**Ionic Liquid as Green Solvent for Ring-Opening Graft Polymerizaion of ε-Caprolactone onto Hemicelluloses**

X.Q. Zhang, M.J. Chen, H.H. Wang, X.X. Wen, C.F. Liu and R.C. Sun

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/59679

#### **1. Introduction**

[121] Xie, H.; Zhao, Z.K. (2011). Selective breakdown of lignocellulose in ionic liquids, Chap. 4, pp. 61–80, In: Ionic Liquids: Applications and Perspectives, A. Kokorin (ed.),

[122] Orlandi, M.; Luca, Z.; Salanti, A. (2013). Characterization of lignocellulosic materials during the biorefinery process of *Arundo donax* for "fine" chemicals production, COST FP0901: Analytical Techniques for Biorefineries, Turku Seminar, Åbo Akademi

[123] Ahn, I.-S.; Yang, J.-H.;Kim, J.; Lee, S.; Mhin, B.J. (20130. Search for a new cellulose de‐ crystallization agent for the pretreatment of lignocellulosic biomasses, Int. Symp. & Annual meeting, IS4-3, p.191, *The Korean Society for Microbiology & Biotechnology*,

[124] Wasserscheid, W.; Welton, T. (2008). Ionic Liquids in Synthesis, Wiley-VCH Verlag:

[125] Abu-Eishah, S.I. (2011). Ionic liquids recycling for reuse. Chap. 11, pp. 239-272, In: Ionic Liquids – Classes and Properties. S.T. Handy (ed.), InTech, Rijeka, Croatia. [126] Peric, B.; Martí, E.; Sierra, J.; Cruañas, R.; Garau, M. A. (2012), Green chemistry: Eco‐ toxicity and biodegradability of ionic liquids, Chap. 6, pp. 89–113, In: Recent Advan‐ ces in Pharmaceutical Sciences II, D. Muñoz-Torrero, D. Haro and J. Vallès (eds.),

Weinheim, Germany, ISBN-13 978-1-4020-4087-0 (e-book).

InTech, Rijeka, Croatia.

460 Ionic Liquids - Current State of the Art

University, Finland.

www.kormb.or.kr

ISBN: 978-81-7895-569-8.

The depletion of fossil fuels has led to rapidly increasing interest in the utilization of environ‐ mentally friendly, readily available, biodegradable, and renewable biomass to produce biofuels, biocomposites, biochemicals, and a host of other bioproducts [1-3]. Agricultural crop residues, such as cereal straws and sugarcane bagasse (SCB), are underutilized lignocellulosic biomass and have great potential for the production of biocompatible and biodegradable materials to replace fossil-based products [4,5].

Hemicelluloses, the second most abundant class of renewable and biodegradable polysac‐ charides found in nature after cellulose, account for on average about 20-35% of most plant materials [6,7]. Compared with cellulose and lignin, the exploiting of hemicelluloses was paid little attention until the last decades due to their inherent low molecular weight and hetero‐ geneous structure. In their natural state, hemicelluloses are generally considered to be noncrystalline, with a DP of 80 to 200.They are heterogeneous polymers of pentose (xylose, arabinose), hexoses (mannose, glucose, and galactose), and sugar acids. Xylans are the most abundant hemicelluloses [8]. In many plant materials, xylans are heteropolysaccharides with homopolymeric backbone chains of 1,4-linked β-D-xylopyranose (Xyl*p*) units [9]. In addition, there can be *O*-acetyl, α-L-arabinofuranosyl, α-1,2-linked glucuronic, or 4-*O*-methylglucuronic acid substituents on the backbone [10].

Chemical modification is an important way to impart biomass with desired properties for specific applications [11-13]. From the chemist point of view, a broad variety of chemical modification reactions both at OH groups and the C atoms are possible [14]. Ring-opening graft polymerization (ROGP) is a multifunctional modification technique for the synthesis of

© 2015 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and eproduction in any medium, provided the original work is properly cited.

polymers from cyclic monomers that can endow polymers with controlled molecular weights and molecular weight distributions [15-17]. Due to their excellent biodegradability, biocom‐ patibility, and permeability, considerable attention has been paid to aliphatic polyesters from lactones and lactides, among which poly (ε-caprolactone) (PCL) is especially interesting for its applications [1,18,19]. It is a hydrophobic aliphatic polyester with excellent biocompatibility, low immunogenicity, nontoxicity, and good mechanical and thermoplastic properties, making it a potential matrix candidate in biocomposites [1,20,21]. Much consideration had been paid to graft copolymerization between cellulose derivatives and aliphatic polyesters [1,22,23]. In contrast to cellulose, there is a little information about the graft polymerization of biodegrad‐ able aliphatic polyesters onto hemicellulose. Moreover, reactions on hemicellulose are not easy, mainly because of the almost impossible proposition of dissolving hemicellulose in a suitable solvent without significant degradation.

In recent years, with the development of green chemistry and the requirement for environment protection, much attention has been focused on the utilization of ionic liquids as novel solvents and reaction media due to their eco-friendliness, negligible vapor pressure, non-flammability, chemical stability, good thermal stability, and high reaction rates [24]. In general, ionic liquids are screened with a range of anions, from small hydrogen-bond acceptors (Cl- ) to large noncoordinating anions, including Br- , SCN- , [PF6] - , and [BF4] - [25]. They are capable of dissolving complex polymeric materials and macromolecules, such as carbohydrates. The ionic liquids can break the extensive hydrogen-bonding network in the polysaccharides and promote their dissolution [26]. Various polysaccharide derivatives have been prepared in ionic liquids from cellulose [27,28], hemicelluloses [11,26] and starch [29]. These results indicated that there are no derivatization reactions occur during the dissolution of polysaccharides in ionic liquids. They are satisfactorily homogeneous media [30], and can be desirable alternatives to conventional solvents and reaction media in modification.

The aim of the present research was to investigate homogeneous ROGP of ε-CL onto hemi‐ celluloses using 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) ionic liquid as a homo‐ genous reaction medium with 4-dimethylaminopyridine (DMAP) as a catalyst to prepare hemicellulose-*g*-PCL copolymers. The physico-chemical properties of the graft copolymers were characterized by FT-IR, 1 H-NMR, <sup>1</sup> H-1 H Correlation Spectroscopy (COSY), 13C-NMR, 1 H-13C Correlation 2D NMR (HSQC), XRD, SEM and thermal analysis.

#### **2. Experimental**

#### **2.1. Materials**

Sugarcane bagasse (SCB) was obtained from a local sugar factory (Guangzhou, China). It was dried in sunlight and then cut into small pieces. The cut SCB was ground to pass a 0.8-mm screen. It was dried in a cabinet oven with air circulation for 20 h at 50o C.

