1464
Ind. Eng. Chem. Res. 1993,32, 1464-1470
Simple Introduction of Sulfonic Acid Group onto Polyethylene by Radiation-Induced Cografting of Sodium Styrenesulfonate with Hydrophilic Monomers Satoshi Tsuneda, Kyoichi Saito,’ and S h i n t a r o Furusaki Department of Chemical Engineering, Faculty of Engineering, University of Tokyo, Hongo, Tokyo 113, Japan
T a k a n o b u Sugo and Keizo M a k u u c h i Takasaki Radiation Chemistry Research Establishment, Japan Atomic Energy Research Institute, Takasaki, Gunma 370-12, Japan
The sulfonic acid (S03H) group was readily introduced into a polyethylene (PE) membrane by radiation-induced cografting of sodium styrenesulfonate (SSS) with hydrophilic monomers such as acrylic acid (AAc) and hydroxyethyl methacrylate (HEMA). The density of SSS grafted onto the PE membrane was determined as a function of molar ratio of hydrophilic monomer to SSS in the monomer mixture. Immersion of the electron-beam-irradiated PE membrane into the mixture of SSS and HEMA for 5 h a t 323 K provided the S 0 3 H density of 2.5 mol/kg of the H-type product. Introduction Applications of ion-exchange resins include production of pure water, softening of hard water, recovery of metal ions, purification of bioproducts, and catalytic enhancement of hydrolysis. The matrix of conventional ionexchange resins consists of a copolymer of styrene (St) and divinylbenzene (DVB). This matrix was chemically modified to add the ion-exchange moieties. For example, the sulfonicacid group, as a strongly acidic cation-exchange group, can be introduced into the matrix cross-linked with DVB under considerably drastic reaction conditions, e.g., long-period immersion of the matrix polymer in concentrated sulfuric acid or chlorosulfuric acid at an elevated temperature (Wheaton and Lefevre, 1981; Albright and Yarnell, 1987). These preparation schemes induce deterioration of physical strength and emission of polymer debris. In addition, a highly cross-linked matrix with chemical and physical endurable strength prevents us from preparing an arbitrary shape of ion exchanger. We have thus far used ion-exchange beads or ion-exchange membranes based on the St-DVB copolymer matrix. Radiation-induced graft polymerization is superior to other grafting techniques such as those using plasma, light, and chemicals for the following reasons: (1) the high density of the electron beam or y-rays can create a large amount of radicals of arbitrary shapes and qualities of the polymer uniformly over the entire sample and (2) the use of the preirradiation method enables us to separate the two processes of irradiation and graft polymerization, which facilitates commercial use. This technique has been commercialized for the production of ion-exchange membranes as a separator of batteries (Ishigaki et al., 1981) and hydrophilized hollow-fiber membranes for microfiltration of protein solutions (Kim et al., 1991a,b). A chelating porous membrane capable of efficientlycollecting a trace amount of cobalt ions from ultrapure water has been tested for practical use in an atomic power plant (Tsuneda et al., 1991; Yamagishi et al., 1991; Konishi et al., 1992). A sulfonic-acid-group-containingion exchanger can be prepared by grafting of sodium styrenesulfonate (SSS, CHyCHCBH&303Na) onto polyethylene, polypropylene, or polytetrafluoroethylene so as to fulfill a requisite for shape, e.g., film, nonwoven fabric, fiber, or bead. Preparation conditions in this study are milder than those
