Synthesis and gas permeability of membranes of Poly(vinyl ether)s bearing oxyethylene segments

Synthesis and gas permeability of membranes of Poly(vinyl ether)s bearing oxyethylene segments

Polymer 53 (2012) 1659e1664 Contents lists available at SciVerse ScienceDirect Polymer journal homepage: www.elsevier.com/locate/polymer Synthesis ...

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Polymer 53 (2012) 1659e1664

Contents lists available at SciVerse ScienceDirect

Polymer journal homepage: www.elsevier.com/locate/polymer

Synthesis and gas permeability of membranes of Poly(vinyl ether)s bearing oxyethylene segments Toshikazu Sakaguchi*, Masako Ohashi, Kazuya Shimada, Tamotsu Hashimoto Department of Materials Science and Engineering, Graduate School of Engineering, University of Fukui, Bunkyo, Fukui 910 8507, Japan

a r t i c l e i n f o

a b s t r a c t

Article history: Received 15 December 2011 Received in revised form 16 February 2012 Accepted 19 February 2012 Available online 24 February 2012

Cationic copolymerizations of vinyl ether monomers [2-methoxyethyl vinyl ether: MOVE, 2-(2methoxyethoxy)ethyl vinyl ether: MEEVE, 2-adamantyl vinyl ether: AdVE, 2-(2-vinyloxyethoxy)ethyl methacrylate: VEEM] were performed to obtain three types of vinyl ether copolymers [poly(MOVEAdVE)s, poly(MEEVE-AdVE)s, and poly(MEEVE-VEEM)s] with different composition rates. Poly(MOVEAdVE) and poly(MEEVE-AdVE) obtained at monomer feed ratio of 1:1 exhibited the glass transition temperatures (Tg) of 55 and 28  C, respectively, but the Tg’s of copolymers were near or lower than room temperature when the feed ratio of AdVE decreased. Poly(MOVE-AdVE)s and poly(MEEVE-AdVE) with Tg’s above room temperature afforded free-standing membranes by casting them from toluene solutions. They exhibited relatively high CO2 permeability and high CO2/N2 separation factors (P(CO2) ¼ 22e36 barrers, P(CO2)/P(N2) ¼ 19e40). The Tg’s of poly(MEEVE-VEEM)s were very low and around 70  C irrespective of the difference of monomer feed ratio. Methacrylate groups in poly(MEEVE-VEEM)s partially reacted under heating to give crosslinked polymer membranes. The crosslinked membranes showed high CO2/N2 selectivity, especially the poly(MEEVE-VEEM) membrane possessing the highest ratio of MEEVE exhibited high CO2 permeability and high selectivity (P(CO2) ¼ 120 barrers, P(CO2)/ P(N2) ¼ 55). Ó 2012 Elsevier Ltd. All rights reserved.

Keywords: Poly(vinyl ether) Membrane Gas permeability

1. Introduction Gas separation by polymeric membranes is considered to be an effective technology because of energy efficiency, low operating costs, and simple procedure [1,2]. Recently, the separation of CO2 from N2 becomes important because increase of CO2 concentration in the atmosphere is thought to contribute to global warming [3]. Thus, the development of novel membranes with high CO2 separation performance is desired, but there is currently no material which exhibits enough high selectivity of CO2 over N2. One approach to develop membranes with high CO2/N2 selectivity is to enhance CO2 solubility in membrane matrix. Freeman et al. proposed that solubility selectivity of CO2 over light gases such as H2 and N2 can be improved by introduction of polar groups into polymer membranes because CO2 molecule has a quadrupolar moment and interacts favorably with polar groups [4]. Especially, polar ether oxygens have appropriate polarity and highly favorable interaction with CO2 molecules. Therefore, materials with ether oxygens appear to be attractive candidates for CO2 separation membranes. * Corresponding author. Tel.: þ81 776 27 9779; fax: þ81 776 27 8767. E-mail address: [email protected] (T. Sakaguchi). 0032-3861/$ e see front matter Ó 2012 Elsevier Ltd. All rights reserved. doi:10.1016/j.polymer.2012.02.036

