SUMMARY 1. INTRODUCTION. Keywords: Acrylamide; Cationic polyacrylamide; Ultraviolet initiation; Reactivity ratios; Sequence length distribution

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1 Determination of Reactivity Ratios of Copolymerization of Acrylamide (AM) and Methacryloxyethyltrimethyl Ammonium Chloride (DMC) with Ultraviolet Initiation, and Their Sequence Length Distribution Determination of Reactivity Ratios of Copolymerization of Acrylamide (AM) and Methacryloxyethyltrimethyl Ammonium Chloride (DMC) with Ultraviolet Initiation, and Their Sequence Length Distribution Yonghong Wang, Xinru Zhang, Wanjie Li*, Jialiang Cheng, Chengcen Liu and Jiajun Zheng College of Chemistry and Chemical Engineering, Taiyuan University of Technology, Taiyuan , China Received: 4 August 2014, Accepted: 18 February 2016 SUMMARY The copolymer P(AM-DMC), one kind of cationic polyacrylamide, was synthesized by using acrylamide (AM) and methacryloxyethyltrimethyl ammonium chloride (DMC) as monomers with ultraviolet initiation. The copolymer was characterized by Fourier transform infrared spectroscopy. The composition of the copolymer was determined from the chlorine content by silver nitrate titration. The effects of monomer feed ratio and conversion on the composition of copolymer were discussed. Reactivity ratios were determined by the Fineman-Ross, Kelen-Tudos and Yezrielev-Brokhina-Roskin methods, indicating that their positive order calculation results were very different with those of reverse order, when the reactivity ratios were determined by Fineman-Ross. However, their positive order and reverse order calculation results were similar when the reactivity ratios were determined by the Kelen-Tudos and Yezrielev-Brokhina-Roskin methods. Therefore, the reactivity ratios were determined using the average results of the Kelen-Tudos and Yezrielev-Brokhina-Roskin methods. The reactivity ratios of AM and DMC were and , respectively. This result showed that the copolymerization of AM and DMC was a non-ideal random copolymerization. Furthermore, the content of AM segments decreased with the increase of AM feed content, but the content of DMC segments increased. Moreover, the sequence length distribution was irregular and narrow, because AM was prone to homopolymerization. Keywords: Acrylamide; Cationic polyacrylamide; Ultraviolet initiation; Reactivity ratios; Sequence length distribution 1. INTRODUCTION Flocculation is an efficient and costeffective method for wastewater treatment, which is used in industry for fast solid-liquid separation 1-3. The particles in suspension have the same charges, which result in repelling each other so that they cause sedimentation of particles 4. By addition of flocculants, finely dispersed particles are aggregated together to form large flocs that settle more easily. The charge neutralization and polymer bridging effect are well recognized as one of the classical flocculation mechanisms in flocculent treatment *Corresponding author. Tel.: addresses: wangyonghong666@163.com (W. J. Li) Smithers Information Ltd., 2016 wastewater 5, 6. Polyacrylamide (PAM) and its copolymers with anionic and cationic monomers are important and widely used polyelectrolytes in industrial processes such as in waste water treatment as flocculent 7,8, which can lower the charge of particles and make them settle. The charge of particles in natural suspensions is almost always negative; thus cationic polyelectrolytes seem very effective flocculants. In addition, comparison of cationic PAM and anionic PAM in a new study demonstrates that cationic PAM forms more shear-resistant flocs than anionic PAM. Cationic polyacrylamide (CPAM), an important derivative of polyacrylamide, has a wide usage in industry. Methacryloxyethyltrimethylammonium chloride (DMC) and acrylamide (AM) can be easily polymerized by using free radical polymerization technique in aqueous solution 9,10. The unique structure of side chains and a high density of positive electric charges of P(AM-co-DMC) 11,12, a copolymer of AM and DMC, make P(AM-co-DMC) highly effective polymer flocculating agent. P(AM-co-DMC) can be used in the fields of water purification, papermaking, mining, household chemicals, printing, dyeing and oil production 13,14. Thus far, the most simple and widely used polymerization method for Polymers & Polymer Composites, Vol. 24, No. 5,