of conventional sulfonations because irradiations of electron beams or y-rays provide a sufficient density of the radicals for initiation of graft polymerization. Shkolnik and Behar (1982)have reported the difficulties in direct grafting of SSS onto a high-density polyethylene (HDPE) film by radiation-induced grafting because of low accessibility of hydrophilic SSS to hydrophobic HDPE. However, they have demonstrated that the grafting rate of SSS could be enhanced by adopting a two-step grafting technique: acrylic acid was pregrafted onto the HDPE film, and then SSS was polymerized after another irradiation. Other combinations between prehydrophilized trunk polymers and SSS have not been described. In general, two-step grafting is practically disadvantageous because repeated irradiations require additional procedures and costs. In this study, we propose one-step grafting of SSS with hydrophilic monomers onto a polyethylene hollow-fiber membrane to readily introduce the sulfonic acid group. Introduction of SSS into trunk polymers was classified into three modes, as illustrated schematically in Figure 1: (1)one-step grafting/one monomer, (2) two-step grafting/ two monomers, and (3) one-step graftinghwo monomers. Two-step grafting means that irradiation and subsequent grafting are repeated. The two monomers are SSS and another monomer. The purposes of our study were 3-fold: (1)to clarify the role of hydrophilicity of the trunk polymer in introduction of SSS, (2) to elucidate the effect of the pregrafted polymer branches on the SSS grafting in two-step grafting, and (3) to establish the preparation method of one-step introduction of SSS. Experimental Section Materials. Porous polyethylene (PE) hollow-fiber membrane (Asahi Chemical Industry Co., Ltd.)and porous cellulosetriacetate (CTA) flat-sheet membrane (Fuji Film Co., Ltd.) were used as trunk polymers for grafting. Table I summarizes the physical properties of these trunk polymers. A 47-mm-diameter flat-sheet membrane and 5-em-long hollow-fiber membrane were used. The following seven monomers of reagent grade were used without further purification: acrylic acid (AAc,C H d H C O O H ) , acrylonitrile (AN, CHz=CHCN), glycidyl methacrylate
0888-5885/93/2632-1464$04.00/00 1993 American Chemical Society
Ind. Eng. Chem. Res., Vol. 32, No. 7, 1993 1465 €5
One-stepgrafting / one monomer
irradiation grafting trunk polymer
EB
Two-step grafting / two monomers
EB
-I+&
?%%
A&
Irradiation grafting Irradiation grafting
irradiation grafting trunk polymer
E?
One-step grafting / two monomers (Co-grafting)
L,
irradiation araftina trunk polymer
-
-
Figure 1. Schematic illustrations of three grafting modes. (0) hydrophilic monomer: ( 0 )sulfonic-acid-groupcontaining monomer; EB = electron beam. Table I. Physical Properties of T r u n k Polymers
PE shape hollow fiber size i.d. 1.95 mm 0.d. 3.01 mm average pore diameter 0.34 pm porosity 71% degree of crystallinity 55% 0 Determined by differential scanning calorimetry (DSC). CTA flat sheet diameter 47 mm thickness 0.135 mm 0.22 pm 75% 5%
(GMA, CHZ=CCH~COOCHZCHOCHZ),hydroxyethyl methacrylate (HEMA, CHZ=CCH~COOCH&HZ~H), methyl methacrylate (MMA, CHZ=CCH~COOCH~),vinyl acetate (VAc, CHZ=CHOCOCH~), and sodium styreneN ~ ) . water sulfonate (SSS,C H ~ H C G H ~ S O ~Deionized and technical-grade methanol were used as solvents. Graft Polymerization. The preirradiation grafting technique was adopted in this study. A prescribed dose of electron beam (EB) was irradiated onto the trunk polymer a t an ambient temperature under a nitrogen atmosphere. Irradiation was performed by using a cascadetype accelerator with a beam energy of 1.5MeV and electric current of 1mA. The total dose was 200 kGy (=20 Mrad). The irradiated trunk polymer was exposed to air for about 3 min before graft polymerization to transfer it to a glass ampule. In liquid-phase grafting (Yamagishi et al., 1991), irradiated trunk polymer was immersed in the glass ampule containing monomer previously deaerated by bubbling nitrogen gas. Immersion of irradiated porous PE hollowfiber membrane in methanol for 5 min and subsequent replacement of methanol with water allowed an aqueous monomer solution to invade the pores and initiate the graft polymerization. In vapor-phase grafting (Saito et al., 19891, irradiated trunk polymer was contacted with vapor of a monomer previously deaerated by thawing the monomer three times. After grafting, the membranes were soaked in each wash for 1h at 323 K three times in order to remove the residual monomer and homopolymer, and then were dried under reduced pressure. Table I1 summarizes the reaction conditions and washings of the three modes of graft polymerization. 