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Synthesis and characterization of polymer-immobilized β-cyclodextrin with an inclusion recognition functionality
Reactive polymers ELSEVIER
Reactive Polymers 24 (1994) 9-16
Synthesis and characterization of polymer-immobilized / -cyclodextrin with an inclusion recognition functionality X i a o - B i n Z h a o , Bing-Lin H e * Institute of Polymer Chemistry, Nankai University, Tianjin, 300071, People's Republic of China Received 17 January 1994; accepted in revised form 22 April 1994
Abstract
A series of /~-cyclodextrin (fl-CyD) was immobilized onto the crosslinked styrene/divinylbenzene copolymer which embedded polyglycidylmethacrylate. The resulting fl-CyD polymeric adsorbent possesses a specific inclusion recognition with the aromatic compounds. The structures and properties of the grafted copolymer were characterized in detail. Their application for the adsorption of phenol and its derivatives was also assessed.
Keywords:/~-Cyclodextrin; fl-Cyclodextrin polymer; Inclusion recognition; Adsorption of phenol
1. Introduction
Cyclodextrins (CyDs), cyclic oligomers of 68 glucose molecules, form inclusion complexes with various guest compounds. For this reason, CyDs have been used to stimulate an enzyme reaction and applied widely in many fields, such as chromatographic separation and purification, the pharmaceutical industry, the food industry and agriculture, etc. [1-3]. It is well established that polymers containing CyDs can also have the ability to form inclusion complexes with molecules with a suitable size and shape. The polymer consisting of cyclodextrin (CyDP) can be prepared by the reaction of CyDs with polyfunctional compounds, or the immobilization of CyDs onto the polymeric supports [4,5]. Much study has been carried out on the immobilization of CyDs onto the inorganic supports * Corresponding author.
[6-8], and most of the immobilizations require the postmodification of CyDs. This type of work is laborious and the amount of CyDs on the polymers is relatively low because of the steric effect of the large size of the CyD molecules. Synthetically crosslinked polymeric supports have been used for the immobilization of/~-CyD which consists of 7 units of glucose. They have the inclusion recognition ability for many compounds. We have recently reported some immobilization methods by which the fl-CyD was directly linked to the macroporous or gel-type adsorbents [9,10]. These methods are simple and practical for the preparation of polymers consisting of fl-CyD. The fl-CyD polymeric adsorbents formed in this way might be applied as specific biomedical adsorbents for the removal by hemoperfusion of various toxins accumulated in the human body. The immobilization of large-size molecules such as CyDs onto the polymeric supports is difficult. One of the effective ways is to use the macroporous polymeric
0923-1137/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved. SSDI 0923-1137(94)00049-B
X.B. Zhao, B.L. He~Reactive Polymers 24 (1994) 9-16
10
CH3
CH 3 \0 /
~"
~
A[BN
~'/~ . I + -'(CH2- iC)-m --- r"':///////'~~ ~ CCH-2- )-;n C =O ~ I /O\ I COOH2-CH-CH2 OCH2- CH -/CH 2
(PS)
PS-PGMA)
OH ~ PS-PGMA L
CIH3
O
CIH3 + -(CH2-C)-
- -
PGMA
OH 0
OH
(/3- CyDP) Scheme 1. The immobilization of #-CyD onto S-DVB supports.
supports [9]. Connected with a spacer, the polymeric supports are advantageous for the immobilization of B-CyD. The immobilization route is shown in Scheme 1.
2. Experimental 2.1. Materials fl-CyD used was recrystallized and dried at 110°C under vacuum before use. The monomers such as styrene and glycidyl methacrylate were distilled under vacuum before use. Phenol, 2,4dinitrophenol, 2-nitrophenol and 4-nitrophenol were analytical reagents.
2.2. Measurements 2. 2.1. Synthesis of the crosslinked polystyrene beads The copolymer beads of styrene and divinylbenzene varying from 2 to 50% were synthesized by suspension polymerization, and the formed copolymer beads were either gel-type resin or macroporous copolymer prepared in the presence of a porogenic agent. 2.2.2. Grafting of the polyglycidylmethacrylate (PGMA) onto the crosslinked polystyrene An adequate amount of gel-type or macroporous polystyrene beads was placed into a 3-
necked bottle, the acetone solution of AIBN/ GMA (1:10, weight ratio) was then added to soak the beads overnight. After the removal of the acetone under vacuum at room temperature, the polystyrene (PS) beads containing AIBN and GMA were suspended in water containing 20% NaC1 and 3% carboxmethylcellulose (CMC). The mixture was then stirred at 70°C for 8 h under N2 atmosphere. The filtered product was washed with hot distilled water and acetone and then extracted with ethanol for 4 h and dried at room temperature. The content of the epoxy group was determined by the titration method as described in Ref. [11].
