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A fibrous hypercrosslinked sorbent prepared on PP-ST-DVB matrix via post-crosslinking reaction
Chinese Chemical Letters 18 (2007) 588–590 www.elsevier.com/locate/cclet
A fibrous hypercrosslinked sorbent prepared on PP-ST-DVB matrix via post-crosslinking reaction Feng Liu a, Si Guo Yuan a,*, Xiao Li Wang a, A.P. Polikarpov b, A.A. Shunkevich b a
b
School of Chemical Engineering, Zhengzhou University, Zhengzhou 450002, China Institute of Physical Organic Chemistry, National Academy of Sciences, Minsk 220072, Belarus Received 25 December 2006
Abstract A fibrous sorbent possessing abundant micropore structure was firstly prepared via post-crosslinking reaction on the PP-ST-DVB original fiber. Its micromorphology and sorptive properties were investigated, and the results demonstrated that the novel fibrous hypercrosslinked sorbent has narrow pore-size distribution, small average porous radius (1.90 nm), high specific surface area (362.31 m2/g), and fine sorptive properties for small organic molecules. # 2007 Si Guo Yuan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Fibrous hypercrosslinked sorbent; Prepare; Micropore structure
The crosslinked and porous structure of functional polymers impose a great influence upon their reaction kinetics, selective adsorption and osmotic stability [1]. Many novel granular functional polymers possessing abundant porous structure have been developed. Due to the deep research of above fields, their application field also has spread quickly. However, owing to linear chain structure of fiber-forming polymer, it is impossible to build crosslinked network and abundant pore structure on the preparation of fiber-forming polymer by traditional suspension polymerization method. Up to now, no systematic investigations on the crosslinked and porous characteristics of organic functional fibers have been reported. On continuing our efforts in the design and preparation of porous skeleton structure of functional fiber, herein, a novel sorptive fiber possessing abundance micropore network was firstly prepared. The typical process is shown as follows. The polypropylene-(g)-styrene-divinyl benzene (PP-ST-DVB) fiber and 4,40 -dichloromethyl biphenyl (molar ratio = 2:1), as the original fiber and rigid crosslinking agent, were immersed in a mixture solvent system overnight. SnCl4, as the catalyst, was added to above reaction solution at 0–5 8C, and kept the temperature for 30 min. Then the post-crosslinking reaction was carried out at 80 8C for 10 h. To increase the post-crosslink degree and specific surface area (SSA) of hypercrosslinked fiber, above reaction can be repeated at the same conditions for 1–3 times. After filtration, the fiber product was extracted with acetone in a Soxhlet apparatus, washed with aq. HCl and de-ionized water sequentially, and then dried in a vacuum oven at 60 8C.
* Corresponding author. E-mail address: [email protected] (S.G. Yuan). 1001-8417/$ – see front matter # 2007 Si Guo Yuan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2007.03.036
F. Liu et al. / Chinese Chemical Letters 18 (2007) 588–590
589
Fig. 1. Scheme of PP-ST-DVB original fiber.
Swelling behavior is very important to the reaction on the polymer matrix. In thermodynamically ‘good’ solvents, the side-chains of polymer have enough extension and mobility, and the crosslinking bridges can easily form. Unlike ST-DVB resin, ST and DVB segments, as side groups or branched chains, were attached to PP main chain of original fiber in our experiment (Fig. 1). Owing to the structural difference of fiber and resin materials, their reactivity and swelling capacities also show obvious difference. By the determination of swelling capacity of various solvents, a mixture solvent system (volume ratio: dichloroethane:nitrobenzene:cyclohexane = 1:1:1) was adopted in present investigation. Usually the activity of the catalyst is FeCl3 > SnCl4 > ZnCl2 in the solution phase of Friedel–Crafts alkylation. But SnCl4 shows a higher catalytic activity in our investigation. Maybe it can be ascribed to high solubility in above solvent system. To further increase the specific surface area (SSA) of hypercrosslinked fiber, a multi-crosslinking process was adopted sometimes. The experimental results show that the SSA and weight of final fiber are decreased sharply when the post-crosslinking reaction reaches a certain level. It could be attributed to the desquamation of network fragments, as well as the collapse of polymer matrix, at high post-crosslinking degree. The crosslinking degree (DVB content) of original fiber is an important factor for the post-crosslinking reaction. The higher the crosslinking degree is, the high SSA possession of the final products more difficult is. Table 1 gives the results of post-crosslinking reaction of original fiber with same grafting degree of ST (197%) and various DVB contents. A similar conclusion can be found in literatures [2]. The porous characteristics of original and hypercrosslinked fibers were measured by BET method on NOVA 1000e Surface Area & Pore Size Analyzer. It is easy to see that the SSA and pore volume sharply increased, and the rigid micropore network was also formed gradually during the post-crosslinking reaction. For example, the SSA and pore volume of the final fiber are 362.31 m2/g and 0.345 ml/g, respectively. But those of the original fiber are only 0.1 m2/g and 0.0006 ml/g (Table 2). Noticeably, the average pore size of hypercrosslinked fiber is obviously less than that of the macroporous resin. The 33% and 76% of pore volume of the hypercrosslinked fiber belong to the range of micropores (R 1 nm) and small-size mesopores(R 5 nm), respectively. It is correspondence to the pore characteristics of hypercrosslinked resins [3] (Fig. 2).