1. One-Step Grafting/One Monomer. The density of SSS grafted onto the CTA and P E membranes was determined from the measurement of salt-splitting capacity of the resultant membrane: the membrane was soaked in 1M HClto convert the Na-form into the H-form, and then washed repeatedly with water. The amount of HC1 liberated by immersion of the H-form membrane in
Table 11. Reaction Conditions and Washings of Radiation-Induced Grafting of SSS onto P E and CTA. dose,
monomer phase* concn solvent One-Step Grafting/One Monomer 200 L 1M water
kGy
sss
323
water
Two-step Grafting/TwoMonomers
AAC-sss 1st 2nd AN-SSS 1st 2nd GMA-SSS 1st 2nd HEMA-SSS 1st 2nd MMA-SSS 1st 2nd VAc-SSS
100 100
L L
4wt% 1M
water water
323 323
water water
100 100
v L
100% 1M
water
313 323
water
100 100
L L
1Ovol 75 1M
methanol water
313 323
water
100 100
L L
2wt% 1M
water water
323 323
water water
100 100
v L
1M
water
313 323
water
200 100
v
100%
L
1M
water
313 323
water
50
L L
20wt %
water water
343 343
water water
One-Step Grafting/TwoMonomers (Cografting) 200 L 1M SSS; water 323 0.1-10 M
water
1st
2nd AAc-SSSC 1st 2nd AAc/SSS
temp, K wash
100
100%
lOwt %
DMF
AAC
HEMA/SSS
200
L
1MSSS; 0.1-5 M HEMA
water
323
water
Abbreviation of monomers: AAc = acrylic acid, AN = acrylonitrile, GMA = glycidyl methacrylate, HEMA = hydroxyethyl methacrylate, MMA = methyl methacrylate, VAc = vinyl acetate, SSS = sodiumstyrenesulfonate. L, liquid phase, V, vaporphaee. Shkolnik and Behar (1982).
5 wt 7% aqueous NaCl solution was determined by titration with 1/50 M NaOH, and was converted into the density of the sulfonic acid (S03H) group by dividing by the weight of the starting membrane. The amount of the S03Hgroup calculated from the weight gain agreed well with that of the S03H group determined by titration. 2. Two-step Grafting/Two Monomers. First, AAc, AN, GMA, HEMA, MMA, or VAc was pregrafted onto the irradiated PE hollow-fiber membrane. Of these, GMApregrafted and VAc-pregrafted P E membranes were hydrolyzed with 0.5 M HzS04 and 1M NaOH, respectively,
1466 Ind. Eng. Chem. Res., Vol. 32, No. 7, 1993 One-step grafting I one monomer cn
Y
4
6 - trunk polymer
vr vr vr
4-
U
8
6
2-
p 8
0
2
6
4
Reaction time [h] Figure 2. Time course of SSSgrafting onto P E and CTA membranes. CTA = cellulose triacetate; PE = polyethylene; SSS = sodium styrenesulfonate. Two-step grafting / two monomers pregrafted monomer
. Y
A
Y
v
v,
VAc(H)
A
AAC 0 --V-.AAC (Shkolnika
5
0
MMA HEMA
10
15
Density of pregrafted polymer branches [mol / kg-TP]
Figure 3. Density of SSS grafted onto PE modified with various densities of pregrafted polymer branches. AAc = acrylic acid; AN = acrylonitrile;GMA(H)= hydrolyzedglycidylmethacrylate; HEMA = hydroxyethyl methacrylate; MMA = methyl methacrylate; VAc(H) = hydrolyzed vinyl acetate. ii:
7-
. ."I
Y
C
n
c
61
I
1
I
0 radical on PE trunk chain A radical on poly-AAc graft chain
X
2
0
20
40
60
Density of grafted AAc [mol/kg-TP]
Figure 4. Radical concentrations on the polyAAc graft chain and P E trunk chain. AAc = acrylic acid; PE = polyethylene.
into diol-group- and alcoholic-hydroxyl-group-containing membranes. After pregrafting and subsequent hydrolysis, the membrane was repeatedly washed and then was dried and weighed. The density of the pregrafted polymer branches per kilogram of trunk polymer, q, can be calculated from the weight changes as follows.