Poly(ethylene oxide) [PEO] membrane had been studied and found to exhibit relatively high CO2 selectivity [5]. PEO membrane, however, showed rather low CO2 permeability coefficient of 12 barrers because of its high crystallinity. If a PEO membrane is wholly amorphous, the permeability coefficient is estimated to become 140 barrers [5]. Therefore, a wide variety of polymers bearing low-molecular-weight amorphous PEO have been studied for CO2 separation from light gases [6e24]. For example, the crosslinked PEO membranes prepared from poly(ethylene glycol) diacrylate exhibit high CO2 permeability and CO2 selectivity [6e14]. PEO-segmented poly(ether imide)s exhibit excellent CO2 permselectivity, and poly(ether imide) bearing wholly amorphous PEO shows high CO2 permeability and high CO2/N2 selectivity [15e17]. Polyesters [18], polyamides [19e21], polyurethanes [22], polyacetylenes [23], and poly(phenylene)s [24] containing PEO segments have also been reported to exhibit high CO2 permselectivity. Based on these previous studies, we considered that poly(vinyl ether)s bearing oxyethylene segments as side chains are interesting polymers for CO2 separation materials. Such poly(vinyl ether)s are wholly amorphous and contain high oxyethylene moieties. In addition, the flexible side chains of oxyethylene segments would promote gas diffusion in polymer matrix.

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In the present study, a series of poly(vinyl ether)s bearing oxyethylene segments as side chains have been synthesized to develop new materials for CO2 separation membranes. Poly(MOVE) and poly(MEEVE) are sticky liquid because of their low Tg’s [25], and hence, their free-standing membranes can not be obtained. Poly(AdVE) has high Tg of 180  C [26], and its membrane exhibits the highest gas permeability among poly(vinyl ether)s reported previously [27]. Poly(MOVE-AdVE)s and poly(MEEVE-AdVE)s were synthesized by cationic copolymerization of MOVE and MEEVE with AdVE, respectively. Their membranes could be prepared by solution casting.Poly(MEEVE-VEEM)s were also synthesized by copolymerization of MEEVE with VEEM, and their crosslinked membranes could be prepared by thermal crosslinking of their methacrylate groups. Gas permeability and selectivity of their membranes were investigated(Schemes 1and 2). 2. Experimental 2.1. Measurements The molecular weight distributions (MWDs) of polymers were measured by gel permeation chromatography (GPC) in chloroform (at a 1.0 mL/min flow rate) at 40  C on a Shimadzu LC-10AD chromatograph equipped with four polystyrene gel columns (Shodex K-805L  1 and K-804L  3) and a Shimadzu RID-6A refractive index detector. The number-average molecular weight (Mn) and polydispersity ratio [weight-average molecular weight/numberaverage molecular weight (Mw/Mn)] were calculated from chromatograms based on a polystyrene calibration. 1H (500 MHz) NMR spectra were recorded on Jeol LA-500 instrument in CDCl3 at room temperature. Differential scanning calorimetry (DSC) was