2 Yonghong Wang, Xinru Zhang, Wanjie Li, Jialiang Cheng, Chengcen Liu and Jiajun Zheng CPAM is solution polymerization. Solution polymerization can be initiated by heat, rays, microwave radiation, and ultraviolet (UV) light UV-initiated polymerization has a lower reaction temperature, less initiator, shorter polymerization time, faster reaction rate and higher molecular weight of polymer than other initiation systems 20,21. UV-initiated polymerization is also easy to operate and environmentally friendly 22,23. It is well known that physical properties are directly affected by the sequence length distribution, which is dependent on the reactivity ratios of both monomers. As a result, the reactivity ratios become an important parameter. However, up to now, little work was reported on determination of the reactivity ratios about copolymerization of AM and DMC with ultraviolet initiation. In this article, a cationic polyacrylamide flocculent was synthesized by the copolymerization of acrylamide (AM) and methacryloxyethyltrimethyl ammonium chloride (DMC) under ultraviolet (UV) radiation with 2, 2 -azobis(2-methylpropionamide) dihydrochloride (V-50) as photoinitiator. The structure of the copolymer was characterized by Fourier transform infrared spectroscopy. Reactivity ratios were determined by Fineman- Ross, Kelen-Tudos and Yezrielev- Brokhina-Roskin methods. The effects of monomer feed ratio and conversion on composition of copolymer were discussed. The sequence length distribution was discussed by analyzing the change of the content of sequence length. purchased from Guangchuangjing Import and Export Co. (Shanghai, China). 2, 2 -Azobis(2-methylpropionamide) dihydrochloride (V- 50) was obtained from Wako Pure Chemical Industries, Ltd. (Osaka, Japan) as a photo-initiator. The other chemicals (analytical pure grade) were obtained from Beijing Chemical Works (Beijing, China). All chemicals were used without further purification. All the water used in this experiment was deionized before use. 2.2 Preparations of P(AM- DMC) Mixtures of AM and DMC solution of different molar ratio was put into the reactor. The content of monomer in deionized water was less than 5%. Then, the reaction solution was bubbled with nitrogen gas for 30 min at room temperature to remove oxygen. Subsequently, V-50 was added. Finally, the reactor was exposed to radiation for 120 min with a 500W high-pressure mercury lamp (main radiation wavelength, 365 nm; average irradiation intensity between 300 and 400 nm, 5.6W cm -2, General Electric Company, USA) at ambient temperature. After radiation, the product was purified with ethanol three times, dried in a vacuum oven at 40 ºC for 24 h, and then weighed before calculating the conversion. The conversion was found to be less than 10%. The reaction route for the preparation of P(AM-DMC) is presented in Scheme 1. Scheme 1. Synthesis route of P (AM-DMC) 2.3 Measurement of Copolymer Composition The accurate determination of copolymer composition is of paramount importance to the accurate estimation of monomer reactivity ratios. The molar ratio of AM to DMC in the copolymers was determined by silver nitrate titration. The detailed way was as follows: 0.05 g of P(AM-DMC) was dissolved in 100 ml of deionized water into a 250 ml conical flask. The solution was titrated against 0.01 mol L -1 silver nitrate titration using potassium dichromate as the indicator. When the solution became white, the titration was completed. The molar ratio of MA to DMC in the copolymers was calculated by the following Equation 24 : (1) where ρ represents the molar ratio of AM to DMC in the copolymers; v represents the volume of silver nitrate consumption; c represents the molar concentration of silver nitrate; m represents the weight of P(AM-DMC); M 1 represents the molecular weight of AM; M 2 represents the molecular weight of DMC. 2.4 FTIR Characterization Fourier-transform infrared (FTIR) spectroscopic measurements of the samples were recorded 2. EXPERIMENTAL 2.1 Materials Acrylamide (AM), supplied from Changjiu Biochemistry (Jiangxi, China), was recrystallized from acetone before the experiment. Methacryloxyethyltrimethyl ammonium chloride (DMC) was 308 Polymers & Polymer Composites, Vol. 24, No. 5, 2016