2.2.3. Immobilization of fl-CyD onto the PS-PGMA An adequate amount of PS-PGMA was added to a 3-necked bottle to swell in a dry dimethylformamide (DMF) solution for several hours, then a NaCI solution with a slight excess of fl-CyD was added [9]. The mixture was stirred at 70°C for 8 h. The filtered product was washed with hot distilled water, methanol and acetone, then dried. The amount of fl-CyD immobilized was measured by the method shown above. IR spectra were taken using a Nicolet 5DXIR spectrophotometer. UV-Visible spectra were taken by a UV-Visible recording spectrophotometer (UV-240, Shimadzu). Raman spectra
X.B. Zhao, B.L. He~Reactive Polymers 24 (1994) 9-16
11
decrease in the amount of immobilized/3-CyD. This is due to the steric effect of the polymeric supports. In addition, the macroporous supports with adequate degrees of crosslinking of 6 and 10% can obtain a high percentage of immobilization of/~-CyD.
were measured by a Spex 1403 Raman spectrophotometer. The epoxy content of the PSP G M A was measured according to the method described in Ref. [11]. The amount of fl-CyD immobilized onto the polymer supports was measured according to the method described in Ref. [9]. The water sorption capacity and the test of the inclusion-adsorption capacity for phenols were carried out as described in Refs. [12] and [9], respectively.
3.2. Effect of the content of epoxy group
The gel-type copolymer of styrene with 2% divinylbenzene and the macroporous copolymer of styrene with 10% divinylbenzene were first swollen overnight with a solution of GMA/AIBN/acetone in which the amount of GMA added was gradually increased. With this method, the epoxy content of the crosslinked PS-PGMA formed in this way increased gradually. Fig. 1 shows that the increase in the epoxy group will lead to an increase in the amount of fl-CyD immobilized. In addition, the crosslinked macroporous PS-PGMA has a higher amount of immobilization of/3-CyD than that of the gel-type resin when the epoxy content is below 1.5 mmol/g. With the increase in the content of PGMA grafted onto the crosslinked polystyrene, the outer surface of the crosslinked PS-PGMA beads will be blocked by a layer of PGMA, which inhibits the diffusion of/3-CyD in-
3. Results and discussion
The gel-type or macroporous copolymer of SDVB consisting of residual double bonds which can be applied for grafting of the above-mentioned polymer. Thus, the crosslinked polystyrene grafting with P G M A can give a high content of epoxy groups for the immobilization of/3-CyD. The experimental results are shown in Table 1. From the results in Table 1, it can be seen that the immobilization procedure is influenced by many factors. For examples, see below. 3.1. Effect on crosslinked texture
Table 1 shows that the increase in the degree of crosslinking of the polymers will lead to a
Table 1 Synthesis of fl-CyDP and their physicochemical properties No. 1a Degree of crosslinking (%) Specific surface area (m2/g) A B Average pore size (/~) A B Epoxy content (mmol/g) Amount of/~-CyD immobilized (#mol/g) Water content (%) A B
3
2
4
5
6a
7
2.0
6.0
10.0
16.0
23.0
35.0
40.0
0.80 0
48.3 0
65.5 1.2
84.5 8.28
85.4 12.5
0 0
204.4 15.4
0 0 3.23 251.6
182.3 20.5 3.14 315.4
124.5 15.8 3.74 313.2
0 0 2.95 108.0
55.8 26.6 2.82 88.6
0 0 3.16 40.7
60.4 30.5 2.47 43.5
12.0 60.5
10.0 58.5
8.5 53.5
6.0 30.5
6.0 21.3
6.5 20.5
7.4 37.5
A, before immobilization; B, after immobilization. a Gel-type resin.
X.B. Zhao, B.L. He/Reactive Polymers 24 (1994) 9-16
12
cn
"-~ 350.0
~'~ 350.0 0
v
E
"5
zL- 3 0 0 . 0
E~.3 0 0 , 0 13
.~ 2 5 0 . 0
a•
.13 0
.m
E E
150.0 0 100.0
:D 0
E <[
~o-
250.0
o 200.0
E 200.0
"~
.--A'--
0
o
•
"- 150,0 r-,, L) ' 100.0
5o.o
50.0 "1 0
o.o 0
0.5
1.0
1.5 2.0 2.5 3.0 3.5 4.0 Epoxy Content (mmol/g)
Fig. 1. Influence of epoxy content of PS-PGMA on the amount of fl-CyD immobilized. O, 2%; e, 10%. Reaction conditions: temperature, 70"C; time, 8 h; molar feeding ratio of/%CyD/epoxy group, 1 : 1.
E <
o.o
I
o
2
4
6
8 10 12 Time (hours)
14
16
Fig. 3. Influence of time on the amount of fl-CyD immobilized. Reaction conditions: temperature 70°C; molar feeding ratio of fl-CyD/epoxy group, 1 : 1; zx, 10%; O, 2%; u, 45%.