4-Dimethylaminopyridine (DMAP, 99%) and ε-caprolactone (ε-CL, 99%) were supplied by Aladdin Reagents Co., Ltd. (Shanghai, China). The ionic liquid 1-butyl-3-methylimidazolium chloride ([C4mim]Cl, 99%) was purchased from Cheng Jie Chemical Co., Ltd. (Shanghai, China), and dried in vacuum for 48 h at 70o C before used. All other chemicals were of analytical reagent grade and directly used without further purification.

#### **2.2. Isolation and characterization of the native hemicellulose from SCB**

polymers from cyclic monomers that can endow polymers with controlled molecular weights and molecular weight distributions [15-17]. Due to their excellent biodegradability, biocom‐ patibility, and permeability, considerable attention has been paid to aliphatic polyesters from lactones and lactides, among which poly (ε-caprolactone) (PCL) is especially interesting for its applications [1,18,19]. It is a hydrophobic aliphatic polyester with excellent biocompatibility, low immunogenicity, nontoxicity, and good mechanical and thermoplastic properties, making it a potential matrix candidate in biocomposites [1,20,21]. Much consideration had been paid to graft copolymerization between cellulose derivatives and aliphatic polyesters [1,22,23]. In contrast to cellulose, there is a little information about the graft polymerization of biodegrad‐ able aliphatic polyesters onto hemicellulose. Moreover, reactions on hemicellulose are not easy, mainly because of the almost impossible proposition of dissolving hemicellulose in a

In recent years, with the development of green chemistry and the requirement for environment protection, much attention has been focused on the utilization of ionic liquids as novel solvents and reaction media due to their eco-friendliness, negligible vapor pressure, non-flammability, chemical stability, good thermal stability, and high reaction rates [24]. In general, ionic liquids

dissolving complex polymeric materials and macromolecules, such as carbohydrates. The ionic liquids can break the extensive hydrogen-bonding network in the polysaccharides and promote their dissolution [26]. Various polysaccharide derivatives have been prepared in ionic liquids from cellulose [27,28], hemicelluloses [11,26] and starch [29]. These results indicated that there are no derivatization reactions occur during the dissolution of polysaccharides in ionic liquids. They are satisfactorily homogeneous media [30], and can be desirable alternatives

The aim of the present research was to investigate homogeneous ROGP of ε-CL onto hemi‐ celluloses using 1-butyl-3-methylimidazolium chloride ([C4mim]Cl) ionic liquid as a homo‐ genous reaction medium with 4-dimethylaminopyridine (DMAP) as a catalyst to prepare hemicellulose-*g*-PCL copolymers. The physico-chemical properties of the graft copolymers

Sugarcane bagasse (SCB) was obtained from a local sugar factory (Guangzhou, China). It was dried in sunlight and then cut into small pieces. The cut SCB was ground to pass a 0.8-mm

4-Dimethylaminopyridine (DMAP, 99%) and ε-caprolactone (ε-CL, 99%) were supplied by Aladdin Reagents Co., Ltd. (Shanghai, China). The ionic liquid 1-butyl-3-methylimidazolium

H-1

, [PF6] -

, and [BF4]

H Correlation Spectroscopy (COSY), 13C-NMR,

C.

) to large


are screened with a range of anions, from small hydrogen-bond acceptors (Cl-

, SCN-

suitable solvent without significant degradation.

to conventional solvents and reaction media in modification.

H-NMR, <sup>1</sup>

H-13C Correlation 2D NMR (HSQC), XRD, SEM and thermal analysis.

screen. It was dried in a cabinet oven with air circulation for 20 h at 50o

noncoordinating anions, including Br-

462 Ionic Liquids - Current State of the Art

were characterized by FT-IR, 1

**2. Experimental**

**2.1. Materials**

1

Sugarcane bagasse was first delignified with sodium chlorite in acidic solution (pH 4.0, adjusted by 10% acetic acid) at 75 o C for 2 h. The hemicelluloses were then extracted from the holocellulose with 10% NaOH for 10 h at 20 o C with a liquor ratio of 1 to 20, followed by the acidification of the supernatant to pH 6.0 with 6M HCl and then the precipitation in 3 volumes of 95% ethanol. After filtration, the pellets of the hemicelluloses were washed with acidified 70% ethanol and then air dried. The main procedure of isolation hemicelluloses is shown in Scheme 1.

**Sheme 1** Extraction of hemicelluloses from sugarcane bagasse

#### **2.3. Synthesis of Hemicellulose-***g***-PCL copolymers in [C4mim]Cl**

Dry hemicelluloses (0.33 g, 0.005 mol of hydroxyl group in hemicelluloses) were added to [C4mim]Cl (7.5 g) in a 50-mL dried three-neck flask. The mixture was stirred at 85o C for 1 h under the protection of nitrogen to achieve a homogenous solution. Then, the required quantities of ε-CL and DMAP were added gradually over a period of 2 min into the solution. The ROGP reaction was carried out under the protection of nitrogen with vigorous stirring for 24 h. After the required time, the solution was cooled to room temperature and the resultant graft copolymer was precipitated in excessive ethanol and dialyzed with a 3000-molecular weight dialysis bag in ultrapure water for 7 days. The final product was freeze-dried for 48 h. Each sample was duplicated under the same conditions to reduce errors and confirm the results.

#### **2.4. Characterization of hemicelluloses and hemicellulose-***g***-PCL copolymers**

FT-IR spectra of unmodified hemicelluloses and hemicelluloses-*g*-PCL copolymers were recorded on an FT-IR spectrophotometer (Tensor 27, Germany) from a KBr disc containing 1% (w/w) finely ground samples in the range of 4000 to 400 cm-1. Thirty-two scans were taken for each sample, with a resolution of 2 cm-1 in the transmittance mode.

The 1 H-NMR, 1 H-1 H COSY, 13C-NMR, and 1 H-13C HSQC spectra of unmodified hemicellulose and hemicellulose-*g*-PCL copolymers were recorded from 40 mg samples in 0.5 mL DMSOd6 on a Bruker Avance III 400 M spectrometer (Germany) with a 5 mm multinuclear probe. For the 1 H-NMR analysis, the detailed collecting and processing parameters were listed as follows: number of scans, 64; receiver gain, 456; acquisition time, 1.3631 s; relaxation delay, 3.0 s; pulse width, 3.0 s; spectrometer frequency, 400.13 MHz; and spectral width, 6009.6 Hz. For the 1 H-1 H COSY analysis, the detailed collecting and processing parameters were listed as follows: number of scans, 8; receiver gain, 447; acquisition time, 0.4588 s; relaxation delay, 2.0 s; pulse width, 9.0 s; spectrometer frequency, 400.13/400.13 MHz; and spectral width, 4000.0/4000.0 Hz. For the 13C-NMR analysis, the detailed collecting and processing parameters were listed as follows: number of scans, 2112; receiver gain, 2048; acquisition time, 0.3296 s; relaxation delay, 5.0 s; pulse width, 9.8 s; spectrometer frequency, 100.61 MHz; and spectral width, 25062.7 Hz. For the 1 H-13C HSQC analysis, the detailed collecting and processing parameters were listed as follows: number of scans, 28; receiver gain, 2050; acquisition time, 0.0639 s; relaxation delay, 2.0 s; pulse width, 8.5 s; spectrometer frequency, 400.13/100.61 MHz; and spectral width, 8012.8/20161.3 Hz. The detailed structure factors of hemicellulose-*g*-PCL copolymers, includ‐ ing the degree of polymerization of PLA (DPPLA), the molar substitution of PLA (MS), the degree of substitution of PLA (DS), and the weight content of PLA side chains (WPLA), were determined by 1 H-NMR.

