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Synthesis and characterization of chitosan grafted with polystyrene using ammonium persulfate initiator
Materials Letters 124 (2014) 12–14
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis and characterization of chitosan grafted with polystyrene using ammonium persulfate initiator Abdulganiyu Umar a, Ahmedy Abu Naim a,n, Mohd Marsin Sanagi b a b
Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia Ibnu Sina Institute for Fundamental Science Studies, Nanotechnology Research Alliance, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia
art ic l e i nf o
a b s t r a c t
Article history: Received 2 July 2013 Accepted 1 March 2014 Available online 11 March 2014
Graft copolymerization of styrene from chitosan was prepared under various conditions using ammonium persulfate (APS) initiator. The grafting was found to be best at 1:3 chitosan:styrene weight ratio, 0.4 g APS and temperature 60 1C. The washed products were characterized by spectroscopic and thermal methods. FT-IR analysis indicate the presence of polystyrene peaks, DSC analysis showed the improvement in Tg of the polystyrene. After acid hydrolysis, the copolymer was analyzed using gel permeation chromatography (GPC), and the result revealed the isolated polystyrene having Mw and Mn as 95,249 and 30,755 respectively, with polydispersity index, 2.92. & 2014 Elsevier B.V. All rights reserved.
Keywords: Chitosan Grafting Polystyrene Ammonium persulfate Free-radical polymerization
1. Introduction Chitosan is a deacetylated form of chitin having D-glucosamine repeating units linked by β (1-4) glycosidic bond. It is rigid and specific crystalline structure made it to exist in nature in different polymorphic forms having various properties [1]. As such its applications in both pharmaceutical and medical fields were exploited [2]. Its solubility in acidic media made it to have different applications as gels, solutions, films and fibres [3]. Chitosan is also used in food and textile industries, cosmetic, waste water treatment [4]. Chemical modification of biopolymers is an important aspect which continues to receive considerable attention. One of the applications is the formation of the graft copolymers via free radical mechanism. “Grafting onto” technique was employed to graft vinyl monomers onto chitosan using different initiators. Poly (N-vinyl imidazole) was grafted onto caboxymethyl chitosan using potassium persulfate initiator [5]. Acrylic acid was grafted onto chitosan using ammonium persulfate initiator [6]. 4-(6-methacryloxyhexyloxy)-4'-nitrobiphenyl grafted onto chitosan using AIBN as initiator [7]. Other groups used cerium ammonium nitrate as initiator [8,9]. Recently, N-vinyl-2-pyrrolidone was grafted onto chitosan using potassium bromate as initiator [10]. In the present study, we report the grafting of polystyrene from chitosan backbone using ammonium persulfate initiator. Because of the enhanced porosity gained by the addition of polystyrene,
n
Corresponding author. Tel.: þ 60 75534462; fax: þ60 75566162. E-mail address: [email protected] (A. Abu Naim).
http://dx.doi.org/10.1016/j.matlet.2014.03.007 0167-577X/& 2014 Elsevier B.V. All rights reserved.
the copolymer could be used effectively for the removal of dyes from aqueous solutions.