3.3. Effect of the time immobilization to the inner pores of the crosslinked PS-PGMA supports and thus decreases the amount of flCyD immobilized. This can be seen in the SEM diagrams of Fig. 2. On the other hand, the lower degree of crosslinking of the gel-type polymer is favorable for the immobilization of fl-CyD because it has larger pore diameters (at wet state).
In Fig. 3, it can be seen that the highest amount of fl-CyD immobilized can be obtained after the reaction has been carried out for 8 h.
3.4. Effect of temperature on immobilization With the increasing of temperature for the immobilization of/%CyD, the amount of/%CyD
Fig. 2. SEM analysis of crosslinked polystyrene (left), PS-PGMA (middle) and fl-CyDP2 (right).
X.B. Zhao, B.L. He~Reactive Polymers 24 (1994) 9-16
13
% -6 E
350.0
u. 3 0 0 . 0 "o
N 250.0 ~3 O
E 200.0 E 150.0 0 ~-
100.0
*d
50.0
V'
II
o
E <~
o.o o
10
20
3
4 50 60 70 Temperature (°C)
80
Fig. 4. Influence of temperature on the amount of fl-CyD immobilized. Reaction conditions: time, 8 h; molar feeding ratio of/%CyD/epoxy group, 1 : 1; O, 10%; O, 2%.
immobilized increases and then cuts down when the temperature goes above 70°C (see Fig. 4). This is because at a temperature higher than 70°C there might be combination or decomposition taking place during the reaction of fl-CyD and the polymer.
3.5. Characterization of the structures and properties of fl-CyDP 3.5.1. Characterization of fl-CyDP After P G M A is grafted onto the crosslinked polystyrene, there is a strong absorption at 1731 cm -1, which represents the vibrational stretching of the C = C bond. When/%CyD is immobilized onto the PS-PGMA support, the absorption at 3420 cm -1 indicates the vibrational stretching of the O H bond. From the IR spectra of fl-CyDP, the strong adsorption at 1032 cm -1 represents the stretching of C - O ether bonds. All these indicate the formation of/~-CyDP (see Fig. 5). 3.5.2. Characterization of the structure of fl-CyDP by Raman spectra By measuring the Raman spectra of crosslinked polystyrene and its derivatives, such as PS-PGMA and ]3-CyDP, the existence of resid-
L 4600.0 3800,0 3000,0 i
___
i
i
2200.0
1800.0
I 1400.0
1 1000,0
WGvenumbers
I 600.0
i
50t0.0
400.0
( c m -1 )
Fig. 5. IR structures of PS, PS-PGMA and/~-CyDP.
ual double bonds, is indicated, from the Raman spectra shown in Figs. 6 and 7, it can be seen that the C = C bond has a specific strong dispersion band at 1604 cm -1, and the aromatic benzene ring at 1002 c m - < The ratio of the intensity of dispersion at 1604 and 1002 cm -1 (11604/I1002) is related to the ratio of the molar content of the C = C group and the benzene ring unit. After grafting PGMA, the value of the 116o4/11oo2 of the PS-PGMA decreases. This indicates the participation of double bonds in grafting with GMA. When the fl-CyD is introduced into the supports, the value decreases considerably. With the increase in the amount of/%CyD immobilized, the value of I1604/11002 decreases gradually (see Tables 2 and 3). The mechanism by which immobilized/~-CyD affects the values of 11604/11002is not very clear at present. It is purported that the inclusion inter-
Table 2 The comparison of the 116o4/11oo2 values of PS, PS-PGMA and/%CyDP
11604/11002 PS PS-PGMA fl-CyDP
Degree of crosslinking (%) 2.0
10.0
50.0
0.280 0.167 0.085
0.288 0.208 0.093
0.378 0.222 0.143
X.B. Zhao, B.L. He~Reactive Polymers 24 (1994) 9-16
14
1002
1604
I
500.00
I
I
I
I
I
I
I
I
1200.00
1900.00 Raman Shift (cm -~) Fig. 6. Raman spectra of PS (1), PS-PGMA (2) and 3-CyDP3 (3).
1002 1604
500.00
1200.00 Raman
Shift
1900.00 ( c m -1)
Fig. 7. Raman spectra of fl-CyDP3 with different amounts of/~-CyD immobilized (see Table 3).
action between fl-CyD and the double bonds is involved.
3.5.2. Characterization of the hydrophilicityof fl-CyDP Table 1 shows that the hydrophilicity of flCyDP is related to the amount of /%CyD im-
mobilized and the degree of crosslinking of the polymeric supports. After the immobilization of the hydrophilic/%CyD, the water content of/% CyDP is larger than that of the PS-PGMA and the higher the crosslinking, the less the water content. Table 4 shows the adsorption capacity for phenol by /%CyDP. The adsorption is due to the
X..B. Zhao, B.L. He~Reactive Polymers 24 (1994) 9-16 Table 3 The comparison of the 11604/11002 values of /LCyDP with different amounts of fl-CyD immobilized a
Table 5 The inclusion recognition ability of/]-CyDP for substituted phenols Sample
No.