Table 1 Influence of the crosslinking degree of original fiber The crosslinking degree (%) 2
SSA of the first reaction (m /g) SSA of the final fiber (m2/g)
2.0
1.0
0.5
0.3
16.17 –
28.67 217.69
38.12 –
46.19 362.31
Table 2 Micromorphology of the original and post-crosslinking fibers Fibers
SSA (m2/g)
Pore volume (ml/g)
Average pore radius (nm)
Original fiber Hypercrosslinked fiber
0.1 362.31
0.0006 0.345
11.50 1.90
590
F. Liu et al. / Chinese Chemical Letters 18 (2007) 588–590
Fig. 2. Pore size distribution of the original and hypercrosslinked fiber.
Fig. 3. SEM of the hypercroslinked adsorption fiber and the original PP-ST-DVB fiber. (1) The fibrous hypercroslinked sorbent; (2) the original PP-ST-DVB fiber.
Fig. 3 shows the micromorphology of hypercroslinked fiber and the original fiber, respectively. Besides some cracks and cavities formed during post-crosslinking reaction, the novel hypercrosslinking fiber shows a continuous gel phase structure. It is different to the morphology of macroporous resin. The latter shows a ‘discrete phase structure’ or labyrinth of channels [1]. The sorptive property of hypercrosslinked fiber was investigated primarily. Its sorptive capacities for toluene and phenol were 5.20 and 0.85 mmol/g at situation toluene vapor and phenol solution (6.99 mmol/l), respectively. It can be expected that the novel fibrous materials have a good application potential for the sorption of non-polar (or weak polar) molecules. Acknowledgment The authors are grateful for the support of the National Natural Science Foundation of China (No. 20574063). References [1] D.C. Sherrington, J. Polym. Sci. Polym. Chem. 39 (2001) 2364. [2] M.P. Tsyurupa, V.A. Davankov, Reactive Funct. Polym. 53 (2002) 193. [3] M.P. Tsyurupa, V.A. Davankov, Reactive Funct. Polym. 66 (2006) 768.
A fibrous hypercrosslinked sorbent prepared on PP-ST-DVB matrix via post-crosslinking reaction Feng Liu a, Si Guo Yuan a,*, Xiao Li Wang a, A.P. Polikarpov b, A.A. Shunkevich b a
b
School of Chemical Engineering, Zhengzhou University, Zhengzhou 450002, China Institute of Physical Organic Chemistry, National Academy of Sciences, Minsk 220072, Belarus Received 25 December 2006
Abstract A fibrous sorbent possessing abundant micropore structure was firstly prepared via post-crosslinking reaction on the PP-ST-DVB original fiber. Its micromorphology and sorptive properties were investigated, and the results demonstrated that the novel fibrous hypercrosslinked sorbent has narrow pore-size distribution, small average porous radius (1.90 nm), high specific surface area (362.31 m2/g), and fine sorptive properties for small organic molecules. # 2007 Si Guo Yuan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. Keywords: Fibrous hypercrosslinked sorbent; Prepare; Micropore structure
The crosslinked and porous structure of functional polymers impose a great influence upon their reaction kinetics, selective adsorption and osmotic stability [1]. Many novel granular functional polymers possessing abundant porous structure have been developed. Due to the deep research of above fields, their application field also has spread quickly. However, owing to linear chain structure of fiber-forming polymer, it is impossible to build crosslinked network and abundant pore structure on the preparation of fiber-forming polymer by traditional suspension polymerization method. Up to now, no systematic investigations on the crosslinked and porous characteristics of organic functional fibers have been reported. On continuing our efforts in the design and preparation of porous skeleton structure of functional fiber, herein, a novel sorptive fiber possessing abundance micropore network was firstly prepared. The typical process is shown as follows. The polypropylene-(g)-styrene-divinyl benzene (PP-ST-DVB) fiber and 4,40 -dichloromethyl biphenyl (molar ratio = 2:1), as the original fiber and rigid crosslinking agent, were immersed in a mixture solvent system overnight. SnCl4, as the catalyst, was added to above reaction solution at 0–5 8C, and kept the temperature for 30 min. Then the post-crosslinking reaction was carried out at 80 8C for 10 h. To increase the post-crosslink degree and specific surface area (SSA) of hypercrosslinked fiber, above reaction can be repeated at the same conditions for 1–3 times. After filtration, the fiber product was extracted with acetone in a Soxhlet apparatus, washed with aq. HCl and de-ionized water sequentially, and then dried in a vacuum oven at 60 8C.