2. Materials and methods Chitosan (deacetylation degree 85%) and styrene were purchased from Sigma-Aldrich (St. Louis, USA), and the chitosan was used after dried in oven at 100 1C. Ammonium persulfate (APS), ethylbenzene from Acros (New Jersey, USA), methanol and chloroform from QRëc (Selangor, Malaysia). All the chemicals were used as received except styrene. Styrene was washed three times using 5% NaOH(aq) to remove the inhibitor, washed with deionized water, dried with calcium hydride (CaH2) and capped in a conical flask before use. Graft copolymerization was carried out at various reaction conditions. Chitosan solutions were prepared as described [11]. Chitosan (1 g) was dissolved in HCl(aq) (100 mL, 0.1 M) and stirred with glass rod to obtain homogenous solution. The solution was mixed with APS (0.2–1 g) in a flask, fitted with condenser, nitrogen atmosphere and stirred with magnetic bar for 40 minutes as preinteracting time. Styrene was added to the system. The reaction mixture was then heated at temperature range. The reaction was stopped by pouring the reaction mixture into methanol. The precipitate was filtered using sintered glass funnel, dried in vacuum oven at 40 1C. The crude products were washed (soxhlet extraction) for 48 h to remove any polystyrene present. The extracts were filtered and dried in vacuum oven at 50 1C. The graft product was hydrolyzed to isolate the polystyrene, by immersing the sample (1 g) in HCl (20 mL, 6 M) and stirred at 90 1C overnight. The acid
A. Umar et al. / Materials Letters 124 (2014) 12–14
was removed by simple filtration. Chloroform (30 mL) was poured onto the residue, concentrated under reduced pressure and poured into methanol to precipitate the polystyrene. Molecular weight of the isolated polystyrene was determined by gel permeation chromatography (GPC). The FT-IR spectrums of chitosan Fig. 3(a) and chitosan-g-PS Fig. 3(b) were recorded using Perkin Elmer Spectrumone spectrometer (Shelton, Connecticut, USA). The glass transition point of the graft copolymer was analyzed using Thermal Advantage Instrument Q2000 with Tzero technology having refrigerated cooling system (RCS 90), using aluminium pan under a 50 mL/min N2 flow at the heating rate of 20 1C/min on the second heating of a heating-cooling-heating cycle. A sample of approximately 11 mg was used. The samples were scanned in the temperature range 20–180 1C. The percentage grafting G(%), and yield of graft copolymerization, Y(%) were calculated according to the following equation [12]: Gð%Þ ¼
W2 W1 100 W1
ð1Þ
Yð%Þ ¼
W 2 W 1 100 W3
ð2Þ
where W1 represents weight of the chitosan, W2 represents weight of the copolymer and W3 represents weight of the styrene.
3. Results and discussion
that could promote early termination of the growing radical, which promote homopolymerization of styrene [16]. As evident from FT-IR, Fig. 2(b) indicates the presence of polystyrene peaks with IR band intensities at 3150–3000 cm 1 (C–H(aromatic)), 3000–2850 cm 1 (–C–H stretching (alkane)), 1660–1500 cm 1(C¼C aromatic) in addition to peaks due to chitosan at 3600–3200 cm 1(O–H and N–H stretching) and 1659 cm 1 due to C¼O stretching (Fig. 2a), indicating that polystyrene has successfully been grafted from chitosan. Another evidence of the graft copolymerization is, the increase in Tg to 106 1C, which was higher than the normal Tg of polystyrene (which is about 100 1C) as shown in Fig. 3, since chitosan does not possess Tg due to its rigid structure [17]. The graft copolymers were hydrolyzed with HCl(aq) as shown in Scheme 1(d). The IR spectra of the hydrolyzed product (Fig. 2(c)) resembles that of linear polystyrene, with terminal OH at 3400 cm 1. GPC analysis showed that the Mw, and Mn, of the isolated polystyrene were 95,249 and 30,755, respectively, with PDI of 2.92. The broad molecular weight distribution could be a result of non-uniform distribution of the side chains on the chitosan backbone due to slow decomposition of initiator or fast termination between growing radicals [18]. Table 1 Effect of chitosan:styrene ratio and temperature on the percentage of grafting, G(%), and yield of graft copolymerization, Y(%), of samples polymerized for 3 h with 0.1 M HCl (100 mL) and APS(0.4 g). a