performed with Rigaku Thermo Plus DSC 8230L with 5  C/min heating and cooling rates. During the measurement, the sample was purged by nitrogen gas. Glass transition temperature (Tg) was defined as the temperature of midpoint of the change in heat capacity on second heating scan. Gas permeability coefficients were measured with a Rikaseiki K-315-N gas permeability apparatus at 25  C under 1 atm upstream pressure using dry gases. The permeability coefficient P expressed in barrer unit (1 barrer ¼ 1010 cm3(STP) cm cm2 s1 cmHg1) was calculated from the slope of the steady-state line. 2.2. Materials 2-Methoxyethyl vinyl ether (MOVE), 2-(2-methoxyethoxy)ethyl vinyl ether (MEEVE), and 2-adamanthyl vinyl ether (AdVE) were supplied by Maruzen Petrochemical (Tokyo, Japan) and distilled under reduced pressure over calcium hydride. 2-(2-Vinyloxyethoxy)ethyl methacrylate (VEEM) was supplied by Nippon Shokubai (Osaka, Japan), dried over sodium sulfate, and distilled over tert-butylcatechol under reduced pressure. Isobutyl vinyl ether-acetic acid adduct (CH3CH(OiBu)OCOCH3: IBEA) was synthesized by treatment of isobutyl vinyl ether with acetic acid at 60  C and purified by distillation [28]. Et1.5AlCl1.5 (1.82 M solution in toluene) was commercially obtained from Aldrich and used without further purification. Toluene (solvent for polymerization) was distilled twice over calcium hydride. 2.3. Copolymerization Copolymerizations of vinyl ethers were carried out under a dry nitrogen atmosphere in a glass tube equipped with a three-way

Scheme 1. Copolymerization of vinyl ether monomers (MOVE, MEEVE, AdVE, VEEM).

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Scheme 2. Thermal crosslinking of poly(MEEVE-VEEM)s.

stopcock, which was baked at ca. 400  C on a heat gun just before the reaction. The toluene solutions of cationogen (IBEA) and Lewis acid (Et1.5AlCl1.5) were prepared in the separate tubes. The solution of IBEA was supplied to a monomer solution containing internal standard for GC (heptane or tetrahydronaphthalene). Then, the solution of Et1.5AlCl1.5 was added to the mixture. Polymerization was terminated by the addition of an excess amount of methanol (2.0 mL) containing a small amount of aqueous ammonia. Monomer conversion was determined from its residual concentration measured by gas chromatography. To work-up the polymers, the reaction mixture was diluted with CH2Cl2 and washed with 0.1 mol/L hydrochloric acid and 10 wt% aqueous sodium chloride in this order. The organic solution was concentrated by rotary evaporator and the resultant polymers were isolated by precipitation into a large excess of methanol or hexane. 2.4. Membrane preparation Free-standing membranes of poly(MOVE-AdVE)s and poly(MEEVE-AdVE) (thickness ca. 100e200 mm) were prepared by casting polymer solution in toluene (concn 1.0e1.5 wt%) onto a Teflon plate. The plate was covered with a glass vessel to slow down solvent evaporation at room temperature (ca. 3e5 days). After a membrane was formed, the membrane was peeled off, and it was dried at room temperature under reduced pressure for 24. All the obtained membranes were colorless and transparent, and they were found to be amorphous from DSC measurement. Crosslinked membranes of poly(MEEVE-VEEM)s were prepared by solution casting followed by heating. Poly(MEEVE-VEEM) was dissolved in toluene to prepare a 1.5 wt% casting solution. The solution was cast onto a Teflon plate covered with a glass vessel. The solvent was slowly evaporated at room temperature under atmosphere pressure for 5 day. After evaporation of solvent, the rubbery polymer in Teflon plate was placed in an oven at 60  C for 24 h. Then, the oven was turned off and the formed membrane was cooled to room temperature. The membrane was dried at room temperature under reduced pressure for 24 h. All the crosslinked poly(MEEVEVEEM) membranes were colorless, transparent, and amorphous as same as poly(MOVE-AdVE) and poly(MEEVE-AdVE) membranes. 3. Results and discussion 3.1. Copolymerization The copolymerizations of vinyl ethers were carried out with IBEA/Et1.5AlCl1.5 in toluene at 0  C. The IBEA/Et1.5AlCl1.5-initiated polymerization is known to produce poly(vinyl ether)s with relatively narrow molecular weight distribution [29]. The results of copolymerization of MOVE with AdVE are summarized in Table 1. When the reaction was performed at the initial molar ratio of MOVE:AdVE ¼ 1:1, both monomer conversions reached up to 100% in 24 h and the copolymer [poly(MOVE-AdVE)(1:1)] was obtained,