1 Amount of/%CyD immobilized (#mol/g) 116o4/Iloo2
0 0.208
2 50.0 0.185
3
Phenol
313.4 0.093
PS-PGMA-2 a fl-CyDP-2 a
a The degree of crosslinking of PS is 10%.
2-Nitro-
2,4-Dinitro-
phenol
phenol
phenol
8.6 35.4
9.5 12.6
5.2 0
such as 2- and 4-nitro-substituted aromatic compounds. The experimental results are shown in Table 5. From Table 5, it can be deduced that/%CyDP has different capacities for the adsorption of the substituted aromatic compounds. The order of adsorption is as follows: 4-nitrophenol > 2-nitrophenol >2,4-dinitrophenol. It is surprising that the 2,4-dinitrophenol is not adsorbed by/3-CyDP2. This might be due to the fact that the size of the 2,4-dinitrophenol is too large to diffuse into the cavity of the/3-CyD.
i
c~ 250~-
o/
o
"~c~ 1 5,0
•
1.4 24.2
4-Nitro
a Number 2 adsorbents in Table 4.
3o.ok
2o.oL
Adsorption capacity (mg/g)
4
110.5 0.143
15
Q
O 0 ~r' l J f I I I I I 0.0 80.0 160.O 24~0.0 320.0 Amount of f3-CD immobilized ( p m o l / g ) Fig. 8. Influence of the amount of/]-CyD immobilized on the phenol sorption capacity.
4. Conclusions By grafting the functional polymer as PGMA onto the polymeric support, followed by the immobilization of fl-CyD, a series of fl-CyD polymers are thus obtained. The fl-CyD formed in this way has the inclusion ability for aromatic compounds, such as phenol and its derivatives. It might be used as a specific adsorbent for the separation of isomers, and the adsorption
inclusion interaction between /3-CyD and phenol. The amount of adsorption increases with increasing amounts of fl-CyD immobilized in the polymeric adsorbent (see Fig. 8). In addition, the immobilized fl-CyD polymers possesses apparent inclusion ability for isomeric compounds Table 4 The adsorption capacity for phenol No.
1 Degree of crosslinking (%) Adsorption capacity (mg/g) A B
Amount of immobilized/3-CyD (/zmol/g) Amount of theoretical adsorption (mg/g) a
2
3
4
5
6
7
8
9
2.0
6.0
10.0
16.0
23.0
30.0
35.0
40.0
50.0
0.8 20.3 251.6 23.6
1.4 24.2 315.4 29.6
1.6 23.5 313.2 29.4
8.5 20.0 108.0 10.2
2.3 11.7 88.6 8.33
10.0 16.7 98.7 9.28
11.5 16.7 40.7 3.83
12.3 18.3 43.5 3.78
12.0 15.7 65.8 6.19
A, the adsorption capacity by PS-PGMA; B, the adsorption by/%CyDE a The theoretical amount of adsorption for phenol is calculated on the 1 : 1 molar ratio of fl-CyD to phenol.
16
X.B. Zhao, B.L. He~Reactive Polymers 24 (1994) 9-16
of aromatic toxins for environmental protection and biomedical purposes. Acknowledgement The authors are grateful for the financial support of the National Natural Science Foundation of China. References [1] M.L. Bender and M. Komiyama, Cyclodextrin Chemistry, Springer, Berlin, 1978. [2] J. Szejtli, Cyclodextrins and their Inclusion Complexes, Akademial Keidel, Budapest, 1982.
[3] J. Szejtli, Cyclodextrin Technology, Akademial Keidel, Budapest, 1988. [4] J.L. Hoffman, J. Macromol. Sci. Chem., A-7 (1973) 1147. [5] D.W. Armstrong and W. Demond, Z Chromatogr Sci., 22 (1984) 411. [6] Y. Kawaguchi, M. Tanaka, M. Nakae, K. Funazo and T. Shono, Ana/. Chem., 55 (1983) 1852. [7] C.E. Lin, C.H. Chert, C.H. Lin, M.H. Yang and J.C. Jiang, J. Chromatogr Sci., 27 (1989) 665. [8] M. Tanaka, H. Ikeda and T. Shono, at. Chromatogr., 398 (1987) 165. [9] B.L He and X.B. Zhao, Sci. China (B), 22 (1992) 1240. [10] B.L. He and X.B. Zhao, Chem. J. Chin. Univ., 13 (1992) 1472. [11] C.P. Wu, C.H. Zhou and EX. Li, Experiments of Polymer Chemistry, Anhui Science and Technology, Hefei, China, 1989, p. 272. [12] B.L. He and X.B. Zhao, React. Polymers, 18 (1992) 229.