Chitosan completely dissolved in 0.1 M HCl and formed a viscous solution. This could be due to high molecular weight of the polymer. Graft copolymerization was carried out in a heterogeneous phase with styrene monomer (Scheme 1). Macroradicals were generated on the chitosan backbone by adding APS. Various reaction conditions were chosen to optimize G(%) and Y(%). Grafting was carried out at different temperatures, (50–80 1C) and at 1:3, 1:1 and 3:1 chitosan:styrene weight ratio; while the APS content and reaction time were kept constant (Table 1). It was observed that the percentage grafting, G(%) and percentage yield, Y (%), increase from 50 to 60 1C, and then decreased with increasing temperature. This could be due to increase in radical propagation rate, resulting to the generation of more free radicals with increase in molecular mobility [13,14]. There was also absence of grafting at 80 1C. This could also be due to rapid decomposition of APS at elevated temperature which promoted the chain transfer reaction and early termination of the growing radicals [15,16]. The results indicate that the styrene rich system was more suitable as it offered highest G(%) and Y(%) as shown in Table 1. The percentage grafting increase from 1 to 3 h, this could be attributable to increase in number of active sites on the chitosan backbone (Fig. 1). The decrease in G(%)and Y(%) above 3 h promote homopolymerization of styrene. This could be due to chains transfer and other side reactions [14]. To optimize APS content, 1:3 chitosan:styrene weight ratio was polymerized at 60 1C for 3 h using APS (0.2–1.0 g). Both G(%) and Y (%) increased with APS from 0.2 to 0.4 g, and then decreased above 0.4 g. This could be due to the formation of more initiating radicals
13
W1
1 1 1 3
W2
c
Temp (1C)
d
e
1.32 2.79 1.28 3.11
3 3 1 1
50 60 60 60
32.00 179.00 28.00 3.67
10.67 59.67 28.00 11.00
b
W3
G(%)
Y(%)
a
W1 represents weight of chitosan. W2 represents weight of washed copolymer. c W3 represents weight of washed monomer. d G(%) represents grafting percentage. e Y(%) represents percentage yield. b
Fig. 1. Effect of reaction time on the G(%) and Y(%) of samples polymerized at 60 1C and 0.4 g APS.
Scheme 1. (a) Chitosan-macroradicals, (b) chitosan-g-PS, and (d) hydrolyzed polystyrene.
14
A. Umar et al. / Materials Letters 124 (2014) 12–14
Fig. 2. FTIR SPectra of (a) chitosan and (b) chitosan-g-PS copolymer (d) hydrolyzed polystyrene.
Fig. 3. Thermogram of chitosan-g-PS copolymer.
4. Conclusion Polystyrene was successfully grafted from chitosan backbone using ammonium persulfate initiator. The optimum grafting was found to be at 1:3 chitosan:styrene weight ratio, 60 1C with 0.4 g APS and 3 h reaction time. The polystyrene grafted from chitosan has glass transition temperature of 106 1C and Mw and Mn were found to be 95,644 and 32,755, respectively, with PDI, 2.92. Acknowledgment We acknowledge the financial support for Abdulgnaiyu Umar from Malaysian International Scholarship [MIS] under the Ministry of Higher Education Malaysia [MOHE]. The authors would like to thank Universiti Teknologi Malaysia for financial support through research grant [No. Q.J130000.2626.08J42]. References [1] Harish Prashanth KV, Tharanathan RN. Chitin/chitosan: modifications and their unlimited application potential—an overview. Trends Food Sci amp; Technol 2007;18:117–31.