whose Mn was 40,000. The copolymerization at the 2:1 initial molar ratio proceeded and reached 100% monomer conversion. The Mn and Mw/Mn of poly(MOVE-AdVE)(2:1) were 42,500 and 1.46, respectively. At the initial molar ratio of 3:1, the copolymerization also proceeded with approximately 100% monomer conversions and afforded the copolymer [poly(MOVE-AdVE)(3:1)] although the molecular weight distribution was broader (Mw/Mn ¼ 2.17) than those of the other copolymers. All the three copolymers exhibited unimodal MWDs. In DSC measurements of the copolymers, each polymer showed one glass transition temperature. The Tg’s of three copolymers obtained with the initial molar ratio of MOVE:AdVE ¼ 1:1, 2:1, and 3:1 were 59.9, 30.0, and 12.3  C, respectively. These results suggest that all the copolymerizations provided the copolymers with random monomer sequences. Fig. 1 shows 1H NMR spectra of the obtained poly(MOVE-AdVE)s in CDCl3 at room temperature. In all the spectra, the peaks around 3.5 ppm derived from oxyethylene units and the peaks around 1.5 ppm derived form adamantyl groups were observed, which confirms that all the polymers contain MOVE and AdVE units. Tables 2and 3 show the results of copolymerizations of MEEVE with AdVE and VEEM, respectively, under the same conditions as those of the copolymerization of MOVE with AdVE. Two copolymerizations of MEEVE with AdVE reached nearly 100% monomer conversions and gave the copolymers [poly(MEEVE-AdVE)(1:1) and poly(MEEVE-AdVE)(1.5:1)]. Poly(MEEVE-AdVE)s exhibited unimodal MWDs and unique Tg’s, indicating that they are random copolymers. Fig. 2(a) and (b) show 1H NMR spectra of poly(MEEVEAdVE)s. In both the spectra, the peaks derived from oxyethylene chains and the peaks derived from adamantyl groups were observed, which indicates that the copolymers were successfully formed by the copolymerization of MEEVE with AdVE. In the copolymerizations of MEEVE with VEEM, the monomer conversions did not reach 100% under the same reaction conditions as those of the copolymerizations with AdVE. The monomer conversions were in the range of 79e89% in all three copolymerizations. The copolymerizations provided the organic solvent-soluble polymers with relatively narrow MWDs, which suggests that only the vinyl ether group of the two vinyl groups in VEEM was selectively reacted. This is supported by 1H NMR spectra (Fig. 2(c) and (d)), that is the peaks derived from methacrylate group were clearly observed at 5.6 and 6.2 ppm. Table 1 Copolymerization of MOVE (M1) with AdVE (M2).a Feed ratio M1 : M2

[M1]0, M

[M2]0, M

Monomer conv., % M1 : M2

Mnb

Mw/Mnb

Tgc

1:1 2:1 3:1

0.60 0.80 0.90

0.60 0.40 0.30

100:100 100:100 98:97

40,000 42,500 25,100

1.67 1.46 2.17

59.9 30.0 12.3

a b c

In toluene at 0  C for 24 h, [IBEA] ¼ 1.0 mM, [Et1.5AlCl1.5] ¼ 20 mM. Measured by GPC with polystyrene calibration. Measured by DSC on second heating scan.

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T. Sakaguchi et al. / Polymer 53 (2012) 1659e1664 Table 3 Copolymerization of MEEVE (M1) with VEEM (M2).a Feed ratio M1:M2

[M1]0, M

[M2]0, M

Monomer conv., % M1:M2

Mnb

Mw/Mnb

Tg c

1:1 2:1 4:1

0.60 0.80 0.96

0.60 0.40 0.24

82:80 81:79 89:87

72,400 77,600 59,800

1.61 1.40 1.46

73 71 76

a b c

Fig. 1. 1H NMR spectra in CDCl3 of (a) poly(MOVE-AdVE)(1:1), (b) poly(MOVEAdVE)(2:1), and (c) poly(MOVE-AdVE)(3:1).