The thermal stability of the samples was performed using thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) on a Q500 thermogravimetric analyzer (TA, USA). Samples weighing between 9 and 11 mg were heated from room temperature to 600o Cat a thermal ramp of 10o C/min under nitrogen flow.

The surface morphology was examined by SEM on a field emission microscopy (LEO 1530 VP, LEO, Germany). The samples were prepared by casting few solids onto a mica sheet followed by gold-plating.

XRD was determined on a D/Max-III X-ray diffractometer (Rigaku, Japan) equipped with the high-intensity monochromatic nickel-filtered Cu Kα1 radiation (λ=0.154 nm). The operating voltage and current were 40 kV and 40 mA, respectively. Data were collected with diffraction angle 2θ ranging from 5 to 60° with a step size of 0.04° and time per step of 0.2 s at room temperature.

### **3. Results and discussion**

graft copolymer was precipitated in excessive ethanol and dialyzed with a 3000-molecular weight dialysis bag in ultrapure water for 7 days. The final product was freeze-dried for 48 h. Each sample was duplicated under the same conditions to reduce errors and confirm the

FT-IR spectra of unmodified hemicelluloses and hemicelluloses-*g*-PCL copolymers were recorded on an FT-IR spectrophotometer (Tensor 27, Germany) from a KBr disc containing 1% (w/w) finely ground samples in the range of 4000 to 400 cm-1. Thirty-two scans were taken for

and hemicellulose-*g*-PCL copolymers were recorded from 40 mg samples in 0.5 mL DMSOd6 on a Bruker Avance III 400 M spectrometer (Germany) with a 5 mm multinuclear probe. For

COSY analysis, the detailed collecting and processing parameters were listed as follows: number of scans, 8; receiver gain, 447; acquisition time, 0.4588 s; relaxation delay, 2.0 s; pulse width, 9.0 s; spectrometer frequency, 400.13/400.13 MHz; and spectral width, 4000.0/4000.0 Hz. For the 13C-NMR analysis, the detailed collecting and processing parameters were listed as follows: number of scans, 2112; receiver gain, 2048; acquisition time, 0.3296 s; relaxation delay, 5.0 s; pulse width, 9.8 s; spectrometer frequency, 100.61 MHz; and spectral width, 25062.7 Hz.

as follows: number of scans, 28; receiver gain, 2050; acquisition time, 0.0639 s; relaxation delay, 2.0 s; pulse width, 8.5 s; spectrometer frequency, 400.13/100.61 MHz; and spectral width, 8012.8/20161.3 Hz. The detailed structure factors of hemicellulose-*g*-PCL copolymers, includ‐ ing the degree of polymerization of PLA (DPPLA), the molar substitution of PLA (MS), the degree of substitution of PLA (DS), and the weight content of PLA side chains (WPLA), were

The thermal stability of the samples was performed using thermogravimetric analysis (TGA) and derivative thermogravimetry (DTG) on a Q500 thermogravimetric analyzer (TA, USA). Samples weighing between 9 and 11 mg were heated from room temperature to 600o

The surface morphology was examined by SEM on a field emission microscopy (LEO 1530 VP, LEO, Germany). The samples were prepared by casting few solids onto a mica sheet followed

XRD was determined on a D/Max-III X-ray diffractometer (Rigaku, Japan) equipped with the high-intensity monochromatic nickel-filtered Cu Kα1 radiation (λ=0.154 nm). The operating voltage and current were 40 kV and 40 mA, respectively. Data were collected with diffraction angle 2θ ranging from 5 to 60° with a step size of 0.04° and time per step of 0.2 s at room

C/min under nitrogen flow.

H-NMR analysis, the detailed collecting and processing parameters were listed as follows: number of scans, 64; receiver gain, 456; acquisition time, 1.3631 s; relaxation delay, 3.0 s; pulse width, 3.0 s; spectrometer frequency, 400.13 MHz; and spectral width, 6009.6 Hz. For the 1

H-13C HSQC analysis, the detailed collecting and processing parameters were listed

H-13C HSQC spectra of unmodified hemicellulose

H-1 H

Cat a

of ε‐CL.

a

b

c

d

Sample No.

The PCL content, calculated by 1

Temp ( o C)

The degree of polymerization of PCL, calculated by <sup>1</sup>

Molar composition in the graft copolymer, calculated by 1

The degree of substitution of the copolymer, calculated by <sup>1</sup>

H-NMR.

**2.4. Characterization of hemicelluloses and hemicellulose-***g***-PCL copolymers**

each sample, with a resolution of 2 cm-1 in the transmittance mode.

H COSY, 13C-NMR, and 1

results.

The 1

the 1

For the 1

determined by 1

thermal ramp of 10o

by gold-plating.

temperature.

H-NMR.

H-NMR, 1

464 Ionic Liquids - Current State of the Art

H-1

#### **3.1. Synthesis of hemicellulose-***g***-PCL copolymers in [C4mim]Cl**

DMAP and ε-CL could be easily dissolved in [C4mim]Cl within several minutes. Therefore, the homogeneous ROGP reaction of ε-CL onto hemicelluloses was performed with DMAP as a catalyst, and a schematic reaction is shown in scheme 2. The effects of reaction conditions, including reaction temperature, the molar ratios of ε-CL to anhydroxylose units (AXU) in hemicelluloses, and the dosage of DMAP catalyst on the detailed structure factors, were investigated. Table 1 shows the preparation conditions of hemicellulose-*g*-PCL copolymers and their detailed structural factors calculated from 1 H-NMR. **3. Results and discussion 3.1. Synthesis of hemicellulose‐***g***‐PCL copolymers in [C4mim]Cl** DMAP and ε‐CL could be easily dissolved in [C4mim]Cl within several minutes. Therefore, the homogeneous ROGP reaction of ε‐CL onto hemicelluloses was performed with DMAP as a catalyst, and a schematic reaction is shown in