* Corresponding author. E-mail address: [email protected] (S.G. Yuan). 1001-8417/$ – see front matter # 2007 Si Guo Yuan. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved. doi:10.1016/j.cclet.2007.03.036
F. Liu et al. / Chinese Chemical Letters 18 (2007) 588–590
589
Fig. 1. Scheme of PP-ST-DVB original fiber.
Swelling behavior is very important to the reaction on the polymer matrix. In thermodynamically ‘good’ solvents, the side-chains of polymer have enough extension and mobility, and the crosslinking bridges can easily form. Unlike ST-DVB resin, ST and DVB segments, as side groups or branched chains, were attached to PP main chain of original fiber in our experiment (Fig. 1). Owing to the structural difference of fiber and resin materials, their reactivity and swelling capacities also show obvious difference. By the determination of swelling capacity of various solvents, a mixture solvent system (volume ratio: dichloroethane:nitrobenzene:cyclohexane = 1:1:1) was adopted in present investigation. Usually the activity of the catalyst is FeCl3 > SnCl4 > ZnCl2 in the solution phase of Friedel–Crafts alkylation. But SnCl4 shows a higher catalytic activity in our investigation. Maybe it can be ascribed to high solubility in above solvent system. To further increase the specific surface area (SSA) of hypercrosslinked fiber, a multi-crosslinking process was adopted sometimes. The experimental results show that the SSA and weight of final fiber are decreased sharply when the post-crosslinking reaction reaches a certain level. It could be attributed to the desquamation of network fragments, as well as the collapse of polymer matrix, at high post-crosslinking degree. The crosslinking degree (DVB content) of original fiber is an important factor for the post-crosslinking reaction. The higher the crosslinking degree is, the high SSA possession of the final products more difficult is. Table 1 gives the results of post-crosslinking reaction of original fiber with same grafting degree of ST (197%) and various DVB contents. A similar conclusion can be found in literatures [2]. The porous characteristics of original and hypercrosslinked fibers were measured by BET method on NOVA 1000e Surface Area & Pore Size Analyzer. It is easy to see that the SSA and pore volume sharply increased, and the rigid micropore network was also formed gradually during the post-crosslinking reaction. For example, the SSA and pore volume of the final fiber are 362.31 m2/g and 0.345 ml/g, respectively. But those of the original fiber are only 0.1 m2/g and 0.0006 ml/g (Table 2). Noticeably, the average pore size of hypercrosslinked fiber is obviously less than that of the macroporous resin. The 33% and 76% of pore volume of the hypercrosslinked fiber belong to the range of micropores (R 1 nm) and small-size mesopores(R 5 nm), respectively. It is correspondence to the pore characteristics of hypercrosslinked resins [3] (Fig. 2).
Table 1 Influence of the crosslinking degree of original fiber The crosslinking degree (%) 2
SSA of the first reaction (m /g) SSA of the final fiber (m2/g)
2.0
1.0
0.5
0.3
16.17 –
28.67 217.69
38.12 –
46.19 362.31
Table 2 Micromorphology of the original and post-crosslinking fibers Fibers
SSA (m2/g)
Pore volume (ml/g)
Average pore radius (nm)
Original fiber Hypercrosslinked fiber
0.1 362.31
0.0006 0.345
11.50 1.90
590
F. Liu et al. / Chinese Chemical Letters 18 (2007) 588–590
Fig. 2. Pore size distribution of the original and hypercrosslinked fiber.
Fig. 3. SEM of the hypercroslinked adsorption fiber and the original PP-ST-DVB fiber. (1) The fibrous hypercroslinked sorbent; (2) the original PP-ST-DVB fiber.
Fig. 3 shows the micromorphology of hypercroslinked fiber and the original fiber, respectively. Besides some cracks and cavities formed during post-crosslinking reaction, the novel hypercrosslinking fiber shows a continuous gel phase structure. It is different to the morphology of macroporous resin. The latter shows a ‘discrete phase structure’ or labyrinth of channels [1]. The sorptive property of hypercrosslinked fiber was investigated primarily. Its sorptive capacities for toluene and phenol were 5.20 and 0.85 mmol/g at situation toluene vapor and phenol solution (6.99 mmol/l), respectively. It can be expected that the novel fibrous materials have a good application potential for the sorption of non-polar (or weak polar) molecules. Acknowledgment The authors are grateful for the support of the National Natural Science Foundation of China (No. 20574063). References [1] D.C. Sherrington, J. Polym. Sci. Polym. Chem. 39 (2001) 2364. [2] M.P. Tsyurupa, V.A. Davankov, Reactive Funct. Polym. 53 (2002) 193. [3] M.P. Tsyurupa, V.A. Davankov, Reactive Funct. Polym. 66 (2006) 768.