[(Wi - Wo)/Mml/Wo
(1) where WOand WI are the weights of the starting and pregrafted membranes, respectively. M m is the molecular weight of the monomers except for GMA and VAc. M m is 142 18 or 86 + 18 - 60 for hydrolyzed GMA or hydrolyzed VAc, respectively, where the factors 142, 86, =
+
0
20
40
60
Density of grafted AAc or AN [mol / kg-TP] Figure 5. Swelling ratio vs density of polyAAc and polyAN graft chains. AAc = acrylic acid; AN = acrylonitrile..
60, and 18 correspond to the molecular weights of GMA, VAc, acetic acid, and water, respectively. Second, prior to another grafting, pregrafted membrane was dried. After a second irradiation, SSS was grafted onto the membrane. The density of SSS grafted can be determined from the measurement of salt-splitting capacity. 3. One-Step Grafting/Two Monomers. SSS was cografted with AAc or HEMA by immersing irradiated P E hollow-fiber membrane in a mixture of AAc and SSS or HEMA and SSS. The concentration of SSS was maintained at 1M. The molar ratio of AAc or HEMA to SSS ranged from 0.1 to 10 or from 0.1 to 5, respectively. The molar ratio of SSS initially in the liquid to SSS finally grafted onto the membrane was over 100. The total amount of the grafted polymer branches can be calculated by the weight gain. The amount of AAc or BEMA grafted was obtainable by subtracting the polySSS amount from the total amount. ESR Measurement. To assess the radical species involved in one-step grafting, the ESR spectra of the irradiated polymer were measured by means of an ESR spectrometer (JES-FESX, JEOL). After irradiation a t a dose of 200 kGy and subsequent exposure to the air for 3 min, the PE or CTA membrane was sealed in an ESR tube with a silicon stopper. Here, intentional 3-min exposure to air before ESR measurement was consistent with the graft polymerization procedure, and was necessary for determining the initial concentration of the radicals contributing to the graft polymerization. The tube was placed in a TEoll cylindrical cavity. A microwave of X-band (9-GHz band) was applied at 10-3 mW and 100kHz frequency of magnetic field modulation. All measurements were performed at 77 K. The ESR spectra of the AAc-pregrafted PE membrane were also measured in order to specify the radicals contributing to two-step grafting. Here, ESR measurement included the following procedures as performed in the graft polymerization: (1)irradiation of EB on the AAcpregrafted P E membrane at dose of 100kGy, (2) immersion of the membrane in methanol for 5 min and replacement of methanol with water (methanol treatment), and (3) drying under reduced pressure for 6 h. The resulting ESR spectra represent two radicalspecies: radicals on the trunk polymer (PE) chain and radicals on the graft polymer (polyAAc) chain. The procedures for separating the radicals from each other are discribed in the Appendix. Determination of Swelling Ratio. After methanol treatment of dried AAc- and AN-pregrafted PE membranes, the inner and outer diameters of the hollow-fiber membrane were measured with a microscope, and the
Ind. Eng. Chem. Res., Vol. 32, No. 7,1993 1467
grafting of SSS ( 0 ) in water
e
a pregrafting of hydrophilic monomer (0)
-...I.J
1 .