According to the results in Table 1, an increase in reaction temperature from 110 o C to 120 o C resulted in an increase in DS from 0.03 to 0.09, DP from 1.39 to 1.45, MS from 0.04 to 0.13 and WPCL from 3.33% to 10.09%, which was probably due to the favorable effect of temperature on the molecule motion and collision with the increased temperature. However, further improve‐ ment of reaction temperature from 120 o C to 130 o C led to a decrease in DS from 0.09 to 0.06, DP from 1.45 to 1.26, MS from 0.13 to 0.07 and WPCL from10.09% to 5.71%, probably due to the increased degradation of hemicelluloses in ionic liquid at a higher temperature under the given conditions. The DS, DP, MS and WPCL of the products remarkably increased from 0.09 to 0.22, 1.45 to 1.48, 0.13 to 0.32 and 10.09% to 21.65%, respectively, with an increase in the dosage of DMAP catalyst from 2% to 3%, indicating the good catalytic ability of DMAP for ROGP of ε-CL onto hemicelluloses in [C4mim]Cl; while it significantly decreased with a further increase in DMAP dosage to 4%,indicating the detrimental effects of excessive DMAP, which was probably due to the fact that the strong basicity of DMAP inhibited the attachment of PCL onto hemicelluloses. Increasing the molar ratio of ε-CL to AXU in hemicelluloses from 1:1 to 3:1 resulted in an improvement of DS from 0.04 to 0.22, DP from 0.93 to 1.48, MS from 0.04 to 0.32 and WPCL from 3.34% to 21.65%, which was probably due to the greater availability of ε-CL in the proximity of the reactive hydrogel groups in hemicelluloses at a higher molar ratio of ε-CL to AXU. However, a further increase in the molar ratio of ε-CL to AXU from 3:1 to 5:1 led to decrease in DS, DP, MS and WPCL, which was probably due to the quick self-polymerization of ε-CL. scheme 2. The effects of reaction conditions, including reaction temperature, the molar ratios of ε‐CL to anhydroxylose units (AXU) in hemicelluloses, and the dosage of DMAP catalyst on the detailed structure factors, were investigated. Table 1 shows the preparation conditions of hemicellulose-*g*-PCL copolymers and their detailed structural factors calculated from 1 H-NMR. According to the results in Table 1, an increase in reaction temperature from 110 oC to 120 oC resulted in an increase in DS from 0.03 to 0.09, DP from 1.39 to 1.45, MS from 0.04 to 0.13 and WPCL from 3.33% to 10.09%, which was probably due to the favorable effect of temperature on the molecule motion and collision with the increased temperature. However, further improvement of reaction temperature from 120 oC to 130 oC led to a decrease in DS from 0.09 to 0.06, DP from 1.45 to 1.26, MS from 0.13 to 0.07 and WPCL from10.09% to 5.71%, probably due to the increased degradation of hemicelluloses in ionic liquid at a higher temperature under the given conditions. The DS, DP, MS and WPCL of the products remarkably increased from 0.09 to 0.22, 1.45 to 1.48, 0.13 to 0.32 and 10.09% to 21.65%, respectively, with an increase in the dosage of DMAP catalyst from 2% to 3%, indicating the good catalytic ability of DMAP for ROGP of ε-CL onto hemicelluloses in [C4mim]Cl; while it significantly decreased with a further increase in DMAP dosage to 4%,indicating the detrimental effects of excessive DMAP, which was probably due to the fact that the strong basicity of DMAP inhibited the attachment of PCL onto hemicelluloses. Increasing the molar ratio of ε‐CL to AXU in hemicelluloses from 1:1 to 3:1 resulted in an improvement of DS from 0.04 to 0.22, DP from 0.93 to 1.48, MS from 0.04 to 0.32 and WPCL from 3.34% to 21.65%, which was probably due to the greater availability of ε‐CL in the proximity of the reactive hydrogel groups in hemicelluloses at a higher molar ratio of ε‐CL to AXU. However, a further increase in the molar ratio of ε‐CL to AXU from 3:1 to 5:1 led to decrease in DS, DP, MS and WPCL, which was probably due to the quick self‐polymerization

**Scheme 2.** The ring opening graft copolymerization of ε-CL onto hemicelluloses in [C4mim]Cl with DMAP as a catalyst. **Sheme 2.** The ring opening graft copolymerization of ε-CL onto hemicelluloses in [C4mim]Cl with DMAP as a catalyst

Time

1 110 2% 3:1 24 1.39 0.04 0.03 3.33% 2 120 2% 3:1 24 1.45 0.13 0.09 10.09% 3 130 2% 3:1 24 1.26 0.07 0.06 5.71% 4 120 3% 3:1 24 1.48 0.32 0.22 21.65% 5 120 4% 3:1 24 1.39 0.03 0.02 2.52% 6 120 3% 1:1 24 0.93 0.04 0.04 3.34% 7 120 3% 2:1 24 1.26 0.07 0.06 5.70% 8 120 3% 4:1 24 1.38 0.21 0.13 13.45% 9 120 3% 5:1 24 1.29 0.11 0.08 8.68%

H-NMR.

H-NMR.

H-NMR.

(h) DPPCL<sup>a</sup> MS<sup>b</sup> DS<sup>c</sup> <sup>W</sup><sup>d</sup>

PCL

**Table 1.** Properties of hemicellulose-*g*-PCL copolymers under various conditions in [C4mim]Cl.

ε-CL/ AXU

Catalyst (wt%)


a The degree of polymerization of PCL, calculated by 1 H-NMR.

b Molar composition in the graft copolymer, calculated by 1 H-NMR.

c The degree of substitution of the copolymer, calculated by 1 H-NMR.

d The PCL content, calculated by 1 H-NMR.

**Table 1.** Properties of hemicellulose-*g*-PCL copolymers under various conditions in [C4mim]Cl.

#### **3.2. FT-IR spectra**

The FT-IR spectra of the isolated hemicelluloses and hemicellulose-*g*-PCL copolymer samples 2 and 4 are shown in Figure 1. The sharp peak at 893 cm-1 is indicative of typical β-anomers, indicating the primary β-glycosidic linkages between the sugar units in the hemicellulosic fractions [26]. The strong absorption band at 1045 cm-1 is largely due to the C-O stretching in the C-O-C linkages [26]. The small band at 1252 cm-1 originates from the C-O antisymmetric stretching in ester. The band at 1382 cm-1 corresponds to the C-H bending, and that at 1638 cm-1originates from the bending mode of the absorbed water. The peak at 1736cm-1 is the characteristic absorption of C=O stretching. The characteristic absorbance at 3431cm-1 is assigned to the hydroxyl group stretching vibrations, and that at 2910 cm-1 is attributed to the C-H stretching vibrations. In the FT-IR spectra of hemicellulose-*g*-PCL copolymers, the increased intensities of the bands at 2910, 1738, 1252, and 1170 cm-1, from C-H stretching, C=O stretching, C-O antisymmetric stretching, and C-O-C vibration, respectively, were observed compared with those in unmodified hemicelluloses, indicating the successful modification of hemicelluloses in [C4mim]Cl under the given conditions.