3.2. Solubility properties and preparation of polymer membranes The solubility of the obtained copolymers was showed in Table 4. The solubility was determined by the appearance of 1 wt% polymer solution after 24 h of mixing polymer into solvent. When a small amount of polymer could be observed, the solubility was determined as partially soluble. When a decrease of the added polymer could not be observed, the solubility was determined as insoluble. All the poly(MOVE-AdVE)s, poly(MEEVE-AdVE)s, and poly(MEEVE-VEEM)s totally dissolved in toluene, CHCl3, and THF, while they were partially soluble or insoluble in hexane, acetone, Table 2 Copolymerization of MEEVE (M1) with AdVE (M2).a Feed ratio M1:M2

[M1]0, M

[M2]0, M

Monomer conv., % M1:M2

Mnb

Mw/Mnb

Tgc

1:1 1.5:1

0.60 0.72

0.60 0.48

100:95 98:100

56,800 37,000

1.65 2.21

28.2 13.9

a b c

In toluene at 0  C for 24 h, [IBEA] ¼ 1.0 mM, [Et1.5AlCl1.5] ¼ 20 mM. Measured by GPC with polystyrene calibration. Measured by DSC on second heating scan.

In toluene at 0  C for 24 h, [IBEA] ¼ 1.0 mM, [Et1.5AlCl1.5] ¼ 20 mM. Measured by GPC with polystyrene calibration. Measured by DSC on second heating scan.

methanol, and H2O. The solubility in polar solvents such as acetone and methanol became better as decreasing the contents of AdVE in copolymers. The free-standing membranes of poly(MOVE-AdVE) and poly(MEEVE-AdVE) were prepared by solution casting method. The Tg’s of poly(MOVE-AdVE)(1:1), poly(MOVEAdVE)(2:1), and poly(MEEVE-AdVE)(1:1) were 59.9, 30.0, and 28.2, respectively, and their membranes could be obtained. However, the Tg’s of poly(MOVE-AdVE)(3:1) and poly(MEEVE-AdVE)(1.5:1) were 12.3 and 13.9, respectively, which were lower than room temperature. Therefore, these two copolymers could not form freestanding membranes. The membranes of poly(MEEVE-VEEM)s could be prepared by thermal crosslinking. Poly(MEEVE-VEEM)s were sticky liquid at room temperature because the Tg’s of poly(MEEVE-VEEM)(1:1), poly(MEEVE-VEEM)(2:1), and poly(MEEVE-VEEM)(4:1) were 73, 71 and 76  C, respectively. Heating the sticky liquid poly(MEEVE-VEEM)s placed in Petri dish afforded the free-standing membranes crosslinked by the reaction of methacrylate groups. Fig. 3 showed the IR spectra of poly(MEEVE-VEEM)s before and after heating. The absorptions at 1620 cm1 assigned to the stretching of C]C double bonds and at 1710 cm1 assigned to the stretching of C]O carbonyl bonds were observed in the spectra before heating (Fig. 3(a), (c), (e)). After heating at 60  C for 24 h, the peak intensity of the double bonds was decreased compared to the peak intensity of CeOeC stretching (1080 cm1). The conversion of C]C double bonds was calculated from the peak strength at 1620 cm1 on the basis of the peak at 1080 cm1 attributed to CeOeC stretching. The conversion of C]C double bonds for poly(MEEVE-VEEM)(1:1) was approximately 50%, while those for poly(MEEVE-VEEM)(2:1) and poly(MEEVE-VEEM)(4:1) were roughly 30%. Further, the peak around 1710 cm1 became broad and slightly shifted to high wavenumber. This may be due to the existence of non-conjugated carbonyl bonds as well as conjugated carbonyl bonds. These results also suggest that C]C double bonds of methacrylate groups partially reacted to form crosslinking. The membranes of poly(MEEVE-VEEM)s were insoluble in any solvents. 3.3. Gas permeability of the polymer membranes The permeability of their membranes to nitrogen, oxygen, and carbon dioxide was examined at 25  C. Gas permeability coefficients and separation factors of membranes of poly(MOVE-AdVE)s, poly(MEEVE-AdVE), and poly(MEEVE-VEEM)s are summarized in Table 5. The nitrogen permeability coefficients, P(N2), of membranes of poly(MOVE-AdVE)(1:1) and poly(MOVE-AdVE)(2:1) were 1.3 and 1.2 barrers, respectively. Their oxygen permeability coefficients, P(O2), were 3.9 and 3.8 barrers. The P(N2) and P(O2) values of membrane of poly(MOVE-AdVE)(1:1) are almost the same as those of poly(MOVE-AdVE)(2:1), respectively. On the other hand, the carbon dioxide permeability coefficient, P(CO2), of membrane of poly(MOVE-AdVE)(2:1) was 36 barrers, which is larger than that of poly(MOVE-AdVE)(1:1). Consequently, carbon dioxide separation factor, P(CO2)/P(N2), of membrane of poly(MOVE-AdVE)(2:1) was