3 Determination of Reactivity Ratios of Copolymerization of Acrylamide (AM) and Methacryloxyethyltrimethyl Ammonium Chloride (DMC) with Ultraviolet Initiation, and Their Sequence Length Distribution on a SHIMADZU FTIR-8400 spectrophotometer. The scanning wavenumber range of the experiment was cm -1 on transmittance mode with 30 scans at a resolution of 8.0 cm -1. For each sample, three scans were taken to identify the peaks. 3. RESULTS AND DISCUSSION 3.1 FTIR Spectra Figure 1 shows the FTIR spectra of PAM and P(AM-DMC), respectively. As shown in Figure 1(a), the characteristic absorption peaks at 3405 cm -1 and 3186 cm -1 are assigned to the -NH 2 - asymmetric and symmetric stretching vibration, respectively. The absorption peaks at 2941 cm -1 are attributed to the asymmetric stretching vibrations of CH 2 and CH 3, respectively. The absorption peak at 1665 cm -1 is assigned to stretching vibration of C-N in amide groups, and the absorption peak at 1455 cm -1 is attributed to deformation vibration of -CH 2 - groups 11. This demonstrated that PAM was obtained from AM homopolymerization. As shown in Figure 1(b), the peak at 1738 cm -1 is assigned to the stretching vibration of C=O in the ester groups of DMC. The absorption peak at 1163 cm -1 is attributed to the stretching vibration of C-O in the ester group. The peak at 953 cm -1 is assigned to the stretching vibration of N + (CH 3 ) 3 in DMC 13. The results from infrared spectral analysis indicated that the P(AM- DMC) was successfully prepared by copolymerization reaction of AM and DMC with ultraviolet initiation. (2) where G is defined as R (ρ-1)/ ρ; H is defined as R 2 /ρ; ρ represents the molar ratio of AM to DMC in the copolymer; R represents the molar ratio of AM to DMC in the feed; the slope of G vs H gives r l, which is the reactivity ratio of AM; whereas the intercept is -r 2, which is the reactivity ratio of DMC. If the R and ρ are defined as 1/R and 1/ρ, respectively, the Fineman-Ross equation (Eq. 2) is transformed into the reverse equation (Eq. 3), which is expressed as follows: (3) where the slope of G vs H gives -r l, which is the reactivity ratio of AM; whereas the intercept is r 2, which is the reactivity ratio of DMC. Figure 1. FTIR spectra of PAM (a) and P (AM-DMC) (b) Table 1 shows the Fineman-Ross method parameters of AM and DMC copolymerization. As shown in Table 1, the molar ratio of AM to DMC in the copolymer (ρ) decreased linearly with the decrease of the molar ratio of monomers in the feed (R). When R was reduced to from , the ρ was decreased to from This indicated that copolymerization activity of AM and DMC increased with the increase of monomers molar ratio in the feed, because the more monomers molar ratio in feed resulted in the more reactive radical. Figures 2, 3 show results of Fineman-Ross method for determination of reactivity ratios using positive order and reverse order, respectively. As shown in Figure 2, the reactivity ratio of AM and DMC were and using positive order method according to the linear fitting of parameters in Table 1, and 3.2 Determination of the Reactivity Ratios of the Copolymers The Fineman-Ross Method The Fineman-Ross equation (Eq. 2) is one of the simple methods to determine the reactivity ratios of the copolymers. The linear equation is expressed as follows 25 : Table 1. Fineman-Ross method parameters of AM and DMC copolymerization R ρ H G H G Polymers & Polymer Composites, Vol. 24, No. 5,

