Inverse Emulsion Free-Radical Polymerization of Acrylamide Terpolymer for Enhanced Oil Recovery Application in Harsh Reservoir Conditions L. Garc  ıa-Uriostegui, 1 G. Pineda-Torres, 2 S. L  opez-Ram  ırez, 2 J. Barrag  an-Aroche, 2 C. Dur  an-Valencia 2 1 Centro Universitario de Ciencias Exactas e Ingenier  ıas, U de G, Guadalajara, Jalisco, C.P. 44430, M exico 2 Universidad Nacional Aut  onoma de M  exico, Facultad de Qu  ımica. Departamento de Ingenier  ıa Qu  ımica. Ciudad Universitaria, CDMX, C.P. 04510, M exico A free-radical inverse emulsion polymerization formula- tion has been developed for preparation of acrylamide (AAm)/sodium 2-acrylamido-2-methylpropanesulfonate (AMPSNa)/N-vinylpyrrolidone (VP) terpolymers. An aque- ous solution of a blend of monomers is emulsified in n- decane using Tween 85 (Tw85). Ammonium persulfate (APS) and dicumyl peroxide (DCP) were used as initiators for water and oil phases, respectively. The reactions were catalyzed by temperature and by a redox pair; the former is achieved at 608C and the latter by adding tetramethyle- thylenediamine (TEMED) and sodium bisulphite (BisNa) to activate the initiator in water and oil phase, respectively. The emulsion type, stability, conversion, and rate of poly- merization were analyzed. The obtained terpolymer was characterized by elemental analysis, infrared spectrosco- py (FTIR), 13 C nuclear magnetic resonance (NMR), ther- mogravimetric analysis (TGA), differential scanning calorimetry (DSC), gel permeation chromatography (GPC), and rheology. Thermal catalyzed emulsion polymerization initiated with DCP showed the best performance as vis- cosity control agent and as polymeric precursor for in situ gel forming, for water mobility control and flow diver- sification, respectively. Both application for enhanced oil recovery purposes in harsh oil reservoir conditions are presented. POLYM. ENG. SCI., 00:000–000, 2017. V C 2017 Society of Plastics Engineers INTRODUCTION Polyacrylamide (PAAm) and their heteropolymers are of great importance, because of their good thickening capability, flocculation, and rheological behavior [1]. Polymers based on acrylamide (AAm) and their derivatives are easily available and relatively economic; moreover, these water-soluble materials offer a unique combination of useful properties [2–5]. These materials are applied in oil fields as viscosity control agents [6], adhesives [7, 8], and flocculants [9]. The most relevant applica- tion of PAAm in the oil industry, involves its use as viscosity control agent and conformance control [10] to enhance oil recovery and water control in producer wells [11–13]. Applica- tions in harsh conditions have been reviewed by Wu et al. [14]. In their work, the performance of acrylamide based polymers was studied using brines with total dissolved solids (TDS) up to 180,000 ppm. Samples were aged for 6 months at 1208C in low oxygen environments. Improved stability was reported by intro- duction of co-monomers with improved resistance to the brine ions and the environmental conditions. Water control in produc- er wells is achieved by injecting brine solutions or “gelants” consisting of polymers and crosslinking agents. The crosslinking reaction is rapidly accelerated as the temperature is increased and subsequently an in situ gel is formed. Afterward, depending on the chemical composition of the crosslinked network and the chemical environment, a phenomena call “syneresis” occurs. Gel syneresis refers to the exclusion of solvent from its network originated by an excess of crosslinking agent [15, 16]. There- fore, mechanical properties of the in situ gel change drastically leading to brittle structures. There are several crosslinking agents coming from inorganic (Cr 31 ) and organic (phenol-form- aldehyde and polyethylenimine) sources, nevertheless, in the last decade, the use of less toxic crosslinking reagents such as polye- thylenimine has been extended [17]. The main methods for synthesizing AAm homo and copoly- mers are bulk, solution, suspension, and emulsion polymeriza- tions. With regard to solution polymerizations, it has been observed localized increases in viscosity during the course of the reaction. This fact, depending on the reacting conditions, may induce an auto-acceleration or Trommsdorff-Norrish effect. As an outcome during the later stages of conversion the termi- nation reaction diminishes while rapidly increasing the medium temperature, resulting in a gelatinous, and undesirable physically crosslinked polymer, which is difficult to dissolve and to manip- ulate in water [18]. However, there are other polymerization methods to control the synthesis of high molecular weight PAAm, maintaining high reaction rates, and a viable reactor operation at high monomer concentrations. Emulsion polymeri- zation is a practical method to prepare polymers, and it provides an excellent medium to remove the heat of reaction and to pro- duce viscosity-controlled polymers, which are easy to process. Furthermore, the polymers obtained by this method are applied directly to a wide variety of uses, such as: synthetic rubber, high impact polymers, latex foams, latex paints, paper coatings, and so forth [6, 19]. Inverse emulsion polymerization offers the same benefits as direct emulsion, for example, easier heat dissipation, lower bulk viscosity, and high molecular weight polymers without decreas- ing the polymerization rate [20, 21]. Inverse emulsion polymeri- zation has been used to obtain hydrophilic polymers as latex; the method consists of a mechanically dispersed aqueous mono- meric solution (disperse phase) in an organic solvent (continu- ous phase), which are stabilized with a surfactant to form droplets that act as multiple batch reactors. In this article, the synthesis of polyacrylamide (PAAm) copolymerized with AMPSNa and VP via inverse emulsion has been developed. Recently, industrial applications of AMPSNa have received Correspondence to: C. Dur an-Valencia; e-mail: cduran68@gmail.com DOI 10.1002/pen.24499 Published online in Wiley Online Library (wileyonlinelibrary.com). V C 2017 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2017