hvdiophobic monomer ( A )
grafting of SSS ( 0 ) in water
*
$I
(2-b)
* (2-C)
(24
Figure6. Schematicillustrations of enhancement of SSS grafting hy prehydrophilization of PE. (a)PE matrix consistsof crystallites (shaded
area) and amorphous domain (unshaded area). (1-h) Hydrophilic monomer (0)was pregrafted. Pregraft chains stem from the surface of the crystallites in preirradiation technique. (1-c) Hydrophilic pregraft chain swells in an aqueous SSS solution. Swelling enhances the access of SSS in amorphous domain to the radical site. (1-d)SSS was graftsd. ( 2 4 Hydrophobic monomer (A)was pregrafted. ( 2 4 Hydrophobic pregraft chain does not swell in an aqueous SSS solution. The access of SSS in amorphous domain is restricted. (2-d) SSS was not grafted.
length was measured with a scale in a wet state. Swelling ratio was defined as follows: swelling ratio = VJ Vd (2) where v d and V, designate the volume of the membrane in the dry and wet states, respectively. Results and Discussion One-Step Grafting/One Monomer. A graft chain can grow from the radicals formed on a trunk polymer by irradiation. Species and concentrations of the radicals formed on cellulose triacetate (CTA) and polyethylene (PE) membranes by electron-beam (EB) irradiation could be determined by analysis of the ESR spectra. The radical concentrations of the CTA and PE membranes were 2.6 X 1014 and 1.1 X 10l6 spins/kg of the trunk polymer, respectively. Contact of the radicals with the air induces the transformation to a relatively short-lived peroxy radical. Oxygen in the air can easily diffuse into the amorphous domain of the CTA matrix because the CTA matrix has a lower crystallinity (5%) and smaller crystallites than the PE matrix. By contrast, PE with a higher crystallinity (55%) can maintain alkyl and allyl radicals in the larger crystallites (Uezu et al., 1992). Figure 2 shows the density of sodium styrenesulfonate (SSS) grafted onto PE and CTA membranes as a function of reaction time. Although the initial radicalconcentration of PE was 40-fold higher than that of CTA, the density of SSS grafted onto the PE membrane was only one-fifth of that grafted onto the CTA membrane at 5 h of reaction time. In this preparation mode, lower accessibility of hydrophilic SSS to hydrophobic PE than to hydrophilic CTA resulted in a lower grafting rate of SSS on P E than on CTA. Two-step Grafting/Two Monomers. We systematically examined the positive effect of the pregrafting of hydrophilic monomer onto the PE membrane on the
subsequent grafting rate of SSS. Shkolnik and Behar (1952) have proposed two-step grafting in order to induce SSS into PE. However, the pregrafted polymer was only polyAAc, and the density of SSS has not been sufficient for its practical use as an ion exchanger. In this study, the following four kinds of hydrophilicpolymer branches were introduced into the P E membrane as an inductive graft polymer: polyAAc, polyHEMA, polyGMA(H), and polyVAc(H). The last two pregrafted polymer branches were obtained by hydrolysis of polyGMA and polyVAc, respectively. For comparison, the two hydrophobic polymer branches of polyAN and polyMMA were also pregrafted. Figure 3 shows the density of SSS grafted onto the six variations of pregrafted PE membrane. Hydrophilic polymer branches enhancedthegraftingrateofSSS,while hydrophobic polymer branches had aslight negative effect. This can be explained by two factors: (1)the change in the species and concentrations of the radicals, which leads to an increase in initiation of graft polymerization, and (2) the change in the polymer structure, which influences the accessibility of the SSS monomer to the radicals. First, we determined the species and concentrations of the radicals formed on the AAc-pregrafted PE membrane by another irradiation of EB at a dose of 100 kGy and subsequent methanol treatment. The radicals formed on the trunk PE chains and the radicals formed on the polyAAc graft chains could be separated from each other on the basis of the integral form of ESR spectra. Figure 4 shows the radical concentrations as a function of the density of polyAAc graft chains. With an increasing density of polyAAc graft chains pregrafted onto the PE membrane, the concentration of the radical on the trunk polymer PE chains gradually decreased, while that of the radical on the polyAAc chains remained constant. Invasion of the grafted polymer branches into the polymer matrix allowed oxygen in the air to diffuse to the radical site and produce the peroxyradical, which decays instantaneously.