4 Yonghong Wang, Xinru Zhang, Wanjie Li, Jialiang Cheng, Chengcen Liu and Jiajun Zheng Figure 2. Fineman-Ross method plot for determination of reactivity ratios with positive order the linear correlation coefficient was As shown in Figure 3, the reactivity ratio of AM and DMC were and using reverse order method, and the linear correlation coefficient was Comparing the results of positive order and reverse order methods, they had considerable differences. Therefore, the Fineman- Ross method was unsuitable to determine the reactivity ratios of AM and DMC copolymerization The Kelen-Tudos and Yezrielev-Brokhina-Roskin Methods The Kelen-Tudos equation (Eq. 4) is one of the best methods to determine the reactivity ratios of copolymer, which can overcome disadvantages of the Fineman-Ross method. The linear equation is expressed as follows 26 : Figure 3. Fineman-Ross method plot for determination of reactivity ratios with reverse order (4) where G is defined as G/ (δ + H ); ζ is defined as H / (δ + H ); δ is defined as (H min H max ) 1/2 ; the slope and intercept of η vs ζ can obtain the reactivity ratios of AM and DMC, respectively. If R and ρ are defined as 1/R and 1/ρ, respectively, the Kelen-Tudos equation (Eq. 4) is transformed into the reverse equation (Eq. 5), which is expressed as follows: (5) Table 2. Kelen-Tudos method parameters of AM and DMC copolymerization G H η ζ η ζ where G is defined as G / (δ + H ); ζ is defined as H / (δ + H ); δ is defined as (H min H max ) 1/2 ; the slope and intercept of η vs ζ can obtain the reactivity ratios of AM and DMC, respectively. Table 2 shows the Kelen-Tudos method parameters of AM and DMC copolymerization. Figures 4, 5 show results of Kelen-Tudos method for determination of reactivity ratios using positive order and reverse order. As shown in Figure 4, the slope and 310 Polymers & Polymer Composites, Vol. 24, No. 5, 2016

5 Determination of Reactivity Ratios of Copolymerization of Acrylamide (AM) and Methacryloxyethyltrimethyl Ammonium Chloride (DMC) with Ultraviolet Initiation, and Their Sequence Length Distribution intercept were and respectively, according to linear fitting using the parameters of Table 2, and the linear correlation coefficient was The reactivity ratios of AM and DMC were and , respectively. As shown in Figure 5, the slope and intercept were and according to linear fitting using the parameters of Table 2, and the linear correlation coefficient was The reactivity ratios of AM and DMC were and , respectively. From the foregoing, the results of Kelen-Tudos method with positive and reverse order were close each other. Therefore, the Kelen-Tudos method was suitable to determine the reactivity ratios of AM and DMC copolymerization. Roskin methods had similar results. Therefore, the reactivity ratios of AM and DMC were averaged out from results of the Kelen-Tudos and the Yezrielev-Brokhina-Roskin methods. The ultimate reactivity ratios of AM and DMC were and , respectively. This demonstrated that AM was prone to homopolymerization, but DMC tended to copolymerize with AM, and it was difficult to observe homopolymerization. Therefore, when P(AM-DMC) was prepared with ultraviolet initiation using AM and DMC, DMC should be supplemented frequently to keep more reaction activity of copolymerization than homopolymerization. Figure 4. Kelen-Tudos method plot for determination of reactivity ratios with positive order The Yezrielev-Brokhina-Roskin method is another method to calculate reactivity ratios. It is obtained from Fineman-Ross method, which is multiplied by R -1 and ρ -1/2 on both sides of the equation. The least square method is used in this equation. The equation is expressed as follows 27 : (6) (7) Figure 5. Kelen-Tudos method plot for determination of reactivity ratios with reverse order where ; The reactivity ratios of AM and DMC were obtained from Eqs. 6 and 7 by the data of Table 1, and the n denoted the number of experiments. The reactivity ratios of AM and DMC were and , respectively. Comparing the results of the three methods, Kelen-Tudos and Yezrielev-Brokhina- Polymers & Polymer Composites, Vol. 24, No. 5,