[2] Dumitrius S, editor. Polysaccharides in medical applications, New York: Marcel Dekker Inc.; 1996. p. 125–42. [3] Rinaudo M. Chitin and chitosan: properties and applications. Prog Polym Sci (Oxf) 2006;31:603–32. [4] Keisuke KK. Chitin and chitosan: functional biopolymers from marine crustaceans. Mar Biotechnol 2006;8:203–26. [5] Sabaa MW, Mohamed NA, Mohamed RR, Khalil NM, Abd El Latif SM. Synthesis, characterization and antimicrobial activity of poly (N-vinyl imidazole) grafted carboxymethyl chitosan. Carbohydr Polym 2010;79:998–1005. [6] Zhang J, Wang Q, Wang A. Synthesis and characterization of chitosan-g-poly (acrylic acid)/attapulgite superabsorbent composites. Carbohydr Polym 2007;68:367–74. [7] Ding W, Lian Q, Samuels RJ, Polk MB. Synthesis and characterization of a novel derivative of chitosan. Polymer 2003;44:547–56. [8] Patil MK, Nayak PL. Graft copolymerization of vinyl monomers onto chitosan: III: graft copolymerization of acrylamide onto chitosan for antibacterial activity. Int J Plant, Anim Environ Sci 2011;1:210–9. [9] Joshi JM, Sinha VK. Ceric ammonium nitrate induced grafting of polyacrylamide onto carboxymethyl chitosan. Carbohydr Polym 2007;67:427–35. [10] Srivastava A, Mishra DK, Behari K. Graft copolymerization of N-vinyl-2pyrrolidone onto chitosan: synthesis, characterization and study of physicochemical properties. Carbohydr Polym 2010;80:790–8. [11] Pillai CKS, Paul W, Sharma CP. Chitin and chitosan polymers: chemistry, solubility and fiber formation. Prog Polym Sci 2009;34:641–78. [12] Singh V, Tiwari A, Pandey S, Singh SK. Microwave-accelerated Synthesis and characterization of potato starch-g-poly(acrylamide). Starch – Stärke 2006;58: 536–43. [13] Matyjaszewski K, Xia J. Atom transfer radical polymerization. Chem Rev 2001;101:2921–90. [14] Kaewtatip K, Tanrattanakul V. Preparation of cassava starch grafted with polystyrene by suspension polymerization. Carbohydr Polym 2008;73:647–55. [15] Matyjaszewski K, Patten TE, Xia J. Controlled /“Living” radical polymerization. Kinet Homog Atom Transf Rad Polymerization Styr 1997;35:674–80. [16] Abu Naim A, Umar A, Sanagi MM, Basaruddin N. Chemical modification of chitin by grafting with polystyrene using ammonium persulfate initiator. Carbohydr Polym 2013;98:1618–23. [17] Kurita K, Hashimoto S, Yoshino H, Ishii S, Nishimura SI. Preparation of chitin/ polystyrene hybrid materials by efficient graft copolymerization based on mercaptochitin. Macromolecules 1996;29:1939–42. [18] Wang J-S, Matyjaszewski K. Controlled/“Living” radical polymerization. Halogen atom transfer radical polymerization promoted by a Cu(I)/Cu(II) redox process. Macromolecules 1995;28:7901–10.
Contents lists available at ScienceDirect
Materials Letters journal homepage: www.elsevier.com/locate/matlet
Synthesis and characterization of chitosan grafted with polystyrene using ammonium persulfate initiator Abdulganiyu Umar a, Ahmedy Abu Naim a,n, Mohd Marsin Sanagi b a b
Department of Chemistry, Faculty of Science, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia Ibnu Sina Institute for Fundamental Science Studies, Nanotechnology Research Alliance, Universiti Teknologi Malaysia, 81310 Johor Bahru, Johor, Malaysia
art ic l e i nf o
a b s t r a c t
Article history: Received 2 July 2013 Accepted 1 March 2014 Available online 11 March 2014
Graft copolymerization of styrene from chitosan was prepared under various conditions using ammonium persulfate (APS) initiator. The grafting was found to be best at 1:3 chitosan:styrene weight ratio, 0.4 g APS and temperature 60 1C. The washed products were characterized by spectroscopic and thermal methods. FT-IR analysis indicate the presence of polystyrene peaks, DSC analysis showed the improvement in Tg of the polystyrene. After acid hydrolysis, the copolymer was analyzed using gel permeation chromatography (GPC), and the result revealed the isolated polystyrene having Mw and Mn as 95,249 and 30,755 respectively, with polydispersity index, 2.92. & 2014 Elsevier B.V. All rights reserved.