Ionic Liquid as Green Solvent for Ring-Opening Graft Polymerizaion of ε-Caprolactone onto Hemicelluloses http://dx.doi.org/10.5772/59679 467

**Figure 1.** FT-IR spectra of unmodified hemicelluloses (spectrum a) and hemicellulose-*g*-PCL copolymer samples 2 (spectrum b) and 4 (spectrum c) prepared in [C4mim]Cl

#### **3.3. 1 H-NMR, 1 H-1 H COSY, 13C-NMR and 1 H-13C HSQC spectra**

**Sample No.**

a

b

c

**Temp ( oC)**

466 Ionic Liquids - Current State of the Art

The degree of polymerization of PCL, calculated by 1

d The PCL content, calculated by 1

**3.2. FT-IR spectra**

Molar composition in the graft copolymer, calculated by 1

The degree of substitution of the copolymer, calculated by 1

H-NMR.

hemicelluloses in [C4mim]Cl under the given conditions.

**Table 1.** Properties of hemicellulose-*g*-PCL copolymers under various conditions in [C4mim]Cl.

**Catalyst (wt%)**

**ε-CL/ AXU**

1 110 2% 3:1 24 1.39 0.04 0.03 3.33%

2 120 2% 3:1 24 1.45 0.13 0.09 10.09%

3 130 2% 3:1 24 1.26 0.07 0.06 5.71%

4 120 3% 3:1 24 1.48 0.32 0.22 21.65%

5 120 4% 3:1 24 1.39 0.03 0.02 2.52%

6 120 3% 1:1 24 0.93 0.04 0.04 3.34%

7 120 3% 2:1 24 1.26 0.07 0.06 5.70%

8 120 3% 4:1 24 1.38 0.21 0.13 13.45%

9 120 3% 5:1 24 1.29 0.11 0.08 8.68%

H-NMR.

H-NMR.

H-NMR.

The FT-IR spectra of the isolated hemicelluloses and hemicellulose-*g*-PCL copolymer samples 2 and 4 are shown in Figure 1. The sharp peak at 893 cm-1 is indicative of typical β-anomers, indicating the primary β-glycosidic linkages between the sugar units in the hemicellulosic fractions [26]. The strong absorption band at 1045 cm-1 is largely due to the C-O stretching in the C-O-C linkages [26]. The small band at 1252 cm-1 originates from the C-O antisymmetric stretching in ester. The band at 1382 cm-1 corresponds to the C-H bending, and that at 1638 cm-1originates from the bending mode of the absorbed water. The peak at 1736cm-1 is the characteristic absorption of C=O stretching. The characteristic absorbance at 3431cm-1 is assigned to the hydroxyl group stretching vibrations, and that at 2910 cm-1 is attributed to the C-H stretching vibrations. In the FT-IR spectra of hemicellulose-*g*-PCL copolymers, the increased intensities of the bands at 2910, 1738, 1252, and 1170 cm-1, from C-H stretching, C=O stretching, C-O antisymmetric stretching, and C-O-C vibration, respectively, were observed compared with those in unmodified hemicelluloses, indicating the successful modification of

**Time (h) DPPCL <sup>a</sup> MSb DSc Wd PCL**

Figure 2 shows the 1 H-NMR spectrum of hemicellulose-*g*-PCL copolymer sample 2. The resonance peaks derived from the protons of xylan appear at 4.26, 3.03, 3.25, 3.49, 3.17 and 3.78 ppm, assigned to H-1, H-2, H-3, H-4, H-5a and H-5e, respectively[31]. The signals from the methylene proton in PCL appeared at 2.25 ppm (-COCH2-, a), 1.53 ppm (-CH2-, b, d), 1.30 ppm (-CH2-, c), 1.41 ppm (-CH2-, d'), 3.87 ppm (-CH2O-, e), 3.38 ppm (-CH2O-, e') and 4.39 ppm (- CH2OH-, e´, end unit) [17]. These observations confirmed the attachment of PCL onto hemi‐ celluloses in ionic liquid [C4mim]Cl. In addition, the signals at 4.53 and 4.87 ppm are associated with the protons at substituted C-2 and C-3 positions, respectively, confirming the attachment of PCL on C-2 and C-3 positions in AXU. Meanwhile, the detailed structural factors of hemicellulose-*g*-PCL copolymers, including DS, MS, DPPLA, and WPLA, could be calculated from the peak intensity of corresponding signals based on the following equations:

$$\text{DS} = \frac{\text{CL}\_{\text{Terminal}}}{\text{AXU}} = \frac{\text{I}\_{\text{l}}/\text{2}}{\text{I}\_{\text{H}}4} = \frac{(\text{I}\_{\text{a}} - \text{I}\_{\text{e}})}{\text{I}\_{\text{H}}4} \tag{1}$$

$$\text{MS} = \frac{\text{CL}}{\text{AXU}} = \frac{\text{I}\_{\text{a}}}{\text{2} \,\text{I}\_{\text{H}}} \tag{2}$$

$$\text{DP} = \frac{\text{CL}\_{\text{Total}}}{\text{CL}\_{\text{Terminal}}} = \frac{\text{I}\_{\text{(e+ e')}}}{\text{I}\_{\text{e'}}} = \frac{\text{I}\_{\text{a}}}{\text{I}\_{\text{a}} - \text{I}\_{\text{e}}} \tag{3}$$

$$\text{W}\_{\text{PCL}} = \frac{114 \,\text{MS}}{132 + 114 \,\text{MS}} \times 100\% \,\text{ } \tag{4}$$

where DS is the degree of substitution of PCL, DP is the degree of polymerization of PCL, MS is the molar substitution of PCL, WPCL is the weight content of PCL side chains, AXU is anhydroxylose unit, CLTerminal is the end unit of PCL, CLTotal is the total units of PCL, 2 is two protons in each methylene group, Ie, Ie' and Ia are the integral area of the resonances of the corresponding methylene protons at e, e', and a positions of PCL, and IH4 is the integral area of theresonance assigned to H4 of AXU. The 114 g mol-1 and 132 g mol-1 in equation (4) are the molecular weight of ε-caprolactone and the molecular weight of xylan unit, respectively.

The DS, MS, DPPLA, and WPLA values calculated from <sup>1</sup> H-NMR are listed in Table 1. The results indicated that the xylan derivatives with DS 0.02–0.22, DP 0.93-1.48, MS 0.03-0.32 and WPCL 2.52-21.65% were obtained under the selected conditions, lower than those of cellulose-*g*-PCL prepared in [Bmim]Cl [18]. Considering the linear macromolecular structure of cellulose with more hydroxyl groups available, which allowed for more side chains attached on the biopol‐ ymer, the estimated DS, MS, DPPLA, and WPLA values of hemicellulose-*g*-PCL copolymers in the present study were reasonable and acceptable. In addition, the different calculation equation based on the different assignments of the typical proton signals [18] was also responsible for the differences of DS, MS, DPPLA, and WPLA of the copolymers in ionic liquids.