6 Yonghong Wang, Xinru Zhang, Wanjie Li, Jialiang Cheng, Chengcen Liu and Jiajun Zheng 3.3 Composition of Copolymer at Different Feed Composition and Conversion The r 1 is more than 1, and r 2 is less than 1; r 1 r 2 is less than 1. It demonstrated that the copolymerization of AM and DMC was a non-ideal copolymerization without a constant ratio point. AM was more easily homopolymerized than copolymerized with DMC. Figure 6 shows the variation of AM composition in copolymer (F AM ) as a function of feed composition (f AM ). As shown in Figure 6, the curve of copolymerization was above the diagonal without a point of intersection. This illustrates that AM was easy to polymerize with itself and then become a homopolymer. Therefore, in practical production, more AM needed to be added to the polymerization system to maintain the initial feed composition because AM was used up firstly. Figure 6. Variation of copolymer composition as function of feed composition Figure 7. Variation of instantaneous composition of copolymer versus conversion with different initial feed composition. f 0 is AM feed composition; F is AM AM AM composition in copolymer Figure 7 shows variation of instantaneous composition of copolymer versus conversion. As shown in Figure 7, the instantaneous AM composition in copolymer increased with the initial molar ratio of monomer feed composition. In the initial stage, the instantaneous AM composition in the copolymer decreased gradually with the conversion at AM feed compositions from 0.4 to 0.8. Afterwards, the instantaneous AM composition in copolymer decreased sharply with increase of conversion. This illustrated that AM happened homopolymerization with the consumption of DMC, which resulted in lower AM compositions in the copolymer at high conversion. Figure 8 shows the variation of monomer composition and instantaneous composition of the copolymer versus conversion. The instantaneous composition of AM in the copolymer was always more than the AM feed composition during the copolymerization process. However, the instantaneous composition of DMC in copolymer was always less than the DMC feed composition. The instantaneous composition of AM in the copolymer decreased with the AM feed composition, but the instantaneous composition of DMC in the copolymer increased. The above analysis showed that AM was easier to undergo homopolymerization than copolymerization with DMC. As a result, a higher DMC feed composition resulted in a higher instantaneous composition of DMC. 3.4 Sequence Length Distribution of Copolymer at Different Monomer Ratios Figure 9 shows the sequence length distribution of P(AM-DMC). f 0 AM is the AM feed composition; X is the number of sequence length of AM or DMC unit; P is the probability of AM or DMC unit in P(AM-DMC). As shown in Figure 9, when the number sequence length was 1, 2, 3 and 4 at 0.2 of AM feed composition, the content of 312 Polymers & Polymer Composites, Vol. 24, No. 5, 2016

7 Determination of Reactivity Ratios of Copolymerization of Acrylamide (AM) and Methacryloxyethyltrimethyl Ammonium Chloride (DMC) with Ultraviolet Initiation, and Their Sequence Length Distribution Figure 8. Variation of monomer composition and instantaneous composition of copolymer versus conversion. f AM is the AM feed composition; F AM is the AM composition in copolymer; f DMC is the DMC feed composition; F DMC is the DMC composition in the copolymer AM sequences was 63%, 23%, 8.5% and 3% in P(AM-DMC), whereas the content of DMC sequences was 47%, 25%, 13% and 7%, respectively. This demonstrated that DMC was separated by AM in the copolymer uniformly. When the sequence length was 1, 2, 3 and 4 at 0.4 of AM feed composition, the content of AM sequences was 39%, 23%, 15% and 9%, whereas the content of DMC sequences was 70%, 21%, 6% and 2%, respectively. When the sequence length was 1, 2, 3 and 4 at 0.6 of AM feed composition, the content of AM was 22%, 17%, 13% and 10%, whereas the content of DMC was 84%, 13%, 2% and 0.3%, respectively. When the sequence length was 1, 2, 3 and 4 at 0.8 of AM feed composition, the content of AM was 10%, 9%, 7% and 7%, whereas the content of DMC Figure 9. Sequence length distribution of P(AM-DMC). f 0 is the AM feed composition; X is the number of sequence length AM of AM or DMC units; P is the probability of an AM or a DMC unit in P(AM-DMC) (a) (b) (c) (d) Polymers & Polymer Composites, Vol. 24, No. 5,

