Abstract Introduction:

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1 Abstract In this study microwave plasma initiated polymerization in aim of synthesize of desired polymer for the first time was experienced. Ultrahigh molecular weight Sulfonated polyacrylamides (SPAM) were obtained by plasma-induced polymerization in water solutions. The influence of monomer concentration, initiation time and post polymerization period on polymer yield and intrinsic viscosity were investigated. Also optimum of intrinsic viscosity at time glow of 60s by altering power is evaluated at 150 w and reciprocally another optimum is calculated as 30s for glow discharge time at fixed power of 100 w as power of plasma. The TG result shows two stages of the weight loss. The first one occurred between 270 o C and 330 o C, with a weight loss about 45%, and the second one happened between 350 o C and 460 o C, with a weight loss about 25%. Fourier Transform Infrared spectroscopy (FTIR) and Hydrogen Nuclear Magnetic Resonance (H- NMR) spectroscopy results alongside all mentioned above indicate good properties which satisfy efficient viscosity modifiers in displacement of fluids and especially for our purpose, Enhanced Oil Recovery (EOR). Introduction: Recent Scientific researches show that the use of plasma initiated polymerization (PIP) has established as an advantageable method to produce free radicals in polymerization process. There are some systematic methods for routine polymerization such as: chemical, thermal, UV radiation, etc, while the positive point of this method compared with others is that it can obtain ultra high molecular weight polymers [1-4]. These polymers have a large number of applications in special industries, so the PIP method can address a vast variety of needs in industry.

2 Initially In 1979, Osada s research group applied plasma initiated polymerization for some special vinyl monomer and applied a radio-frequency generator for production of plasma [5-6]. However, this method could not achieve to huge success in industry, mainly because of a wide range of problems encountered in industry using RF plasma [7]. By way of illustration, in the former PIP method, which plasma was generated by radio frequency (RF) method, a low pressure about Torr is needed. This vacuum must be maintained for few days as post polymerization. In order to suppress the drawbacks of this method regard to sustainable development and economical concerns, we should use plasma generator system that could be applied in industry. In general, by employing the low pressure in the process of monomers degassing and the stage of glowing the plasma is necessary. However, the process of degassing can be carried out in pressure about 1 Torr. Moreover, Microwave (MW) generated plasma, glows easily at pressure about 1 Torr. Therefore, using the Microwave (MW) generated plasma in the PIP method in pressure about 1 Torr, which can be achieved by the use of a Rotary pump, is more practical and economical. Also, the Microwave generator rather than RF generator has a lower cost and working with it, is easier. Consequently, in the present work as an innovation, it was tried to use the Microwave to generate the plasma for initiating the polymerization process. Polyacrylamide is one of the practical polymers in industry which can be produced by PIP method. One of the most, important applications of this polymer is in the oil industry, especially in Enhanced Oil Recovery (EOR) projects [8]. The chosen monomers for this study were acrylamide (AM, M1) and 2-acrylamido-2-methylpropanesulfonic acid (AMPS, M2). The AMPS monomer is well-known for its hydrolytic stability, high solubility in water and good thermal behavior [9-12]. As a consequence, MW generated plasma was used for plasma initiated

3 polymerization and the effects of microwave discharge power and plasma exposure time on intrinsic viscosity of synthesized copolymers were investigated. Experimental setup: Synthesis of the copolymers. The monomers of acrylamide(am) and 2- acrylamido-2- methylpropane sulfonic acid (AMPS) were purchased from Merck Co. Then the purification of monomers was performed by methanol. Different ratios of monomers were mixed which in this step the concentration of 5% wt comonomer in deionized water was provided. 20cc of the comonomers solution was poured in a Pyrex container tube (figure 1). After connecting the tube to the vacuum pump, it was placed within the liquid nitrogen to turn the comonomers frozen. Then, we vacuum the system to Torr and allow the monomer to melt. This process is known to the degassing of the system. Repeating the degassing process -3 to 4 times- ensures the removal of oxygen from the solution. Finally, we froze the solution and evacuated the system again (with pressure about which was provided by rotary pump). After that, the vacuum valve was closed. The monomers turn to melt slowly which in turn set the stage for raising the pressure of the monomer tube. On the verge of observing the pressure about 1torr, the monomer tube was placed in the field applicator of Microwave wave guide (Figure.1), and plasma was ignited. Other applied conditions are presented in table I. After turning off the plasma, the container tube must be put in a dark place and maintains its vacuum for several days which is so-called post polymerization step. In all the tests represented in this report, the post polymerization process lasted for 3 days. The obtained polymer gel was purified and dried by distilled water and pure methanol. In this stage, polymers were separated from remained monomers in