**Figure 2.** <sup>1</sup> H-NMR spectrum of hemicellulose-*g*-PCL copolymer sample 2

To confirm the correct assignment of the primary proton signals of the attached PCL side chains, Figure 3 shows the 1 H-1 H COSY spectrum of hemicellulose-*g*-PCL copolymer sample 2. To clearly show the cross-correlations of the protons on the attached PCL side chains, the spectrum is illustrated at higher contour level and as a result the primary signals in AXU and their cross-correlations are not shown. The cross-correlations of PCL side chains, a/b, b/c, c/d', d'/e', e'/e'-OH, were clearly observed, indicating the assignment of the proton signals was correct. Moreover, the cross-correlations for repeating unit indicated the DP of xylan-*g*-PCL copolymers was over 1, which was corresponded to the results in Table 1.

**Figure 3.** <sup>1</sup> H-1 H COSY spectrum of hemicellulose-*g*-PCL copolymer sample 2

Total (e e') a Terminal e' a e

+

= == - (3)

H-NMR are listed in Table 1. The results

(4)

CL I I I

where DS is the degree of substitution of PCL, DP is the degree of polymerization of PCL, MS is the molar substitution of PCL, WPCL is the weight content of PCL side chains, AXU is anhydroxylose unit, CLTerminal is the end unit of PCL, CLTotal is the total units of PCL, 2 is two protons in each methylene group, Ie, Ie' and Ia are the integral area of the resonances of the corresponding methylene protons at e, e', and a positions of PCL, and IH4 is the integral area of theresonance assigned to H4 of AXU. The 114 g mol-1 and 132 g mol-1 in equation (4) are the molecular weight of ε-caprolactone and the molecular weight of xylan unit, respectively.

indicated that the xylan derivatives with DS 0.02–0.22, DP 0.93-1.48, MS 0.03-0.32 and WPCL 2.52-21.65% were obtained under the selected conditions, lower than those of cellulose-*g*-PCL prepared in [Bmim]Cl [18]. Considering the linear macromolecular structure of cellulose with more hydroxyl groups available, which allowed for more side chains attached on the biopol‐ ymer, the estimated DS, MS, DPPLA, and WPLA values of hemicellulose-*g*-PCL copolymers in the present study were reasonable and acceptable. In addition, the different calculation equation based on the different assignments of the typical proton signals [18] was also responsible for the differences of DS, MS, DPPLA, and WPLA of the copolymers in ionic liquids.

To confirm the correct assignment of the primary proton signals of the attached PCL side

2. To clearly show the cross-correlations of the protons on the attached PCL side chains, the

H COSY spectrum of hemicellulose-*g*-PCL copolymer sample

CL I I DP

114 MS <sup>W</sup> 100% 132 114 MS = ´ +

PCL

468 Ionic Liquids - Current State of the Art

The DS, MS, DPPLA, and WPLA values calculated from <sup>1</sup>

H-NMR spectrum of hemicellulose-*g*-PCL copolymer sample 2

H-1

**Figure 2.** <sup>1</sup>

chains, Figure 3 shows the 1

Figure 4 illustrates the 13C-NMR spectra of unmodified hemicelluloses (A) and hemicellulose*g*-PCL copolymer sample 2 (B). In Figure 4A, the five major signals at 101.8, 75.6, 74.4, 73.4, and 63.5 ppm correspond to C-1, C-4, C-2, C-3, and C-5 of the 1,4-linked β-D-Xyl*p* (xylopyra‐ nose) units, respectively [32]. The signals at 97.6, 71.6, 69.9, 82.4, 171.7, and 59.1 ppm can be assigned to C-1, C-3, C-2, C-4, C-6, and the methoxy group of the 4-*O*-methyl-D-glucuronic acid residue is linked to C-3 of the backbone of the β-D-Xyl*p* units[30]. These results indicated that the native hemicelluloses were composed of 4-*O*-methyl-D-glucuronic acid-D-xylans. In Figure 4B, the signal at 171.8 ppm is attributed to the carbonyl carbon (in position f) in the PCL segment, and those at 33.5, 24.7, 25.1, 32.1, 32.1, 63.2 and 60.4 ppm correspond to the methylene carbon signals of PCL in the a, b, d, d', e, and e' positions, respectively. The main signals of the β-D-Xyl*p* units are all observed, indicating no significant structural changes in the hemicellu‐ losic backbone. Compared with spectrum A, the relative intensity of the signal of C-3 in the β-D-Xyl*p* units slightly decreased in spectrum B, suggesting that a partial substitution occurred at the C-3 hydroxyl group.

**Figure 4.** 13C-NMR spectra of unmodified hemicelluloses (A) and hemicellulose-*g*-PCL copolymer sample 2 (B)

1 H-13C HSQC provides detailed information of signals overlapped in 1 H- and 13C-NMR spectra, and could be applied for qualitative and quantitative analysis of chemical structure. HSQC spectrum of sample 2 was illustrated in Figure 5. To exhibit the primary correlations both unsubstituted and substituted, the spectrum is illustrated at a relatively low contour level. The strong correlations at δC/δH 33.2/2.26, 24.2/1.52, 24.8/1.30, 31.9/1.38, 32.9/1.52, 60.8/3.39 and 62.7/3.88 ppm are associated with Ca-Ha, Cb-Hb, Cc-Hc, Cd'-Hd', Cd-Hd, Ce'-He' and Ce-He, respectively, indicated that the PCL side chains were successfully attached onto xylan. Clearly, the strong correlations in carbohydrate region at δC/δH 102.4/4.24, 72.9/3.02, 73.8/3.23, 75.7/3.49, 63.6/3.79, and 63.6/3.14 ppm are attributed to C1-H1, C2-H2, C3-H3, C4-H4, C5e-H5e and C5a-H5a in AXU of xylan, respectively. More importantly, the correlations at δC/δ<sup>H</sup> 72.7/4.51 and 75.1/4.81 for substituted C2-H2 (2') and substituted C3-H3 (3'), respectively, provided the possible quantitative estimation of ROGP reaction occurred at C2 and C3 positions.Clearly, more PCL side chains were attached to C3 position than to C2 position. The integrated resonances for substituted and unsubstituted C2/H2 and C3/H3 indicated that 16.34% and 83.66% of PCL side chains were attached to C2 and C3 positions of AXU, respectively.