1468 Ind. Eng. Chem. Res., Vol. 32, No. 7, 1993
Second, Figure 5 shows the swelling ratio of the AAcand AN-pregrafted PE membrane. The swelling ratio, indicative of hydrophilicity, increased with an increasing density of polyAAc graft chain, but remained at a constant value of 1with an increasing density of polyAN graft chain. As a result, invasion of hydrophilic polymer branches into the amorphous domain by pregrafting allowed the PE matrix to swell in an aqueous medium and enhance the grafting. Figure 6 shows the schematic illustrations to explain the mechanisms of the two-step grafting. The PE matrix consists of crystallites and amorphous domain. Since pregrafted hydrophilic polymer chains swell in an aqueous SSS solution, the access of SSS in amorphous domain to the radical site is enhanced, resulting in an increase of the grafting rate. By contrast, pregrafted hydrophobic polymer chains restrict the access of SSS. One-Step Grafting/Two Monomers. The two-step grafting technique is not feasible because of the additional procedures and costs of two rounds of irradiation. Here, we propose an alternative means of introducing SSS into a hydrophobic trunk polymer: SSS and hydrophilic monomer such as AAc and HEMA can be cografted onto the PE membrane. The cografting technique has been mainly applied to the design of biocompatible materials with optimal hydrophilic-hydrophobic balance (Uenoyama and Hoffman, 1988; Chen et al., 1992; Sreenivasan and Rao, 1992). Parts a and b of Figure 7 show the densities of the AAC and SSS cografted chain, and the HEMA and SSS cografted chain, respectively, as a function of reaction time in cograft polymerization. A significant effect was observed, compared to SSS grafting without AAc and HEMA: for example, the maximum density of SSS cografted with AAc was 9.5 mol/kg of trunk polymer, which was 10-fold higher than that of SSS grafted without AAc. This density of SSS is converted to the total ion-exchange capacity of 2.5 mol/kg of the H-type product, which is equivalent to that of a commercially available strongly acidic cation-exchange bead and membrane. The conventional preparation scheme of the SO3H-group-containing materials consists of St-DVB copolymerization, sulfonation, and conditionings, where the polymer endures drastic reaction conditions such as long-period contact with concentrated sulfuric acid a t an elevated temperature (Wheaton and Lefevre, 1981;Albright and Yarnell, 1987). On the other hand, the novel scheme proposed here includes irradiation of EB onto a P E membrane, immersion in the mixture of AAc and SSS or HEMA and SSS in a mild reaction condition, and conditioning. The density of SSS grafted was compared between AAcI SSS and H E M A W S combinations by varying the molar ratio of AAc or HEMA to SSS in the monomer mixture. Parts a and b of Figure 8 show the density of SSS grafted at a grafting time of 5 h vs the molar ratio of AAc and HEMA to SSS, respectively. A distinct difference regarding the SSS density was observed: a curve for the AAcISSS combination had a maximum value of 7.1 mol/ kg of the trunk polymer at a molar ratio of 1/3, while a curve for the HEMA/SSS combination leveled off a t 7.4 mol/kg over the molar ratio of 1/10. HEMA is also used for cografting with the anion-exchange-group-containing monomer. By contrast, AAc is not suitable because the polyAAc chain forms a complex with the polyanionexchange-group-containingchain. Since the polyAAc graft chain functions as a weakly acidic cation-exchange group, it will perform auxilliary work such as metal collection in neutral pH ranges.
E !.
0
sss
SSS 1 M
z -E, P
g! 6
10
SSS (without AAc)
r
15 I-
A HEMA
HEMA 0.1M
-J
$
6
5
c
I
5
10
Reaction time [h]
(b)
Figure 7. Cograftingrate of SSS onto PE membrane. (a) AAcISSS combination; (b) HEMAISSS combination. AAc = acrylic acid; HEMA = hydroxyethyl methacrylate; SSS = sodium atyrenesulfonate.
