Water-Soluble Copolymers. 67. Polyelectrolytes of N-Vinylformamide with Sodium 3-Acrylamido-3-methylbutanoate, Sodium 2-Acrylamido-2-methylpropanesulfonate, and Sodium Acrylate: Synthesis and Characterization Erich E. Kathmann, Leslie A. White, and Charles L. McCormick* Department of Polymer Science, University of Southern Mississippi, Southern Station, Box 10076, Hattiesburg, Mississippi 39406-0076 Received December 15, 1995; Revised Manuscript Received May 7, 1996 X ABSTRACT: Copolymers of N-vinylformamide (NVF) with sodium 3-acrylamido-3-methylbutanoate (NaAMBA), sodium 2-acrylamido-2-methylpropanesulfonate (NaAMPS), and sodium acrylate (NaA) were prepared by free-radical polymerization in aqueous solution using 2,2′-azobis(N,N′-dimethyleneisobu- tyramidine) dihydrochloride as the water-soluble azo initiator. Copolymer compositions were determined utilizing 13 C NMR by integration of the carbonyl resonances. Reactivity ratios were determined for NVF (M1)/NaAMBA (M2) (the BAVF series) and NVF (M1)/NaAMPS (M2) (the PSVF series). Both series, with r1 and r2 <1 and r1r2 < 0.075, are representative of copolymers that display alternating tendencies. Microstructural data calculated statistically by the methods of Igarashi support these findings. Weight- average molecular weights range from 0.9 × 10 6 to 7.5 × 10 6 and were determined by low-angle laser light scattering in 1 M NaCl solution. The findings are compared to previous results obtained for the copolymerization of acrylamide with the various anionic comonomers. Introduction Water-soluble and water-dispersible copolymers rep- resent one of the fastest growing classes of industrial products. The growth has been stimulated by the demand for environmentally compliant systems pre- pared in and processed from water. Applications in- clude water treatment, remediation, coatings and per- sonal care formulations, viscosity modification, and frictional drag reduction. 1-8 Although a large number of monomers are capable of polymerization into polymers with water solubility, only a few have sufficient water solubility and reactivity with appropriate comonomers to yield commercially viable systems. N-Vinylformamide (NVF), an isomer of acrylamide (AM), has recently received renewed atten- tion since purification procedures have been refined and high molecular weights are easily attainable. 9-18 In addition, the pendant formamide moiety of poly(NVF) is readily hydrolyzed to the corresponding amine. Both NVF and AM yield water-soluble homopolymers by free- radical polymerization; however, the structural differ- ences of the monomers significantly alter copolymeri- zation tendencies with various comonomers and micro- structural attributes. Knowledge of reactivity ratios of NVF and AM with specific comonomers, therefore, is an important factor in tailoring microstructure for desired rheological characteristics. Previous studies in our laboratories confirmed that NVF copolymerizes with electron-deficient monomers such as acrylamide and maleic anhydride to form copolymers with strongly alternating tendencies. 19,20 In this paper, we report the synthesis and molecular characterization of copolymers of NVF with sodium 3-acrylamido-3-methylbutanoate (NaAMBA), sodium 2-acrylamido-2-methylpropanesulfonate (NaAMPS), and sodium acrylate (NaA). The reactivity ratios for the copolymers with NaAMBA and NaAMPS were deter- mined by several methods and then used to statistically predict the microstructures of the resulting copolymers. Additionally, the molecular weight values were also determined by low-angle laser light scattering. These studies complement previous research in our laborato- ries on copolymers of acrylamide with the same comono- mer systems. 21-29 Experimental Section Materials. N-Vinylformamide (NVF) from Air Products and Chemicals Inc. was vacuum distilled prior to use (72 °C at 5 Torr). Acrylic acid from Aldrich Chemical Co. was vacuum distilled prior to use. 3-Acrylamido-3-methylbutanoic acid was synthesized via a Ritter reaction of equimolar amounts of 3,3- dimethylacrylic acid with acrylonitrile as reported by Hoke and Robins 30 and as modified by McCormick and Blackmon. 21,24 2-Acrylamido-2-methylpropanesulfonic acid from Aldrich Chemi- cal Co. was recrystallized from methanol and vacuum dried at room temperature. 2,2′-Azobis(N,N′-dimethyleneisobutyra- midine) dihydrochloride (VA-044) from Wako Chemicals USA, Inc., was used as received. Poly(N-vinylformamide-co-sodium 3-acrylamido-3- methylbutanoate) and Poly(N-vinylformamide-co-sodi- um 2-acrylamido-2-methylpropane sulfonate). The co- polymers of N-vinylformamide (NVF) and sodium 3-acrylamido- 3-methylbutanoate (NaAMBA), the BAVF series, and copoly- mers of N-vinylformamide (NVF) and sodium 3-acrylamido- 3-methylbutanoate (NaAMPS), the PSVF series, were pre- pared in an aqueous solution at 45 °C using 0.1 mol % of VA- 044 as the initiator. Each reaction was conducted in a 500 mL, three-necked flask equipped with a mechanical stirrer and a nitrogen inlet tube. A designated amount of either 3-acryl- amido-3-methylbutanoic acid or 2-acrylamido-2-methylpro- panesulfonic acid was added to a specific volume of deionized water. To this was added an equimolar amount of sodium hydroxide, and the pH of this mixture was adjusted to pH ) 8.5. Once the materials were completely dissolved, the ap- propriate amount of NVF was added and the mixture was then deaerated with oxygen-free nitrogen for 30 min and placed in a water bath at 45 °C. After the reaction mixture had equilibrated, VA-044 dissolved in 5 mL of deionized water was injected into the stirring solution. The total monomer con- centration was held constant at 0.5 M in each reaction. A low- X Abstract published in Advance ACS Abstracts, July 1, 1996. 5268 Macromolecules 1996, 29, 5268-5272 S0024 9297(95)01852 3 CCC $12 00 © 1996 A i Ch i lS it + +