**Figure 5.** HSQC spectrum of hemicellulose-*g*-PCL copolymer sample 2

#### **3.4. Thermal analysis**

**Figure 4.** 13C-NMR spectra of unmodified hemicelluloses (A) and hemicellulose-*g*-PCL copolymer sample 2 (B)

and could be applied for qualitative and quantitative analysis of chemical structure. HSQC spectrum of sample 2 was illustrated in Figure 5. To exhibit the primary correlations both unsubstituted and substituted, the spectrum is illustrated at a relatively low contour level. The strong correlations at δC/δH 33.2/2.26, 24.2/1.52, 24.8/1.30, 31.9/1.38, 32.9/1.52, 60.8/3.39 and 62.7/3.88 ppm are associated with Ca-Ha, Cb-Hb, Cc-Hc, Cd'-Hd', Cd-Hd, Ce'-He' and Ce-He, respectively, indicated that the PCL side chains were successfully attached onto xylan. Clearly, the strong correlations in carbohydrate region at δC/δH 102.4/4.24, 72.9/3.02, 73.8/3.23, 75.7/3.49, 63.6/3.79, and 63.6/3.14 ppm are attributed to C1-H1, C2-H2, C3-H3, C4-H4, C5e-H5e and C5a-H5a in AXU of xylan, respectively. More importantly, the correlations at δC/δ<sup>H</sup> 72.7/4.51 and 75.1/4.81 for substituted C2-H2 (2') and substituted C3-H3 (3'), respectively, provided the possible quantitative estimation of ROGP reaction occurred at C2 and C3 positions.Clearly, more PCL side chains were attached to C3 position than to C2 position. The integrated resonances for

H- and 13C-NMR spectra,

H-13C HSQC provides detailed information of signals overlapped in 1

1

470 Ionic Liquids - Current State of the Art

The thermal properties of unmodified hemicelluloses and hemicellulose-*g*-PCL copolymers were studied using TGA (Figure 6A) in the temperature range from 50o C to 600o C under a nitrogen atmosphere. Clearly, the thermal decomposition can be divided into three distinct stages. In the first stage, the weight loss observed below 100o C was the result of evaporation of moisture. At the second stage, the unmodified hemicelluloses began to decompose at about 215o C, while hemicellulose-*g*-PCL copolymer samples 2 and 4 started to decompose at about 200o C. The decomposition temperature for a 50% weight loss occurred at 280o C for unmodified hemicelluloses, 275o C for hemicellulose-*g*-PCL copolymer sample 2, and 270o C for sample 4. In the third stage, the weight marginally decreased after 300o C for ummodified hemicelluloses, after 320o C for sample 2, and after 350o C for sample 4. These results indicated that the thermal stability of hemicellulose-*g*-PCL copolymers decreased after grafting in ionic liquid compared with that of unmodified hemicelluloses. In addition, complete thermal decomposition of hemicellulose-*g*-PCL copolymers required either a higher temperature or a longer time.

To further explore the thermal degradation process, derivatives of TGA for the unmodified hemicelluloses and the hemicellulose-*g*-PCL copolymers were studied, as shown in Figure 6B. 1

2

**Ionic liquid as green solvent for ROGP of ε-caprolactone onto hemicelluloses**

11

3 **Fig.6.** TGA (A) and DTG (B) curves of unmodified hemicelluloses and hemicellulose-*g*-PCL 4 copolymer samples 2 and 4. **Figure 6.** TGA (A) and DTG (B) curves of unmodified hemicelluloses and hemicellulose-*g*-PCL copolymer samples 2 and 4

5 To further explore the thermal degradation process, derivatives of TGA for the

DTGmax represents the maximum degradation rate and can be used to compare the thermal stability between the samples [33]. Unmodified hemicelluloses showed the maximum degra‐ dation rate at about 278o C, while hemicellulose-*g*-PCL copolymer sample 2 showed two degradation peaks, at 231o C and 293o C.In general, it is impossible to avoid the degradation of biopolymers during dissolution and derivatization in ionic liquids [24,34]. The former DTGmax was due to the decomposition of hemicelluloses, providing the evidence of degrada‐ tion of the hemicellulose substance in ionic liquids. Sample 4 exhibited a similar thermal stability to that of hemicelluloses, with a DTGmax at 231 o C, indicating the similar degradation of hemicelluloses in [C4mim]Cl under the given conditions. These results indicated that the thermal stability of hemicellulose-*g*-PCL copolymers decreased after grafting in ionic liquid compared with that of unmodified hemicelluloses. The latter DTGmax was due to the decom‐ position of PCL side chains. Compared with sample 2, the second DTGmax of sample 4 with 6 unmodified hemicelluloses and the hemicellulose-*g*-PCL copolymers were studied, as 7 shown in Figure6B. DTGmax represents the maximum degradation rate and can be used to 8 compare the thermal stability between the samples [33]. Unmodified hemicelluloses showed the maximum degradation rate at about 278<sup>o</sup> 9 C, while hemicellulose-*g*-PCL copolymer sample 2 showed two degradation peaks, at 231<sup>o</sup> C and 293<sup>o</sup> 10 C.In general, it is impossible to 11 avoid the degradation of biopolymers during dissolution and derivatization in ionic liquids 12 [24,34]. The former DTGmax was due to the decomposition of hemicelluloses, providing the 13 evidence of degradation of the hemicellulose substance in ionic liquids. Sample 4 exhibited a similar thermal stability to that of hemicelluloses, with a DTGmax at 231 <sup>o</sup> 14 C, indicating the 15 similar degradation of hemicelluloses in [C4mim]Cl under the given conditions. These results 16 indicated that the thermal stability of hemicellulose-*g*-PCL copolymers decreased after 17 grafting in ionic liquid compared with that of unmodified hemicelluloses. The latter DTGmax

increased attachment of PCL increased to 304o C, indicating improved thermal stability with the enhanced PCL attachment. The higher thermal stability of the attached PCL compared to that of hemicelluloses was confirmed. A similar improved thermal stability of glucuronoxylan from aspen wood was also reported after acetylation [35].

#### **3.5. SEM**

DTGmax represents the maximum degradation rate and can be used to compare the thermal stability between the samples [33]. Unmodified hemicelluloses showed the maximum degra‐

**Figure 6.** TGA (A) and DTG (B) curves of unmodified hemicelluloses and hemicellulose-*g*-PCL copolymer samples 2

3 **Fig.6.** TGA (A) and DTG (B) curves of unmodified hemicelluloses and hemicellulose-*g*-PCL

To further explore the thermal degradation process, derivatives of TGA for the unmodified hemicelluloses and the hemicellulose-*g*-PCL copolymers were studied, as shown in Figure6B. DTGmax represents the maximum degradation rate and can be used to compare the thermal stability between the samples [33]. Unmodified hemicelluloses showed the maximum degradation rate at about 278<sup>o</sup> 9 C, while hemicellulose-*g*-PCL copolymer