At present, characterization of the grafted polymer branches prepared by radiation-induced cografting, e.g., in terms of the length and density of the graft chain and the composition of the cograft chain, is very difficult. However, practically speaking, the novel method proposed here is promising from the standpoint of simple preparation of the ion-exchange materials.
Conclusions A novel and simple preparation method for sulfonicacid-group-containing material was proposed as an alternative to sulfonation of conventional styrene (St)divinylbenzene (DVB) matrix. Sodium styrenesulfonate (SSS) was grafted in the liquid phase onto electron-beamirradiated polyethylene (PE). 1. Hydrophilic SSS could be easily grafted onto the hydrophilic CTA membrane. 2. SSS could be grafted onto PE membrane carrying pregrafted polymer branches with monomer units of AAc, HEMA, hydrolyzed GMA, and hydrolyzed VAc. 3. SSS could be readily cografted with HEMA and AAc by immersing the irradiated PE membrane in an aqueous solution of AAc/SSS and HEMA/SSS mixtures. The density of the S03H group of the resultant membrane amounted to 2.5 mol/kg of the H-type product, which is equivalent to that of a commercially available cationexchange membrane. These cografting procedures enabled us to introduce a hydrophilic monomer such as SSS into P E under relatively
Ind. Eng. Chem. Res., Vol. 32, No. 7,1993 1469 i
7P,
. Y
AAc 0.1-10 M
0 sss
&
SSS
1M
E,
2
B
6
Molar ratio of AAc to SSS in monomer mixture [ - ]
4
a,
I
'
,
. .'"'I
. .
' ' ""I
One-step grafting / two monomers
A HEMA
HEMA 0.1-5 M
';:& . . ..
.. . pJ ....
EE
..... .:
P,
(4 Molar ratio of HEMA to SSS in monomer mixture [ - ] (b)
Figure 8. Dependence of density of SSS grafted on the membrane
on the molar ratio of hydrophilic monomer to SSS in the monomer mixture. (a) AAc/SSS combination; (b) HEMA/SSS combination. AAc = acrylic acid; HEMA = hydroxyethyl methacrylate; SSS = sodium styrenesulfonate.
mild reaction conditions as compared with those of conventional sulfonation based on a St-DVB matrix. Acknowledgment The authors with to thank Kazuo Toyomoto of the Industrial Membrane Division of Asahi Chemical Industry Co., Ltd., Japan, for his help in providing the starting hollow-fibermembrane. Helpful discussions with Satoshi Tanaka of Nikki Chemical Co., Ltd., Japan, are gratefully acknowledged. We are also grateful to Tsuyoshi Yoshida for designing the schematic illustrations and Jun-ichi Kanno for measuring the ESR spectra. This work was supported by Salt Science Research Foundation. Nomenclature AAc = acrylic acid AN = acrylonitrile CTA = cellulose triacetate DVB = divinylbenzene EB = electron beam GMA = glycidyl methacrylate GMA(H) = hydrolyzed GMA HEMA = hydroxyethyl methacrylate MMA = methyl methacrylate PE = polyethylene SSS = sodium stpenesulfonate St = styrene
Figure 9. ESR spectra of integral form. (a) P E (b) polyAAc; (c) AAc-pregrafted PE. Spectrum a was interposed in spectrum c. TP = trunk polymer VAc = vinyl acetate VAc(H) = hydrolyzed VAc Appendix. Separation of Radicals of PE and Poly-AAc Polyethylene (PE)membrane, poly(acrylicacid) powder, and AAc-pregrafted PE membrane were irradiated by electron beam with a dose of 100 kGy at ambient temperature under a nitrogen atmosphere. Figure 9 shows comparison of the integral forms of ESR spectra. The spectra originating from PE and polyAAc were superimposed on the spectra of AAc-grafted PE. The S k part shown in Figure 9c is assigned to the alkyl radical of PE and does not overlap the peak originating from polyAAc. The intensity of alkyl and allyl radicals of PE can be calculated as 32-fold and 9.5-fold area of the s k part, respectively (Uezu et al., 1992). Therefore, the radicals originating from the polyAAc graft chain of the AAcpregrafted P E were calculated as follows: area(po1yAAc) = total area - (32 + 9.5) [area(Sk)l Literature Cited Albright, R. L.; Yarnell, P. A. Ion-Exchange Polymers. In Encyclopedia of Polymer Science and Engineering;Mark, H. F., Bikales, N. M., Overberger, C. G., Menges, G., Eds.; Wiley: New York, 1987;Vol. 8. Chen, G.; Dose, L.; Bantjes, A. Investigations on Vinylene Carbonate. IV. Radiation-Induced Graft Copolymerization of Vinylene Carbonate and N-Vinyl-N-Methylacetamide onto Polyethylene Films. J. Appl. Polym. Sci. 1992, 45, 853. Ishigaki, I.; Sugo, T.; Senoo, T.; Takayama, S.; Machi, S. Synthesis of Ion-Exchange Membrane by Radiaton Grafting of Acrylic Acid onto Polyethylene. Radiat. Phys. Chem. 1981, 18,899.