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Table 4 Solubility of the polymers.a Hexane poly(MOVE-AdVE) (1:1)  (2:1)  (3:1)  poly(MEEVE-AdVE) (1:1)  (1.5:1)  poly(MEEVE-VEEM) (1:1) e (2:1) e (4:1) e poly(MEEVE-VEEM) (1:1) e (2:1) e (4:1) e a

Toluene

CHCl3

THF

Acetone

Methanol

H2O

þ þ þ

þ þ þ

þ þ þ

e þ þ

e e 

e e e

þ þ

e 

e e

e e

þ þ þ

þ þ þ

  þ

e e 

e e e

e e e

e e e

e e e

þ þ þ þ before crosslinking þ þ þ þ þ þ after crosslinking e e e e e e

Symbols þ: soluble, : partially soluble, e: insoluble.

Fig. 2. 1H NMR spectra in CDCl3 of (a) poly(MEEVE-AdVE)(1:1), (b) poly(MEEVEAdVE)(1.5:1), (c) poly(MEEVE-VEEM)(1:1), and (d) poly(MEEVE-VEEM)(4:1).

larger than that of poly(MOVE-AdVE)(1:1). Namely, the CO2 permselectivity increased as increasing the content of oxyethylene segment. This can be accounted for by the high affinity of oxyethylene segment to carbon dioxide. Polymer membranes containing polar groups such as oxyethylene segments exhibit very high CO2 solubility due to the interaction between CO2 and polar groups, while they do not particularly show high N2 solubility, and hence the membranes containing polar groups exhibit high CO2/N2 solubility selectivity [4]. In the present poly(vinyl ether)s, the CO2

Fig. 3. IR spectra of poly(MEEVE-VEEM)s before and after crosslinking.

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Table 5 Gas permeability coefficients (P)a of polymer membranes at 25  C.

poly(MOVE-AdVE)(1:1) poly(MOVE-AdVE)(2:1) poly(MEEVE-AdVE)(1:1) poly(MEEVE-VEEM)(1:1) poly(MEEVE-VEEM)(2:1) poly(MEEVE-VEEM)(4:1) a

P(N2)

P(O2)

P(CO2)

P(O2)/P(N2)

P(CO2)/P(N2)

1.3 1.2 0.55 0.10 0.81 2.1

3.9 3.8 2.1 0.45 3.5 8.5

25 36 22 3.70 46 120

3.0 3.2 3.8 4.5 4.3 4.0

19 30 40 37 57 57

In the unit of barrer (1 barrer ¼ 1  1010 cm3 (STP) cm/(s  cm2  cmHg).