Keywords: Chitosan Grafting Polystyrene Ammonium persulfate Free-radical polymerization
1. Introduction Chitosan is a deacetylated form of chitin having D-glucosamine repeating units linked by β (1-4) glycosidic bond. It is rigid and specific crystalline structure made it to exist in nature in different polymorphic forms having various properties [1]. As such its applications in both pharmaceutical and medical fields were exploited [2]. Its solubility in acidic media made it to have different applications as gels, solutions, films and fibres [3]. Chitosan is also used in food and textile industries, cosmetic, waste water treatment [4]. Chemical modification of biopolymers is an important aspect which continues to receive considerable attention. One of the applications is the formation of the graft copolymers via free radical mechanism. “Grafting onto” technique was employed to graft vinyl monomers onto chitosan using different initiators. Poly (N-vinyl imidazole) was grafted onto caboxymethyl chitosan using potassium persulfate initiator [5]. Acrylic acid was grafted onto chitosan using ammonium persulfate initiator [6]. 4-(6-methacryloxyhexyloxy)-4'-nitrobiphenyl grafted onto chitosan using AIBN as initiator [7]. Other groups used cerium ammonium nitrate as initiator [8,9]. Recently, N-vinyl-2-pyrrolidone was grafted onto chitosan using potassium bromate as initiator [10]. In the present study, we report the grafting of polystyrene from chitosan backbone using ammonium persulfate initiator. Because of the enhanced porosity gained by the addition of polystyrene,
n
Corresponding author. Tel.: þ 60 75534462; fax: þ60 75566162. E-mail address: [email protected] (A. Abu Naim).
http://dx.doi.org/10.1016/j.matlet.2014.03.007 0167-577X/& 2014 Elsevier B.V. All rights reserved.
the copolymer could be used effectively for the removal of dyes from aqueous solutions.
2. Materials and methods Chitosan (deacetylation degree 85%) and styrene were purchased from Sigma-Aldrich (St. Louis, USA), and the chitosan was used after dried in oven at 100 1C. Ammonium persulfate (APS), ethylbenzene from Acros (New Jersey, USA), methanol and chloroform from QRëc (Selangor, Malaysia). All the chemicals were used as received except styrene. Styrene was washed three times using 5% NaOH(aq) to remove the inhibitor, washed with deionized water, dried with calcium hydride (CaH2) and capped in a conical flask before use. Graft copolymerization was carried out at various reaction conditions. Chitosan solutions were prepared as described [11]. Chitosan (1 g) was dissolved in HCl(aq) (100 mL, 0.1 M) and stirred with glass rod to obtain homogenous solution. The solution was mixed with APS (0.2–1 g) in a flask, fitted with condenser, nitrogen atmosphere and stirred with magnetic bar for 40 minutes as preinteracting time. Styrene was added to the system. The reaction mixture was then heated at temperature range. The reaction was stopped by pouring the reaction mixture into methanol. The precipitate was filtered using sintered glass funnel, dried in vacuum oven at 40 1C. The crude products were washed (soxhlet extraction) for 48 h to remove any polystyrene present. The extracts were filtered and dried in vacuum oven at 50 1C. The graft product was hydrolyzed to isolate the polystyrene, by immersing the sample (1 g) in HCl (20 mL, 6 M) and stirred at 90 1C overnight. The acid
A. Umar et al. / Materials Letters 124 (2014) 12–14
was removed by simple filtration. Chloroform (30 mL) was poured onto the residue, concentrated under reduced pressure and poured into methanol to precipitate the polystyrene. Molecular weight of the isolated polystyrene was determined by gel permeation chromatography (GPC). The FT-IR spectrums of chitosan Fig. 3(a) and chitosan-g-PS Fig. 3(b) were recorded using Perkin Elmer Spectrumone spectrometer (Shelton, Connecticut, USA). The glass transition point of the graft copolymer was analyzed using Thermal Advantage Instrument Q2000 with Tzero technology having refrigerated cooling system (RCS 90), using aluminium pan under a 50 mL/min N2 flow at the heating rate of 20 1C/min on the second heating of a heating-cooling-heating cycle. A sample of approximately 11 mg was used. The samples were scanned in the temperature range 20–180 1C. The percentage grafting G(%), and yield of graft copolymerization, Y(%) were calculated according to the following equation [12]: Gð%Þ ¼
W2 W1 100 W1
ð1Þ
Yð%Þ ¼
W 2 W 1 100 W3
ð2Þ
where W1 represents weight of the chitosan, W2 represents weight of the copolymer and W3 represents weight of the styrene.