4 the container by the help of methanol. Meanwhile the percentage of polymer conversion was measured. Physical Tests. The FTIR and 1 H-NMR spectra of the copolymers were obtained as the physical test. In order to obtain FTIR spectrum, purified and dried powder of the polymer was mixed with potassium bromide (KBr ) and prepared pills of this mixture were put in the spectrometer device, Tensor27 model (Bruker Co). The 1 H- NMR spectra are obtained in deuterated water (D 2 O) solutions at 60 o C on a JEOL- C60HL spectrometer with an electromagnet at 300 MHz. Measurements of intrinsic viscosity ([η]). Intrinsic viscosity of different samples of synthesized copolymers (AM-co-AMPS) was measured in different conditions in a solvent of distilled water at a temperature of 25 o C by Lauda Proline PV15 viscometry device. Results and discussions Sulfonated polyacrylamide has especially synthesized which is very practical in Enhanced Oil Recovery industry. In order to identify produced polymer, FTIR and H-NMR spectrum was obtained. In addition, the conversion percentage in comparison with pervious PIP methods was satisfying. As a significant parameter, the viscosity of polymer was measured which in turn results in insurance of its high molecular weight. Consequently, with the investigation of polymer thermal behavior, we sure that the appropriate polymer for EOR applications is produced. Copolymer Characterization Fourier Transform Infrared Spectroscopy (FTIR): The transmission FTIR spectrum for copolymer (AM-co-AMPS) was presented in Figure 2. The spectrum show typical absorption bands as follows: N-H stretching at 3442 cm -1, C=O

5 stretching at 1655 cm -1, CH, CH 2 and CH 3 stretching interactions at 1547 cm -1 and 1454 cm -1, CH, CH 2 and CH 3 bending interactions at 2928 cm -1, So group 3 stretching at 1204,1117 and 1040 cm -1. Proton Nuclear Magnetic Resonance Spectroscopy( 1 H-NMR) In the H-NMR spectrum, the peak of 1.6 ppm region is atributted to the hydrogens of the CH3 groups of C (CH ), and the CH2 groups of 3 2 CH 2 So3. Additionally, the peak of 2.31 ppm region is related to the hydrogen of the CH group of the main polymer chain, and the peak of the 3.5 ppm region is related to the hydrogen groups of CH2 of the main polymer chain. Copolymerization Data: Copolymerization data obtained from 1 H-NMR spectra (Figure 3) were summarized in Table 2. In the above table, changing results of 3 parameters, included plasma exposure time, plasma power and monomers ratio in various tests are presented. These testes were implemented for 3 arbitrary points, and for every one of them these 3 parameters were measured. By and large, the conversion percentage which is obtained by Microwave Plasma Initiated Polymerization, in comparison with pervious PIP methods, shows considerably a higher conversion [13]. Plasma parameters and its effects on intrinsic viscosity: How plasma parameters affect on viscosity? In order to answer this question, plasma variation which has correlation with molecular weight was identified by several equations. Then the reaction of intrinsic viscosity in response to change of these variables was investigated.

6 Radicals are created by plasma emission on the interface of frozen monomers. Most of these radicals will terminate with each other and lose the ability of initiating polymerization except a very few radicals reach the surface of the frozen monomers which initiate the polymerization quickly and form a long chain polymer. The energetic electrons of plasma impact with the monomer interface by collision number N which causes free radical generation that can be calculated by the following equation: N v t S, (1) where ν is known as the molecular collision rate, t as the exposure time and S as the surface of frozen monomers interface under glow (irradiation). Then the molecular collision rate ν can be calculated by: ( v [ n kt 1 ) ] 4. (2) m ν depend on the absolute temperature (T), mass of gaseous molecules plasma (m) and molecular density of the gas (n 1 ). On the other hand the whole number due to the collision is as follows: N e N, (3) where α, is ionization factor, is equal to: plasma density n 1. (4) So, according to equations (1), (3) and (4) it can be concluded that the main parameters in the plasma controling the radical generation in the monomers surface are the plasma density and also the exposure time [14]. Needless to say, working pressure (gas pressure) is also important that here was kept constant at 1 Torr. Effect of plasma density can be investigated by changing plasma power. In general, plasma power is directly related to plasma density. Figure 4 shows that