Reactive Polymers 24 (1994) 9-16
Synthesis and characterization of polymer-immobilized / -cyclodextrin with an inclusion recognition functionality X i a o - B i n Z h a o , Bing-Lin H e * Institute of Polymer Chemistry, Nankai University, Tianjin, 300071, People's Republic of China Received 17 January 1994; accepted in revised form 22 April 1994
Abstract
A series of /~-cyclodextrin (fl-CyD) was immobilized onto the crosslinked styrene/divinylbenzene copolymer which embedded polyglycidylmethacrylate. The resulting fl-CyD polymeric adsorbent possesses a specific inclusion recognition with the aromatic compounds. The structures and properties of the grafted copolymer were characterized in detail. Their application for the adsorption of phenol and its derivatives was also assessed.
Keywords:/~-Cyclodextrin; fl-Cyclodextrin polymer; Inclusion recognition; Adsorption of phenol
1. Introduction
Cyclodextrins (CyDs), cyclic oligomers of 68 glucose molecules, form inclusion complexes with various guest compounds. For this reason, CyDs have been used to stimulate an enzyme reaction and applied widely in many fields, such as chromatographic separation and purification, the pharmaceutical industry, the food industry and agriculture, etc. [1-3]. It is well established that polymers containing CyDs can also have the ability to form inclusion complexes with molecules with a suitable size and shape. The polymer consisting of cyclodextrin (CyDP) can be prepared by the reaction of CyDs with polyfunctional compounds, or the immobilization of CyDs onto the polymeric supports [4,5]. Much study has been carried out on the immobilization of CyDs onto the inorganic supports * Corresponding author.
[6-8], and most of the immobilizations require the postmodification of CyDs. This type of work is laborious and the amount of CyDs on the polymers is relatively low because of the steric effect of the large size of the CyD molecules. Synthetically crosslinked polymeric supports have been used for the immobilization of/~-CyD which consists of 7 units of glucose. They have the inclusion recognition ability for many compounds. We have recently reported some immobilization methods by which the fl-CyD was directly linked to the macroporous or gel-type adsorbents [9,10]. These methods are simple and practical for the preparation of polymers consisting of fl-CyD. The fl-CyD polymeric adsorbents formed in this way might be applied as specific biomedical adsorbents for the removal by hemoperfusion of various toxins accumulated in the human body. The immobilization of large-size molecules such as CyDs onto the polymeric supports is difficult. One of the effective ways is to use the macroporous polymeric
0923-1137/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved. SSDI 0923-1137(94)00049-B
X.B. Zhao, B.L. He~Reactive Polymers 24 (1994) 9-16
10
CH3
CH 3 \0 /
~"
~
A[BN
~'/~ . I + -'(CH2- iC)-m --- r"':///////'~~ ~ CCH-2- )-;n C =O ~ I /O\ I COOH2-CH-CH2 OCH2- CH -/CH 2
(PS)
PS-PGMA)
OH ~ PS-PGMA L
CIH3
O
CIH3 + -(CH2-C)-
- -
PGMA
OH 0
OH
(/3- CyDP) Scheme 1. The immobilization of #-CyD onto S-DVB supports.
supports [9]. Connected with a spacer, the polymeric supports are advantageous for the immobilization of B-CyD. The immobilization route is shown in Scheme 1.
2. Experimental 2.1. Materials fl-CyD used was recrystallized and dried at 110°C under vacuum before use. The monomers such as styrene and glycidyl methacrylate were distilled under vacuum before use. Phenol, 2,4dinitrophenol, 2-nitrophenol and 4-nitrophenol were analytical reagents.
2.2. Measurements 2. 2.1. Synthesis of the crosslinked polystyrene beads The copolymer beads of styrene and divinylbenzene varying from 2 to 50% were synthesized by suspension polymerization, and the formed copolymer beads were either gel-type resin or macroporous copolymer prepared in the presence of a porogenic agent. 2.2.2. Grafting of the polyglycidylmethacrylate (PGMA) onto the crosslinked polystyrene An adequate amount of gel-type or macroporous polystyrene beads was placed into a 3-
necked bottle, the acetone solution of AIBN/ GMA (1:10, weight ratio) was then added to soak the beads overnight. After the removal of the acetone under vacuum at room temperature, the polystyrene (PS) beads containing AIBN and GMA were suspended in water containing 20% NaC1 and 3% carboxmethylcellulose (CMC). The mixture was then stirred at 70°C for 8 h under N2 atmosphere. The filtered product was washed with hot distilled water and acetone and then extracted with ethanol for 4 h and dried at room temperature. The content of the epoxy group was determined by the titration method as described in Ref. [11].
