Preparation of Ultra-High-Molecular-Weight Polyacrylamide by Vertical Solution Polymerization Technique Ekta Sonker, 1 Rudramani Tiwari, 1 Pubali Adhikary, 1 Krishna Kumar, 2 S. Krishnamoorthi 1 1 Department of Chemistry, Centre of Advanced Studies, Institute of Science, Banaras Hindu University, Varanasi, 221005, Uttar Pradesh, India 2 Applied Science Department, Madan Mohan Malaviya University of Technology, Gorakhpur, 273010, Uttar Pradesh, India A straightforward and novel methodology has been developed for the synthesis of ultra-high-molecular weight polyacryl- amide (PAM) by vertical solution polymerization technique. By varying the concentrations of acrylamide monomer, three dif- ferent grades of polymers (PAM-V 1 , PAM-V 2 , and PAM-V 3 ) have been synthesized and compared with the series of different grades of PAM (PAM-C 1 , PAM-C 2 , and PAM-C 3 ) synthesized through conventional solution polymerization technique. The synthesized grades PAM-V 1 , PAM-V 2 , PAM-V 3 , PAM-C 1 , PAM-C 2 , and PAM-C 3 have been characterized by 1 H NMR, infrared spectroscopy, intrinsic viscosity measurement, molecular weight determination by gel permeation chroma- tography, and thermal analysis. Rheological analysis has been carried out on the aqueous solutions of various grades of PAMs. Swelling behavior of ultra-high-molecular weight PAMs has also been investigated. The flocculation performances of all grades have been investigated in kaolin suspension by settling and jar test methods. POLYM. ENG. SCI., 00:000–000, 2019. © 2019 Society of Plastics Engineers INTRODUCTION Polyacrylamides (PAMs) find varied types of industrial appli- cations, such as in food, water treatment, paper, textiles, pharma- ceuticals, building products, environmental, detergents, oil field products, and mineral processing [1–7]. These polymers perform a variety of functions including uses as dispersing and suspending agents, stabilizers, thickeners, gellants, dewatering aids, floccu- lants, viscosity modifiers, film formers, binders, and lubricants. PAMs are organic substances that dissolve, disperse, or swell in water [8–12] and thus find widespread use in industrial processes such as in drinking and industrial wastewater treatment [13], oil sand tail- ings treatment [14], improvement of soil stability [15], and enhanced oil recovery [16]. During flocculation by PAM, polymer chains adsorb onto particle surfaces. Thus, finely dispersed particles aggregate to form large flocs. These settle readily easing the method of separation. With increasing polymer chain length (molecular weight), more parti- cles are involved, and as a result, flocculation improves [17]. That is why significant interests exist to synthesize high-molecular-weight PAMs as flocculants. In general, PAM can be synthesized by several methods, such as conventional solution [18], solid state [19], and microwave [20] polymerization reaction techniques to obtain polymer with required molecular weight. Through these methods, one can syn- thesize PAM with approximate molecular weight of 10 4 –10 5 Da. In our present work, we have first time reported the synthesis of ultra-high-molecular weight PAM (>10 8 Da) through vertical solution polymerization (VSP) technique using ceric ammonium nitrate (CAN) as an initiator [21]. In this technique, the initiator is injected from the bottom of the vertical column containing monomer solution and it travels upward against the gravitational force. The monomers are aligned longitudinally. Thus, the propagation step of polymeriza- tion is carried out in vertical direction. So, the method is named as VSP technique. Herein, the polymerization is carried out at room tem- perature, without N 2 purging and stirring. The present article also reports the swelling property of different grades of synthesized PAM in water at regular time intervals. Furthermore, this article reports the use of synthesized ultra-high-molecular weight PAM as flocculants for kaolin suspensions. All the experiments have been carried out repeatedly until the deviation is <0.1%. EXPERIMENTAL Materials Acrylamide, CAN, and acetone were supplied by S.D. Fine Chemicals, Mumbai (India). Kaolin was procured from E. Merck (India). All the chemicals were used as they were procured with- out further purification. Synthesis of PAM through VSP Technique In 25 mL of distilled water, 10 g of acrylamide was dissolved by constant stirring. The reaction mixture was poured into a vertical col- umn (40 cm height and 1.2 cm diameter), which was already sealed from the bottom by a rubber septum and vertically hanged with the help of column stand. Then 20 mg of CAN (dissolved in 1 mL of dis- tilled water) was injected into the solution through a hypodermic nee- dle from the bottom of the vertical column. The reaction mixture was left as such for 6 h at room temperature. The viscous polymer was then precipitated into 100 mL of acetone, filtered, and washed twice with acetone. The synthesized polymer was dried in oven at 50  C and then pulverized. Three grades of polymers were prepared by same method using different concentration of acrylamide monomer. The synthetic details of the different grades of polymers are given in Table 1. Synthesis of PAM through Conventional Solution Polymerization Technique In 25 mL of distilled water, 10 g of acrylamide was dissolved by constant stirring and nitrogen gas was passed through the solution for about 30 min. The reaction mixture was heated up to 60  C and the same temperature was maintained throughout the reaction time. Then 20 mg of CAN (dissolved in 1 mL distilled water) was injected into the solution through a hypodermic needle under N 2 gas purging. The reaction mixture was left on magnetic stirrer for 6 h, then the solution Correspondence to: S. Krishnamoorthi; e-mail: dr.skmoorthi@gmail.com DOI 10.1002/pen.25097 Published online in Wiley Online Library (wileyonlinelibrary.com). © 2019 Society of Plastics Engineers POLYMER ENGINEERING AND SCIENCE—2019