1470 Ind. Eng. Chem. Res., Vol. 32, No. 7, 1993 Kim, M.; Saito, K.; Furusaki, S.; Sugo, T.; Okamoto, J. Water Flux and Protein Adsorption of a HollowFiber Modified with Hydroxyl Groups. J. Membr. Sci. 1991a, 56,289. Kim, M.; Saito, K.; Furusaki, S.; Sugo, T.; Ishigaki, I. Protein Adsorption Capacity of a Porous Phenylalanine-ContainingMembrane Based on a Polyethylene Matrix. J. Chromatogr. 1991b, 586,27. Konishi, S.;Saito, K.; Furusaki, S.; Sugo, T. Sorption Kinetics of Cobalt in Chelatine Porous Membrane. Ind. Enp. - Chem. Res. 1992,31, 2722. Saito, K.; Ito, M.; Yamagishi, H.; Furusaki, S.; Sugo, T.; Okamoto, J. Novel Hollow-Fiber Membrane for the Removal of Metal Ion during Permeation: Preparation by Radiation-Induced Cograftiig of a Cross-LinkingAgent withbactive Monomer. Ind. Eng. Chem. Res. 1989, 28, 1808. Shkolnik, S.;Behar, D. Radiation-Induced Grafting of Sulfonates on Polyethylene. J. Appl. Polym. Sci. 1982, 27, 2189. Sreenivasan, K.; Rao, K. V. C. Studies on the Radiation-Induced Graft Copolymerization of Mixtures of N-Butyl Acrylate and 2-Hydrosyethyl Methacrylate on Polyurethane. I. Synthesis and Characterization. J. Appl. Polym. Sci. 1992, 44, 1703. I
Tsuneda, S.; Saito, K.; F~uusaki,S.; Sugo, T.; Okamoto,J. Metal Collection Using Chelating Hollow Fiber Membrane. J. Membr. Sci. 1991, 58,221. Uenoyama, S.; Hoffman, A. S. Synthesis and Characterization of Acrylamide-N-IsopropylAcrylamideCopolymerGrafts on Silicone Rubber Substrates. Radiat. Phys. Chem. 1988,32,606. Uezu, K.; Saito, K.;Furueaki, S.; Sugo, T.; Ishigaki, I. Radicals Contributing to Preirradiation Graft Polymerization onto Porous Polyethylene. Radiat. Phys. Chem. 1992,40, 31. Wheaton, R. M.; Lefevre, L. J. Ion Exchange. In Encyclopedia of Chemical Technology;Mark, H. F., Othmer, D. F., Overberger, C. G., Seaborg, G. T., Eds.; Wiley: New York, 1981; Vol. 13. Yamagishi, H.; Saito, K.; Furusaki, S.; Sugo,T.; Ishigaki, I. Introduction of a High-Density Chelating Group into a Porous Membrane without Lowering the Flux. Ind. Eng. Chem. Res. 1991,30, 2234. Receiued for reuiew October 14, 1992 Accepted March 30, 1993