2.2.3. Immobilization of fl-CyD onto the PS-PGMA An adequate amount of PS-PGMA was added to a 3-necked bottle to swell in a dry dimethylformamide (DMF) solution for several hours, then a NaCI solution with a slight excess of fl-CyD was added [9]. The mixture was stirred at 70°C for 8 h. The filtered product was washed with hot distilled water, methanol and acetone, then dried. The amount of fl-CyD immobilized was measured by the method shown above. IR spectra were taken using a Nicolet 5DXIR spectrophotometer. UV-Visible spectra were taken by a UV-Visible recording spectrophotometer (UV-240, Shimadzu). Raman spectra
X.B. Zhao, B.L. He~Reactive Polymers 24 (1994) 9-16
11
decrease in the amount of immobilized/3-CyD. This is due to the steric effect of the polymeric supports. In addition, the macroporous supports with adequate degrees of crosslinking of 6 and 10% can obtain a high percentage of immobilization of/~-CyD.
were measured by a Spex 1403 Raman spectrophotometer. The epoxy content of the PSP G M A was measured according to the method described in Ref. [11]. The amount of fl-CyD immobilized onto the polymer supports was measured according to the method described in Ref. [9]. The water sorption capacity and the test of the inclusion-adsorption capacity for phenols were carried out as described in Refs. [12] and [9], respectively.
3.2. Effect of the content of epoxy group
The gel-type copolymer of styrene with 2% divinylbenzene and the macroporous copolymer of styrene with 10% divinylbenzene were first swollen overnight with a solution of GMA/AIBN/acetone in which the amount of GMA added was gradually increased. With this method, the epoxy content of the crosslinked PS-PGMA formed in this way increased gradually. Fig. 1 shows that the increase in the epoxy group will lead to an increase in the amount of fl-CyD immobilized. In addition, the crosslinked macroporous PS-PGMA has a higher amount of immobilization of/3-CyD than that of the gel-type resin when the epoxy content is below 1.5 mmol/g. With the increase in the content of PGMA grafted onto the crosslinked polystyrene, the outer surface of the crosslinked PS-PGMA beads will be blocked by a layer of PGMA, which inhibits the diffusion of/3-CyD in-
3. Results and discussion
The gel-type or macroporous copolymer of SDVB consisting of residual double bonds which can be applied for grafting of the above-mentioned polymer. Thus, the crosslinked polystyrene grafting with P G M A can give a high content of epoxy groups for the immobilization of/3-CyD. The experimental results are shown in Table 1. From the results in Table 1, it can be seen that the immobilization procedure is influenced by many factors. For examples, see below. 3.1. Effect on crosslinked texture
Table 1 shows that the increase in the degree of crosslinking of the polymers will lead to a
Table 1 Synthesis of fl-CyDP and their physicochemical properties No. 1a Degree of crosslinking (%) Specific surface area (m2/g) A B Average pore size (/~) A B Epoxy content (mmol/g) Amount of/~-CyD immobilized (#mol/g) Water content (%) A B
3
2
4
5
6a
7
2.0
6.0
10.0
16.0
23.0
35.0
40.0
0.80 0
48.3 0
65.5 1.2
84.5 8.28
85.4 12.5
0 0
204.4 15.4
0 0 3.23 251.6
182.3 20.5 3.14 315.4
124.5 15.8 3.74 313.2
0 0 2.95 108.0
55.8 26.6 2.82 88.6
0 0 3.16 40.7
60.4 30.5 2.47 43.5
12.0 60.5
10.0 58.5
8.5 53.5
6.0 30.5
6.0 21.3
6.5 20.5
7.4 37.5
A, before immobilization; B, after immobilization. a Gel-type resin.
X.B. Zhao, B.L. He/Reactive Polymers 24 (1994) 9-16
12
cn
"-~ 350.0
~'~ 350.0 0
v
E
"5
zL- 3 0 0 . 0
E~.3 0 0 , 0 13
.~ 2 5 0 . 0
a•
.13 0
.m
E E
150.0 0 100.0
:D 0
E <[
~o-
250.0
o 200.0
E 200.0
"~
.--A'--
0
o
•
"- 150,0 r-,, L) ' 100.0
5o.o
50.0 "1 0
o.o 0
0.5
1.0
1.5 2.0 2.5 3.0 3.5 4.0 Epoxy Content (mmol/g)
Fig. 1. Influence of epoxy content of PS-PGMA on the amount of fl-CyD immobilized. O, 2%; e, 10%. Reaction conditions: temperature, 70"C; time, 8 h; molar feeding ratio of/%CyD/epoxy group, 1 : 1.
E <
o.o
I
o
2
4
6
8 10 12 Time (hours)
14
16
Fig. 3. Influence of time on the amount of fl-CyD immobilized. Reaction conditions: temperature 70°C; molar feeding ratio of fl-CyD/epoxy group, 1 : 1; zx, 10%; O, 2%; u, 45%.