7 increasing the discharge power at first increases the intrinsic viscosity of copolymers. But there is an optimum point which by raising the power beyond it, the intrinsic viscosity begins to decrease. At the beginning, growing the power results in increasing of generated radicals. Therefore, because of direct relation between numbers of collisions with polymerization rate, numbers of these free radicals at optimum point are enough that during three days of post polymerization, polymer chain could be reached to maximum in regard to its rate and growth condition which in this optimum condition molecular weight and subsequently viscosity are desired. After that by more increasing of the plasma power, number of free radicals surplus optimum one, and collision probability of these free radicals at the head of these polymer chains which cause to end polymerization, could be increased. In other words increasing power will cause decreasing desired viscosity. Another important parameter related to plasma generation is the exposure time, by increasing this parameter, number of collisions and accordingly free radical generation increase. This phenomenon has similar effect of plasma power on the viscosity, Figure 5 shows the effect of exposure time on the viscosity. The Thermal Behavior of copolymer: The thermogravimetric analysis (TGA) was carried out by Mettler device, Sdta 851 e model, to investigate the thermal behavior of copolymer. The TG curve (Figure. 6) shows two stages of the weight loss. The first one occurred between 270 o C and 330 o C, with a weight loss about 45%, and the second one happened between 350 o C and 460 o C, with a weight loss about 25%.

8 Conclusion From our experimentally data on the synthesis of SPAM by PIP, for the firstime it is illustrated that Microwave can be used as utile as other plasma generators and also by correlating several operational parameters and polymer properties, it is possible now to select the optimum reaction conditions for the process. Also both the physical test data and ThermoGravimetric results motivate a possible use of the obtained SPAM polymers in EOR which satisfy the most important demands for those applications where it is desirable for the polymer solutions such as: They are completely soluble in water; Their molecular weights are ultrahigh, achieving ultrahigh viscosity in dilute solutions; They are satisfactorily indicate a good thermal stability with respect to TG data Reference 1 Simionescu BC, Natansohn A, Leanca M, Ananiescu C, Simionescu CI (1980) Polym Bull 3: Simionescu BC, Leanca M, Ananiescu C, Simionescu CI (1980) Polym Bull 3:437 3 Simionescu BC, Natansohn A, Leanca M, Ananiescu C, Simionescu CI (1981) Polym Bull 4:569 4 Simionescu CI, Simionescu BC, Ioan S, Leanca M, Chelaru C (1985) Rev Roum Chim (30) 6:441 5 D. R. Johnson, Y. Osada, A. T. Bell, M. Shen (1981) Macromolecules, 14, Y.Osada, A. T.Bell, SHEN M (1978) J. Polym. Sci., Polym. Lett. Ed C. Chelaru, I. Diaconu (2007) Polymer Bulletin 58,

9 8 Carmen Chelaru, I. Diaconu, C, I. Simionescu (1998) Polymer Bulletin 40, Cristofor I. Simionescu, Carmen Chelaru (1994) Polymer Bulletin 32, Dauben D L and Menzie D E (1967) J Pet Tech Aug: Heilweil I J and Hoskin (1986) U S Pat 4,619, Anupom Sabhapondit, Arun Borthakur, Inamul Haque (2003) Energy & Fuels, 17, Cristofor I. Simionescu, Bogdan C. Simionescu (1984) Pure & Appi. Chem. 56, YOU Qingliang, WANG Jianhua, M. ENG Yuedong, SHU Xingsheng, OU Qiongrong, XU Xu, SHEN Keming, (2006) Plasma Science & Technology, vo1.8, No.3,

10 Fig. 1.Microwave reactor. Fig. 2. FTIR spectrum of AM-co-AMPS.

11 intrinsic viscosity (dl/g) Fig 3. 1H-NMR spectrum of AM-co-AMPS discharge time: 60s feed composition: 3 (M1/M2) discharge power (W) Fig. 4. Discharge power effect on intrinsic viscosity.

12 intrinsic viscosity (dl/g) discharge power: 100W feed composition: 3 (M1/M2) discharge time (s) Fig 5. The glow discharge duration effect on intrinsic viscosity. Fig 6. TG and DTG curves of AM-co-AMPS: sample size mg, heating rate 10oC/min, nitrogen purge.

13 Various time(s) Various power(w) Various M1/M2** Table 1. Various parameters for copolymer. plasma exposure time (s) discharge power: 100w 15, 30, 60, 120 (s) feed composition (M1/M2):3/1 Discharge power (w) plasma exposure time: 60 s 50, 100, 150, 200, 300 (w) Feed composition (M1/M2): 3/1 Feed composition (M1/M2) 1/1, 3/1, 7/1 Discharge power:100w Plasma exposure time:60 s Table 2. copolymeization* data, percent of conversion and intrinsic viscosity for AM(M1)/AMPS(M2) copolymers obtained by PIP. Conversion (%) Copolymer d(m1)/d(m2)*** Intrinsic viscosity(dl/g) Power: 100W M1/M2: 3/1 30(s) 60(s) 120(s) Time: 60s 50(w) M1/M2: 3/1 100(w) (w) Power: 100W Time: 60s 7/1 3/1 1/ *from 1 H-NMR spectra. **for 5% wt monomer in water.***monomer ratio in the copolymer