3. Results and discussion
that could promote early termination of the growing radical, which promote homopolymerization of styrene [16]. As evident from FT-IR, Fig. 2(b) indicates the presence of polystyrene peaks with IR band intensities at 3150–3000 cm 1 (C–H(aromatic)), 3000–2850 cm 1 (–C–H stretching (alkane)), 1660–1500 cm 1(C¼C aromatic) in addition to peaks due to chitosan at 3600–3200 cm 1(O–H and N–H stretching) and 1659 cm 1 due to C¼O stretching (Fig. 2a), indicating that polystyrene has successfully been grafted from chitosan. Another evidence of the graft copolymerization is, the increase in Tg to 106 1C, which was higher than the normal Tg of polystyrene (which is about 100 1C) as shown in Fig. 3, since chitosan does not possess Tg due to its rigid structure [17]. The graft copolymers were hydrolyzed with HCl(aq) as shown in Scheme 1(d). The IR spectra of the hydrolyzed product (Fig. 2(c)) resembles that of linear polystyrene, with terminal OH at 3400 cm 1. GPC analysis showed that the Mw, and Mn, of the isolated polystyrene were 95,249 and 30,755, respectively, with PDI of 2.92. The broad molecular weight distribution could be a result of non-uniform distribution of the side chains on the chitosan backbone due to slow decomposition of initiator or fast termination between growing radicals [18]. Table 1 Effect of chitosan:styrene ratio and temperature on the percentage of grafting, G(%), and yield of graft copolymerization, Y(%), of samples polymerized for 3 h with 0.1 M HCl (100 mL) and APS(0.4 g). a
Chitosan completely dissolved in 0.1 M HCl and formed a viscous solution. This could be due to high molecular weight of the polymer. Graft copolymerization was carried out in a heterogeneous phase with styrene monomer (Scheme 1). Macroradicals were generated on the chitosan backbone by adding APS. Various reaction conditions were chosen to optimize G(%) and Y(%). Grafting was carried out at different temperatures, (50–80 1C) and at 1:3, 1:1 and 3:1 chitosan:styrene weight ratio; while the APS content and reaction time were kept constant (Table 1). It was observed that the percentage grafting, G(%) and percentage yield, Y (%), increase from 50 to 60 1C, and then decreased with increasing temperature. This could be due to increase in radical propagation rate, resulting to the generation of more free radicals with increase in molecular mobility [13,14]. There was also absence of grafting at 80 1C. This could also be due to rapid decomposition of APS at elevated temperature which promoted the chain transfer reaction and early termination of the growing radicals [15,16]. The results indicate that the styrene rich system was more suitable as it offered highest G(%) and Y(%) as shown in Table 1. The percentage grafting increase from 1 to 3 h, this could be attributable to increase in number of active sites on the chitosan backbone (Fig. 1). The decrease in G(%)and Y(%) above 3 h promote homopolymerization of styrene. This could be due to chains transfer and other side reactions [14]. To optimize APS content, 1:3 chitosan:styrene weight ratio was polymerized at 60 1C for 3 h using APS (0.2–1.0 g). Both G(%) and Y (%) increased with APS from 0.2 to 0.4 g, and then decreased above 0.4 g. This could be due to the formation of more initiating radicals
13
W1
1 1 1 3
W2
c
Temp (1C)
d
e
1.32 2.79 1.28 3.11
3 3 1 1
50 60 60 60
32.00 179.00 28.00 3.67
10.67 59.67 28.00 11.00
b
W3
G(%)
Y(%)
a
W1 represents weight of chitosan. W2 represents weight of washed copolymer. c W3 represents weight of washed monomer. d G(%) represents grafting percentage. e Y(%) represents percentage yield. b
Fig. 1. Effect of reaction time on the G(%) and Y(%) of samples polymerized at 60 1C and 0.4 g APS.
Scheme 1. (a) Chitosan-macroradicals, (b) chitosan-g-PS, and (d) hydrolyzed polystyrene.
14
A. Umar et al. / Materials Letters 124 (2014) 12–14
Fig. 2. FTIR SPectra of (a) chitosan and (b) chitosan-g-PS copolymer (d) hydrolyzed polystyrene.
Fig. 3. Thermogram of chitosan-g-PS copolymer.