3.3. Effect of the time immobilization to the inner pores of the crosslinked PS-PGMA supports and thus decreases the amount of flCyD immobilized. This can be seen in the SEM diagrams of Fig. 2. On the other hand, the lower degree of crosslinking of the gel-type polymer is favorable for the immobilization of fl-CyD because it has larger pore diameters (at wet state).
In Fig. 3, it can be seen that the highest amount of fl-CyD immobilized can be obtained after the reaction has been carried out for 8 h.
3.4. Effect of temperature on immobilization With the increasing of temperature for the immobilization of/%CyD, the amount of/%CyD
Fig. 2. SEM analysis of crosslinked polystyrene (left), PS-PGMA (middle) and fl-CyDP2 (right).
X.B. Zhao, B.L. He~Reactive Polymers 24 (1994) 9-16
13
% -6 E
350.0
u. 3 0 0 . 0 "o
N 250.0 ~3 O
E 200.0 E 150.0 0 ~-
100.0
*d
50.0
V'
II
o
E <~
o.o o
10
20
3
4 50 60 70 Temperature (°C)
80
Fig. 4. Influence of temperature on the amount of fl-CyD immobilized. Reaction conditions: time, 8 h; molar feeding ratio of/%CyD/epoxy group, 1 : 1; O, 10%; O, 2%.
immobilized increases and then cuts down when the temperature goes above 70°C (see Fig. 4). This is because at a temperature higher than 70°C there might be combination or decomposition taking place during the reaction of fl-CyD and the polymer.
3.5. Characterization of the structures and properties of fl-CyDP 3.5.1. Characterization of fl-CyDP After P G M A is grafted onto the crosslinked polystyrene, there is a strong absorption at 1731 cm -1, which represents the vibrational stretching of the C = C bond. When/%CyD is immobilized onto the PS-PGMA support, the absorption at 3420 cm -1 indicates the vibrational stretching of the O H bond. From the IR spectra of fl-CyDP, the strong adsorption at 1032 cm -1 represents the stretching of C - O ether bonds. All these indicate the formation of/~-CyDP (see Fig. 5). 3.5.2. Characterization of the structure of fl-CyDP by Raman spectra By measuring the Raman spectra of crosslinked polystyrene and its derivatives, such as PS-PGMA and ]3-CyDP, the existence of resid-
L 4600.0 3800,0 3000,0 i
___
i
i
2200.0
1800.0
I 1400.0
1 1000,0
WGvenumbers
I 600.0
i
50t0.0
400.0
( c m -1 )
Fig. 5. IR structures of PS, PS-PGMA and/~-CyDP.
ual double bonds, is indicated, from the Raman spectra shown in Figs. 6 and 7, it can be seen that the C = C bond has a specific strong dispersion band at 1604 cm -1, and the aromatic benzene ring at 1002 c m - < The ratio of the intensity of dispersion at 1604 and 1002 cm -1 (11604/I1002) is related to the ratio of the molar content of the C = C group and the benzene ring unit. After grafting PGMA, the value of the 116o4/11oo2 of the PS-PGMA decreases. This indicates the participation of double bonds in grafting with GMA. When the fl-CyD is introduced into the supports, the value decreases considerably. With the increase in the amount of/%CyD immobilized, the value of I1604/11002 decreases gradually (see Tables 2 and 3). The mechanism by which immobilized/~-CyD affects the values of 11604/11002is not very clear at present. It is purported that the inclusion inter-
Table 2 The comparison of the 116o4/11oo2 values of PS, PS-PGMA and/%CyDP
11604/11002 PS PS-PGMA fl-CyDP
Degree of crosslinking (%) 2.0
10.0
50.0
0.280 0.167 0.085
0.288 0.208 0.093
0.378 0.222 0.143
X.B. Zhao, B.L. He~Reactive Polymers 24 (1994) 9-16
14
1002
1604
I
500.00
I
I
I
I
I
I
I
I
1200.00
1900.00 Raman Shift (cm -~) Fig. 6. Raman spectra of PS (1), PS-PGMA (2) and 3-CyDP3 (3).
1002 1604
500.00
1200.00 Raman
Shift
1900.00 ( c m -1)
Fig. 7. Raman spectra of fl-CyDP3 with different amounts of/~-CyD immobilized (see Table 3).
action between fl-CyD and the double bonds is involved.
3.5.2. Characterization of the hydrophilicityof fl-CyDP Table 1 shows that the hydrophilicity of flCyDP is related to the amount of /%CyD im-
mobilized and the degree of crosslinking of the polymeric supports. After the immobilization of the hydrophilic/%CyD, the water content of/% CyDP is larger than that of the PS-PGMA and the higher the crosslinking, the less the water content. Table 4 shows the adsorption capacity for phenol by /%CyDP. The adsorption is due to the
X..B. Zhao, B.L. He~Reactive Polymers 24 (1994) 9-16 Table 3 The comparison of the 11604/11002 values of /LCyDP with different amounts of fl-CyD immobilized a
Table 5 The inclusion recognition ability of/]-CyDP for substituted phenols Sample
No.