8 Yonghong Wang, Xinru Zhang, Wanjie Li, Jialiang Cheng, Chengcen Liu and Jiajun Zheng was 93%, 6.2%, 0.4% and 0.2%, respectively. The above sequence length distribution analysis indicated that the sequence length distribution of AM and DMC was narrow, and their segment was very short. Furthermore, the AM segment content decreased with the increase of AM feed content, whereas the DMC segment content increased. Moreover, it showed that the polymerization of AM and DMC was a non-ideal random copolymerization as a result of irregular sequence length distribution. 4. CONCLUSIONS The cationic flocculent, a copolymer of AM and DMC, was synthesized from acrylamide (AM) and a cationic monomer methacryloxyethyltrimethylammonium chloride (DMC), with ultraviolet initiation. The reactivity ratios of AM and DMC were and , as determined by the Fineman-Ross, Kelen-Tudos and Yezrielev-Brokhina-Roskin methods. The instantaneous composition of DMC in the copolymer was less than the DMC feed composition, and the instantaneous composition of monomer in the copolymer was closer to the feed composition with the increase of conversion. The copolymerization of AM and DMC was a non-ideal random process. The AM segment content decreased with the increase of AM feed content, whereas the DMC segment content increased, and the sequence length distribution was irregular and narrow, because AM was prone to homopolymerization. ACKNOWLEDGMENTS This work was financially supported by the National Natural Science Foundation (Grant No ), the Natural Science Foundation of Shanxi Province of China (No ), the Joint Fund of Shanxi Provincial Coal Seam Gas (No ), the Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi (No ), and the Foundation of Taiyuan University of Technology (No. 2015MS014). REFERENCES 1. Huang Y.F., Wu D.H., Wang X.D., Huang W., Lawless D. and Feng X.S., Sep. Purif. Technol., 158 (2016) Meraz K.A.S., Vargas S.M.P., Maldonado J.T.L., Bravo J.M.C., Guzman M.T.O. and Maldonado E.A.L., Chem. Eng. J., 284 (2016) Chen Z., Zhang W.J., Wang D.S., Ma T. and Bai R.Y., Water Res., 83 (2015) Mandik Y.I., Cheirsilp B., Boonsawang P. and Prasertsan P., Bioresour. Technol., 182 (2015) Ghernaout D. and Ghernaout B., Desalin. Water Treat., 44 (2012) Feng L.L., Kobayashi M. and Adachi Y., Colloid. Polym. Sci., 293 (2015) Duan J.C., Lu Q., Chen R.W., Duan Y.Q., Wang L.F., Gao L. and Pan S.Y., Carbohydr. Polym., 80 (2010) Zhu H.C., Zhang Y., Yang X.G., Shao L., Zhang X.M. and Yao J.M., Carbohydr. Polym., 135 (2016) Guan Q.Q., Zheng H.L., Zhai J., Zhao C., Zheng X.K., Tang X.M., Chen W. and Sun Y.J., Ind. Eng. Chem. Res., 53 (2014) Xu Q.H., Li W.G., Cheng Z.L., Yang G. and Qin M.H., Bioresources, 9 (2014) Abdollahi Z., Frounchi M. and Dadbin S., J. Ind. Eng. Chem., 17 (2011) Li X.Q., Yang T.T., Gao Q., Yuan J.J. and Cheng S.Y., J. Colloid Interface Sci., 338 (2009) Shen J.J., Ren L.L. and Zhuang Y. Y., J. Hazard. Mater., 136 (2006) Yang X.J. and Ni L., Chem. Eng. J., 209 (2012) Gonzalez G., de la Cal J.C. and Asua J.M., Chem. Eng. J., 162 (2010) Rani P., Mishra S. and Sen G., Carbohydr. Polym., 91 (2013) Zhu J.R., Zheng H.L., Jiang Z.Z., Zhang Z., Liu L.W., Sun Y.J. and Tshukudu T., Desalin. Water Treat., 51 (2013) Antunes E., Garcia F., Blanco A., Negro C. and Rasteiro M., Ind. Eng. Chem. Res., 54 (2015) Tang T. and Takasu A., RSC Adv., 5 (2015) Zhang G., Song I.Y., Ahn K.H., Park T. and Choi W., Macromolecules, 44 (2011) Zheng H.L., Ma J.Y., Zhu C.J., Zhang Z., Liu L.W., Sun Y.J. and Tang X.M., Sep. Purif. Technol., 123 (2014) Jachuck R.J.J. and Nekkanti V., Macromolecules, 41 (2008) Goodner M.D. and Bowman C.N., Chem. Eng. Sci., 57 (2002) Wang J.P., Chen Y.Z., Wang Y., Yuan S.J., Sheng G.P. and Yu H.Q., Rsc Adv., 2 (2012) Kelen T., Tüdöus F., Turcsányi B. and Kennedy J.P., J. Polym. Sci. Pol. Chem., 15 (1977) Arunbabu D., Sanga Z., Seenimeera K.M. and Jana T., Polym. Int., 58 (2009) Yang W., Xie D., Sheng X. and Zhang X., Ind. Eng. Chem. Res., 52 (2013) Polymers & Polymer Composites, Vol. 24, No. 5, 2016