solubility selectivity would increased as increasing the content of oxyethylene segment. Unfortunately, poly(MOVE-AdVE)(3:1) with the highest content of oxyethylene segment could not form a membrane because its Tg was lower than room temperature (12.3  C). The permeability coefficients to three gases of membrane of poly(MEEVE-AdVE) was smaller than those of poly(MOVE-AdVE) s, while the P(CO2)/P(N2) value was larger than those of poly(MOVE-AdVE)s. The membrane of poly(MEEVE-AdVE) with higher ratio of MEEVE could not be prepared because the copolymer had low Tg of 13.9  C. The crosslinked membrane of poly(MEEVE-VEEM)(1:1) showed the lowest gas permeability among all the membranes in the present study. Generally, a crosslinking restricts a motion of polymer chains, which leads the decrease of gas diffusion in the polymer matrix [6,30]. The gas permeability of membrane of poly(MEEVE-VEEM)(2:1) (P(CO2) ¼ 46 barrers) was much higher than that of poly(MEEVE-VEEM)(1:1). Moreover, the P(CO2)/P(N2) value of membrane of poly(MEEVE-VEEM)(2:1) was as large as 57. Membrane of poly(MEEVE-VEEM)(4:1) exhibited much higher gas permeability (P(CO2) ¼ 120 barrers) and maintained high CO2 permselectivity (P(CO2)/P(N2) ¼ 57). The high CO2 permeability and permselectivity of poly(MEEVE-VEEM)(4:1) may be due to a low number of crosslinking points and high content of oxyethylene segment. The relatively lack of crosslinking points would enhance gas diffusivity in polymer matrix, and the high content of oxyethylene segment would increase CO2 solubility selectivity. The feature of the present poly(vinyl ether) membranes is that they have short oxyethylene chains as side groups and they are wholly amorphous. Therefore, they exhibited high CO2 permeability. Especially, poly(MEEVE-VEEM)(4:1) showed the best separation performance in the present study, whose P(CO2) was one of the largest values among the CO2 separation membranes possessing high CO2 selectivity. For instance, the P(CO2) of semi-crystalline

PEO is 8.1 barrers at 25  C, which is smaller than poly(MEEVEVEEM)(4:1) by two orders of magnitude [5]. The crosslinked poly(ethylene glycol diacrylate) is amorphous, and its P(CO2) is as large as 145 barrers at 35  C [6]. Thus, membranes of poly(vinyl ether)s possessing oxyethylene segments as side chains showed high CO2 permeability, and the data of poly(MEEVE-VEEM)(4:1) was located near Robeson’s upper bound [31], as shown in Fig. 4. This implies that poly(MEEVE-VEEM)(4:1) has high CO2 permeability and high CO2 permselectivity, and hence poly(vinyl ether)s bearing oxyethylene segments are promising candidates of CO2 separation membranes. 4. Conclusions The present study demonstrates the synthesis of membranes of poly(vinyl ether)s bearing oxyethylene segments as side chains. The membranes of poly(MOVE-AdVE)s and poly(MEEVE-AdVE) exhibited relatively high CO2 permselectivity because of the high affinity of oxyethylene segments to CO2 molecules. The crosslinked membranes of poly(MEEVE-VEEM)s showed superior performance for CO2 separation, and poly(MEEVE-VEEM)(4:1), especially, exhibited high CO2 permeability and permselectivity because it possesses flexible polymer chain and high content of oxyethylene moiety. Acknowledgements We are grateful to Maruzen Petrochemical (Tokyo, Japan) for supplying MOVE and MEEVE monomers and to Nippon Shokubai for supplying VEEM monomer. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21] [22] [23] [24] [25] [26]

Fig. 4. Relationship between P(CO2)/P(N2) and P(CO2) for the present polymers.

[27] [28] [29] [30] [31]

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