C and 293<sup>o</sup> 10 C.In general, it is impossible to avoid the degradation of biopolymers during dissolution and derivatization in ionic liquids [24,34]. The former DTGmax was due to the decomposition of hemicelluloses, providing the evidence of degradation of the hemicellulose substance in ionic liquids. Sample 4 exhibited a similar thermal stability to that of hemicelluloses, with a DTGmax at 231 <sup>o</sup> 14 C, indicating the similar degradation of hemicelluloses in [C4mim]Cl under the given conditions. These results indicated that the thermal stability of hemicellulose-*g*-PCL copolymers decreased after grafting in ionic liquid compared with that of unmodified hemicelluloses. The latter DTGmax

**Ionic liquid as green solvent for ROGP of ε-caprolactone onto hemicelluloses**

biopolymers during dissolution and derivatization in ionic liquids [24,34]. The former DTGmax was due to the decomposition of hemicelluloses, providing the evidence of degrada‐ tion of the hemicellulose substance in ionic liquids. Sample 4 exhibited a similar thermal

of hemicelluloses in [C4mim]Cl under the given conditions. These results indicated that the thermal stability of hemicellulose-*g*-PCL copolymers decreased after grafting in ionic liquid compared with that of unmodified hemicelluloses. The latter DTGmax was due to the decom‐ position of PCL side chains. Compared with sample 2, the second DTGmax of sample 4 with

C and 293o

stability to that of hemicelluloses, with a DTGmax at 231 o

sample 2 showed two degradation peaks, at 231<sup>o</sup>

C, while hemicellulose-*g*-PCL copolymer sample 2 showed two

C.In general, it is impossible to avoid the degradation of

C, indicating the similar degradation

11

dation rate at about 278o

4 copolymer samples 2 and 4.

472 Ionic Liquids - Current State of the Art

1

2

and 4

degradation peaks, at 231o

To investigate how chemical modification affects the morphology of hemicelluloses, a series of SEM observation of native hemicelluloses and hemicelluloses-*g*-PCL copolymers are illustrated in Figure 7. The changes of the morphology of the native and modified hemicellu‐ loses were clearly observed with different reaction conditions. The unmodified hemicelluloses showed fluffy block structure, with a smooth and dense surface, and porous structure was clearly observed for the native and modified hemicelluloses. Compared with native hemicel‐ luloses, the all hemicelluloses-*g*-PCL copolymers displayed more smaller and ruleless lamellar structure when grafting PCL onto it.

**Figure 7.** Scanning electron micrographs of the surface of unmodified hemicelluloses (a) and hemicelluloses-*g*-PCL co‐ polymer samples 2 (b), 4 (c) and 8 (d)

**Figure 8.** X-ray diffraction patterns of unmodified hemicelluloses (a) and hemicelluloses-*g*-PCL copolymersamples2 (b), 4 (c), 8 (d) and 9 (e)

#### **3.6. XRD**

The crystal structure of hemicelluloses and hemicelluloses-*g*-PCL copolymers were studied using X-ray diffraction analysis and the X-ray diffraction patterns are shown in Figure 8. In spectrum a of native hemicelluloses, there are two small significant diffraction peaks at 2θ 11.2o and 12.4 o, and a strong peak at 19.1o . The strong diffraction peak are shifted in the spectra of hemicelluloses-g-PCL samples 2, 4, 8, and 9 to 20.2o (b), 20.9o (c), 20.4o (d) and 19.8o (e), respectively, and the intensity of diffraction patterns decreased. The small peaks at 11.2 o and 12.4 o could not be observed in the diffraction patterns of hemicelluloses-*g*-PCL copolymers. These changes suggested that the original crystalline structure of hemicelluloses was disrupted by modification under homogeneous conditions in ionic liquid.

#### **4. Conclusions**

Homogeneous ring opening graft polymerization (ROGP) of ε-caprolactone (ε-CL) onto hemicelluloses was achieved using 4-dimethylaminopyridine (DMAP) as a catalyst in 1 butyl-3-methylimidazolium chloride ([C4mim]Cl) ionic liquid. The detailed structural factors determined from 1 H-NMR indicated that the optimized synthesis of hemicellulose-*g*-PCL copolymers with a PCL content of 21.65% was performed at 120o C for 24 h with the molar ratio of ε-CL to AXU 3:1 and 3% DMAP. The results from FT-IR, 1 H-NMR, 13C-NMR, COSY and HSQC analyses confirmed the attachment of PCL to hemicelluloses. TGA/DTG suggested the decreased thermal stability of hemicelluloses after ROGP in [C4mim]Cl and confirmed the higher thermal stability of the attached PCL than that of hemicelluloses. Considering the good biodegradability of hemicellulose and PCL, this kind of hemicellulose-g-PCL copolymers could be used as environmentally friendly materials.

#### **Acknowledgements**

This work was financially supported by the National Natural Science Foundation of China (31170550), Program for New Century Excellent Talents in University (NCET-11-0154), the Fundamental Research Funds for the Central Universities, and the National Program for Support of Top-notch Young Professionals.

### **Author details**

X.Q. Zhang1 , M.J. Chen1 , H.H. Wang1 , X.X. Wen1 , C.F. Liu1\* and R.C. Sun1,2

\*Address all correspondence to: chfliu@scut.edu.cn

1 State Key Laboratory of Pulp and Paper Engineering, South China University of Technology, Guangzhou, P. R. China

2 Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing, P. R. China

#### **References**

**3.6. XRD**

(b), 4 (c), 8 (d) and 9 (e)

474 Ionic Liquids - Current State of the Art

11.2o

**4. Conclusions**

determined from 1

and 12.4 o, and a strong peak at 19.1o

of hemicelluloses-g-PCL samples 2, 4, 8, and 9 to 20.2o (b), 20.9o

by modification under homogeneous conditions in ionic liquid.

copolymers with a PCL content of 21.65% was performed at 120o

of ε-CL to AXU 3:1 and 3% DMAP. The results from FT-IR, 1

The crystal structure of hemicelluloses and hemicelluloses-*g*-PCL copolymers were studied using X-ray diffraction analysis and the X-ray diffraction patterns are shown in Figure 8. In spectrum a of native hemicelluloses, there are two small significant diffraction peaks at 2θ

**Figure 8.** X-ray diffraction patterns of unmodified hemicelluloses (a) and hemicelluloses-*g*-PCL copolymersamples2

respectively, and the intensity of diffraction patterns decreased. The small peaks at 11.2 o and 12.4 o could not be observed in the diffraction patterns of hemicelluloses-*g*-PCL copolymers. These changes suggested that the original crystalline structure of hemicelluloses was disrupted

Homogeneous ring opening graft polymerization (ROGP) of ε-caprolactone (ε-CL) onto hemicelluloses was achieved using 4-dimethylaminopyridine (DMAP) as a catalyst in 1 butyl-3-methylimidazolium chloride ([C4mim]Cl) ionic liquid. The detailed structural factors

H-NMR indicated that the optimized synthesis of hemicellulose-*g*-PCL

. The strong diffraction peak are shifted in the spectra

(c), 20.4o (d) and 19.8o

C for 24 h with the molar ratio

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