified copolymer of vinyl alcohol (VOH) and 2-acrylamido-2-methyl propane sulfonic acid or a salt of such acid (AMPS) by steps including continuously feeding with agitation, vinyl acetate monomer (VAM) and AMPS as comonomers, a free radical yielding polymerization initiator, and a solvent for said comonomers, initiator, and copolymer resulting from the copolymerization of said comonomers into a first reaction zone, maintaining the resulting reaction mass in said first reaction zone under polymerization conditions for a residence time sufficient for a major proportion of AMPS fed to said first reaction zone to polymerize, continuously feeding reaction mass from said first reaction zone with an additional supply of AMPS to a second reaction zone, maintaining the reaction mass in the second reaction zone for a residence time sufficient to polymerize a major proportion of the AMPS added to the second reaction zone, continuously withdrawing reaction mass from the second reaction zone, separating copolymer of VAM and AMPS from the latter reaction mass, and saponifying by hydrolysis and/or alcoholysis a major proportion of the acetate groups in said copolymer to form a saponified copolymer of VOH and AMPS; and b) incorporating the saponified copolymer into the aqueous dispersion, wherein the AMPS is fed continuously to the second reaction zone such that the compositional drift of AMPS in the resulting copolymer results in the saponified copolymer having low compositional drift with regard to variations in the content of AMPS in the saponified copolymer as determined by C 13 NMR, as compared to the compositional drift with regard to variations in the content of AMPS in a comparative saponified copolymer of VOH and AMPS produced via a batch process.

2. The process of claim 1 , wherein the total amount of AMPS fed to both reaction zones is about 1 to about 20 wt. % based on the total of VAM and AMPS being fed.

3. The process of claim 1 , wherein the effluent from said second reaction zone has an actual polymer solids content of about 40 to about 85% and the percent conversion calculated from said actual polymer solids content and the theoretical polymer solids content equal to the amount of monomers added to the system is about 70 to about 99%.

4. The process of claim 1 , wherein the relative molecular weight of the VAM/AMPS copolymer obtained from the second reaction zone is indicated by a viscosity of a 15 wt. % solution of the copolymer in methanol of about 4 to about 30 cps.

5. The process of claim 1 , wherein the saponified copolymer of VOH and AMPS contains about 1 to about 8 mol % of polymerized AMPS (poly AMPS), about 1 to about 20 mol % of polymerized VAM (PVAc) and about 75 to about 98 mol % of polymerized VOH (PVOH), a degree of hydrolysis of about 70 to at least 99% indicated by C 13 NMR and a relative molecular weight indicated by a viscosity of a 4% aqueous solution of the VOH copolymer of about 3 to about 30 cps.

6. In a method of preparing a drilling fluid aqueous dispersion, the improvement comprising: a) producing a saponified copolymer of vinyl alcohol (VOH) and 2-acrylamido-2-methyl propane sulfonic acid or a salt of such acid (AMPS) by steps including continuously feeding with agitation, vinyl acetate monomer (VAM) and AMPS as comonomers, a free radical yielding polymerization initiator, and a solvent for said comonomers, initiator, and copolymer resulting from the copolymerization of said comonomers into a first reaction zone, maintaining the resulting reaction mass in said first reaction zone under polymerization conditions for a residence time sufficient for a major proportion of AMPS fed to said first reaction zone to polymerize, continuously feeding reaction mass from said first reaction zone with an additional supply of AMPS to a second reaction zone, maintaining the reaction mass in the second reaction zone for a residence time sufficient to polymerize a major proportion of the AMPS added to the second reaction zone, continuously withdrawing reaction mass from the second reaction zone, separating copolymer of VAM and AMPS from the latter reaction mass, and saponifying by hydrolysis and/or alcoholysis a major proportion of the acetate groups in said copolymer to form a saponified copolymer of VOH and AMPS; and b) incorporating the saponified copolymer into the aqueous dispersion, wherein the AMPS is fed continuously to the second reaction zone such that the compositional drift of AMPS in the resulting copolymer results in the saponified copolymer having low compositional drift with regard to variations in the content of AMPS in the saponified copolymer as determined by C 13 NMR, as compared to the compositional drift with regard to variations in the content of AMPS in a comparative saponified copolymer of VOH and AMPS produced via a batch process.