1 Amount of/%CyD immobilized (#mol/g) 116o4/Iloo2
0 0.208
2 50.0 0.185
3
Phenol
313.4 0.093
PS-PGMA-2 a fl-CyDP-2 a
a The degree of crosslinking of PS is 10%.
2-Nitro-
2,4-Dinitro-
phenol
phenol
phenol
8.6 35.4
9.5 12.6
5.2 0
such as 2- and 4-nitro-substituted aromatic compounds. The experimental results are shown in Table 5. From Table 5, it can be deduced that/%CyDP has different capacities for the adsorption of the substituted aromatic compounds. The order of adsorption is as follows: 4-nitrophenol > 2-nitrophenol >2,4-dinitrophenol. It is surprising that the 2,4-dinitrophenol is not adsorbed by/3-CyDP2. This might be due to the fact that the size of the 2,4-dinitrophenol is too large to diffuse into the cavity of the/3-CyD.
i
c~ 250~-
o/
o
"~c~ 1 5,0
•
1.4 24.2
4-Nitro
a Number 2 adsorbents in Table 4.
3o.ok
2o.oL
Adsorption capacity (mg/g)
4
110.5 0.143
15
Q
O 0 ~r' l J f I I I I I 0.0 80.0 160.O 24~0.0 320.0 Amount of f3-CD immobilized ( p m o l / g ) Fig. 8. Influence of the amount of/]-CyD immobilized on the phenol sorption capacity.
4. Conclusions By grafting the functional polymer as PGMA onto the polymeric support, followed by the immobilization of fl-CyD, a series of fl-CyD polymers are thus obtained. The fl-CyD formed in this way has the inclusion ability for aromatic compounds, such as phenol and its derivatives. It might be used as a specific adsorbent for the separation of isomers, and the adsorption
inclusion interaction between /3-CyD and phenol. The amount of adsorption increases with increasing amounts of fl-CyD immobilized in the polymeric adsorbent (see Fig. 8). In addition, the immobilized fl-CyD polymers possesses apparent inclusion ability for isomeric compounds Table 4 The adsorption capacity for phenol No.
1 Degree of crosslinking (%) Adsorption capacity (mg/g) A B
Amount of immobilized/3-CyD (/zmol/g) Amount of theoretical adsorption (mg/g) a
2
3
4
5
6
7
8
9
2.0
6.0
10.0
16.0
23.0
30.0
35.0
40.0
50.0
0.8 20.3 251.6 23.6
1.4 24.2 315.4 29.6
1.6 23.5 313.2 29.4
8.5 20.0 108.0 10.2
2.3 11.7 88.6 8.33
10.0 16.7 98.7 9.28
11.5 16.7 40.7 3.83
12.3 18.3 43.5 3.78
12.0 15.7 65.8 6.19
A, the adsorption capacity by PS-PGMA; B, the adsorption by/%CyDE a The theoretical amount of adsorption for phenol is calculated on the 1 : 1 molar ratio of fl-CyD to phenol.
16
X.B. Zhao, B.L. He~Reactive Polymers 24 (1994) 9-16
of aromatic toxins for environmental protection and biomedical purposes. Acknowledgement The authors are grateful for the financial support of the National Natural Science Foundation of China. References [1] M.L. Bender and M. Komiyama, Cyclodextrin Chemistry, Springer, Berlin, 1978. [2] J. Szejtli, Cyclodextrins and their Inclusion Complexes, Akademial Keidel, Budapest, 1982.
[3] J. Szejtli, Cyclodextrin Technology, Akademial Keidel, Budapest, 1988. [4] J.L. Hoffman, J. Macromol. Sci. Chem., A-7 (1973) 1147. [5] D.W. Armstrong and W. Demond, Z Chromatogr Sci., 22 (1984) 411. [6] Y. Kawaguchi, M. Tanaka, M. Nakae, K. Funazo and T. Shono, Ana/. Chem., 55 (1983) 1852. [7] C.E. Lin, C.H. Chert, C.H. Lin, M.H. Yang and J.C. Jiang, J. Chromatogr Sci., 27 (1989) 665. [8] M. Tanaka, H. Ikeda and T. Shono, at. Chromatogr., 398 (1987) 165. [9] B.L He and X.B. Zhao, Sci. China (B), 22 (1992) 1240. [10] B.L. He and X.B. Zhao, Chem. J. Chin. Univ., 13 (1992) 1472. [11] C.P. Wu, C.H. Zhou and EX. Li, Experiments of Polymer Chemistry, Anhui Science and Technology, Hefei, China, 1989, p. 272. [12] B.L. He and X.B. Zhao, React. Polymers, 18 (1992) 229.