4. Conclusion Polystyrene was successfully grafted from chitosan backbone using ammonium persulfate initiator. The optimum grafting was found to be at 1:3 chitosan:styrene weight ratio, 60 1C with 0.4 g APS and 3 h reaction time. The polystyrene grafted from chitosan has glass transition temperature of 106 1C and Mw and Mn were found to be 95,644 and 32,755, respectively, with PDI, 2.92. Acknowledgment We acknowledge the financial support for Abdulgnaiyu Umar from Malaysian International Scholarship [MIS] under the Ministry of Higher Education Malaysia [MOHE]. The authors would like to thank Universiti Teknologi Malaysia for financial support through research grant [No. Q.J130000.2626.08J42]. References [1] Harish Prashanth KV, Tharanathan RN. Chitin/chitosan: modifications and their unlimited application potential—an overview. Trends Food Sci amp; Technol 2007;18:117–31.
[2] Dumitrius S, editor. Polysaccharides in medical applications, New York: Marcel Dekker Inc.; 1996. p. 125–42. [3] Rinaudo M. Chitin and chitosan: properties and applications. Prog Polym Sci (Oxf) 2006;31:603–32. [4] Keisuke KK. Chitin and chitosan: functional biopolymers from marine crustaceans. Mar Biotechnol 2006;8:203–26. [5] Sabaa MW, Mohamed NA, Mohamed RR, Khalil NM, Abd El Latif SM. Synthesis, characterization and antimicrobial activity of poly (N-vinyl imidazole) grafted carboxymethyl chitosan. Carbohydr Polym 2010;79:998–1005. [6] Zhang J, Wang Q, Wang A. Synthesis and characterization of chitosan-g-poly (acrylic acid)/attapulgite superabsorbent composites. Carbohydr Polym 2007;68:367–74. [7] Ding W, Lian Q, Samuels RJ, Polk MB. Synthesis and characterization of a novel derivative of chitosan. Polymer 2003;44:547–56. [8] Patil MK, Nayak PL. Graft copolymerization of vinyl monomers onto chitosan: III: graft copolymerization of acrylamide onto chitosan for antibacterial activity. Int J Plant, Anim Environ Sci 2011;1:210–9. [9] Joshi JM, Sinha VK. Ceric ammonium nitrate induced grafting of polyacrylamide onto carboxymethyl chitosan. Carbohydr Polym 2007;67:427–35. [10] Srivastava A, Mishra DK, Behari K. Graft copolymerization of N-vinyl-2pyrrolidone onto chitosan: synthesis, characterization and study of physicochemical properties. Carbohydr Polym 2010;80:790–8. [11] Pillai CKS, Paul W, Sharma CP. Chitin and chitosan polymers: chemistry, solubility and fiber formation. Prog Polym Sci 2009;34:641–78. [12] Singh V, Tiwari A, Pandey S, Singh SK. Microwave-accelerated Synthesis and characterization of potato starch-g-poly(acrylamide). Starch – Stärke 2006;58: 536–43. [13] Matyjaszewski K, Xia J. Atom transfer radical polymerization. Chem Rev 2001;101:2921–90. [14] Kaewtatip K, Tanrattanakul V. Preparation of cassava starch grafted with polystyrene by suspension polymerization. Carbohydr Polym 2008;73:647–55. [15] Matyjaszewski K, Patten TE, Xia J. Controlled /“Living” radical polymerization. Kinet Homog Atom Transf Rad Polymerization Styr 1997;35:674–80. [16] Abu Naim A, Umar A, Sanagi MM, Basaruddin N. Chemical modification of chitin by grafting with polystyrene using ammonium persulfate initiator. Carbohydr Polym 2013;98:1618–23. [17] Kurita K, Hashimoto S, Yoshino H, Ishii S, Nishimura SI. Preparation of chitin/ polystyrene hybrid materials by efficient graft copolymerization based on mercaptochitin. Macromolecules 1996;29:1939–42. [18] Wang J-S, Matyjaszewski K. Controlled/“Living” radical polymerization. Halogen atom transfer radical polymerization promoted by a Cu(I)/Cu(II) redox process. Macromolecules 1995;28:7901–10.