7. In a method of preparing an aqueous dispersion selected from drilling fluids, hydraulic cement compositions, and pigment coatings including a clay, the improvement comprising: a) preparing a saponified vinyl alcohol resin provided with sulfonic acid functionality by polymerizing vinyl acetate monomer (VAM) and an unsaturated sulfonic acid containing comonomer to produce a copolymer, followed by saponifying by hydrolysis and/or alcoholysis a major proportion of the acetate groups in said copolymer to form a saponified polyvinyl alcohol resin of vinyl alcohol VOH and the sulfonic acid containing comonomer, wherein the saponified polyvinyl alcohol resin consists essentially of recurring units I, II and III,

R 1 is present or absent and if present is C 1 -C 20 alkylene, C 4 -C 8 cycloalkylene, C 4 -C 8 heterocycloalkylene, arylene, heteroarylene, or —C(═O)—NH—R 2 is; R 2 is C 1 -C 10 alkylene, C 4 -C 8 cycloalkylene, C 4 -C 8 heterocycloalkylene, arylene, alkylarylene, heteroarylene, alkylheteroarylene; M is a cationic counterion or hydrogen; and wherein recurring unit I is present in the saponified resin in an amount of from about 0.5 to about 10 mole percent; recurring unit II is present in the resin in an amount of from about 75 to about 98 mole percent and recurring unit III is present in an amount of from about 1 to about 20 mole percent, and wherein the saponified polyvinyl alcohol resin is prepared by steps including continuously feeding with agitation, VAM, the unsaturated sulfonic acid containing comonomer, a free radical yielding polymerization initiator, and a solvent for said comonomers, initiator, and copolymer resulting from the copolymerization of said comonomers into a first reaction zone, maintaining the resulting reaction mass in the first reaction zone under polymerization conditions for a residence time sufficient for a major proportion of the unsaturated sulfonic acid containing comonomer fed to said first reaction zone to polymerize, continuously feeding reaction mass from said first reaction zone with an additional supply of the unsaturated sulfonic acid containing comonomer to a second reaction zone, maintaining the reaction mass in the second reaction zone for a residence time sufficient to polymerize a major proportion of the unsaturated sulfonic acid containing comonomer added to the second reaction zone, continuously withdrawing reaction mass from the second reaction zone, separating copolymer of VAM and the unsaturated sulfonic acid containing comonomer from the latter reaction mass, and saponifying by hydrolysis and/or alcoholysis a major proportion of the acetate groups in said copolymer to form the saponified polyvinyl alcohol resin; and

b) incorporating the saponified polyvinyl alcohol resin into the aqueous dispersion, wherein the unsaturated sulfonic acid containing comonomer is fed continuously to the second reaction zone such that tho compositional drift of the unsaturated sulfonic acid containing comonomer in the resulting copolymer results in the saponified copolymer having low compositional drift with regard to variations in the content of the unsaturated sulfonic acid containing comonomer in the saponified polyvinyl alcohol resin as determined by C 13 NMR, as compared to the compositional drift with regard to variations in the content of the unsaturated sulfonic acid containing comonomer in a comparative saponified polyvinyl alcohol resin produced via a batch process.

8. The improvement according to claim 7 , wherein the saponified polyvinyl alcohol resin consists essentially of the following recurring units:

9. The improvement according to claim 7 , wherein the saponified polyvinyl alcohol resin consists essentially of the following recurring units:

10. The improvement according to claim 7 , wherein the saponified polyvinyl alcohol resin consists essentially of the following recurring units:

11. The improvement according to claim 7 , wherein the aqueous dispersion is a drilling fluid.