Synthesis and oxygen permselectivity of copoly(substituted acetylene)s with bulky fused polycyclic aliphatic groups

Polymer 99 (2016) 695e703

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Synthesis and oxygen permselectivity of copoly(substituted acetylene) s with bulky fused polycyclic aliphatic groups Hongge Jia a, **, Jian Luo a, Toshiki Aoki a, b, *, Lijia Liu c, ***, Yu Zang a, Yinghui Lun b, Masahiro Teraguchi b, Takashi Kaneko b a

College of Materials Science and Engineering, Key Laboratory of Polymeric Composition and Modification, Qiqihar University, Wenhua Street 42, Qiqihar 161006, China Graduate School of Science and Technology, Niigata University, 2-8050 Ikarashi, Nishi-ku, Niigata 950-2181, Japan c Polymer Materials Research Center, Key Laboratory of Superlight Materials and Surface Technology, Ministry of Education, College of Materials Science and Chemical Engineering, Harbin Engineering University, Harbin 150001, China b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 14 April 2016 Received in revised form 14 June 2016 Accepted 7 July 2016 Available online 9 July 2016

We synthesized six phenylacetylenes (RCOPAs, RSOPAs, and RSPAs) having a bulky fused polycyclic aliphatic group, which is adamantyl(Ad), pinanyl(Pi), or cholesteryl(Ch) via oxycarbonyl (CO) or oxydimethylsilyl(SO), and the other two phenylacetylenes having less or non-bulky substituents, i.e., menthyloxycarbonylphenylacetylene (MtCOPA) or ethoxydimethylsilylphenylacetylene (EtSOPA) (Et ¼ Ethyl). The new monomers were polymerized and copolymerized with p-trimethylsilylphenylacetylene (SPA) by using catalyst [Rh(nbd)Cl]2 (nbd ¼ 2,5-norbornadiene) in trimethylamine to give soluble high molecular-weight polymers in relatively good yields. The resulting copolymers were fabricated to self-supporting membranes which had enough strength for separation membranes by solution casting method. As a result, we can discuss the relationship between bulky chemical structures and permeation behavior systematically for the first time. Oxygen permselectivities (PO2/PN2) of copolyRSOPAs having the bulky fused polycyclic aliphatic groups such as Ad and Pi were higher than those of copolyEtSOPAs. PO2/PN2 values of copolyRCOPAs were higher than those of polyRSOPAs when they had the same content of the identical bulky groups. The rigid spacer was effective for enhancing PO2/PN2. Among copolyRCOPAs with bulky fused polycyclic aliphatic groups, the copolymers with spherical substituents such as Pi and Ad groups showed higher PO2/PN2 values than those with a planer substituent i.e., Ch groups. PO2 values of copolyRSOPAs and copolyRCOPAs were 130e220 and 50e90 barrer, respectively. The flexible silyloxy spacers in RSOPAs were effective in enhancing their PO2 values. © 2016 Elsevier Ltd. All rights reserved.

Keywords: Copolyphenylacetylene Bulky fused polycyclic aliphatic groups Self-supporting membrane Spherical shape

1. Introduction Oxygen permselective membranes can separate oxygen from air just by permeation process with low energy. Therefore, it is energysaving process and very useful for our industrial society [1e3]. Although many inorganic membranes for oxygen selective

* Corresponding author. Graduate School of Science and Technology, Niigata University, 2-8050 Ikarashi, Nishi-ku, Niigata 950-2181, Japan. ** Corresponding author. College of Materials Science and Engineering, Qiqihar University, Wenhua Street 42, Qiqihar 161006, China. *** Corresponding author. Polymer Materials Research Center, Harbin Engineering University, Harbin 150001, China. E-mail addresses: [email protected] (T. Aoki), [email protected] (L. Liu). http://dx.doi.org/10.1016/j.polymer.2016.07.023 0032-3861/© 2016 Elsevier Ltd. All rights reserved.

permeation such as carbonized membranes [4,5] or molecularsieving membranes [6] have been recently reported, polymeric membranes including polymer intrinsic microporosity(PIM) [7,8] are still very attractive and have many advantages because they have good membrane forming ability and therefore their thin membrane can be easily prepared. In addition, since the molecular structures of organic polymers can be designed precisely and freely, realization of permselective membranes having higher performances are expected. Membranes from polymers such as polysulfone, cellulose, polydimethylsiloxane, polyimide, polyamide, PIM [7,8], and poly(substituted acetylene)s [9,10] were reported as oxygen permselective membranes. Among them, poly(substituted acetylene)s are known not only as good oxygen permselective membrane materials, but also as interesting p-conjugated materials

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concerning electric conductivity, photoemissions, and magnetism. Therefore, synthesis and characterization of many kinds of the polymers have been reported. Masuda [11,12] have studied synthesis and oxygen permeation of polymers of mono- and disubstituted acetylenes bearing many kinds of substituents by using metathesis catalysts. Since the catalysts gave very high molecular weight polymers even if the monomer has bulky substituents, it was very useful for obtaining good oxygen permselective membrane materials. For example, poly(1-trimethylsilyl-1-propyne) have the highest oxygen permeability coefficient so far. However, it was difficult to obtain soluble and high-molecularweight poly(substituted acetylene)s having polar functional groups such as oxygen-containing groups by the metathesis catalysts and in addition even if such polymers were successfully obtained, their self-standing membrane forming abilities were not always good because of their low solubilities [13]. Therefore, systematic study on the relationships between chemical(primary) structures and permselectivities was not enough, although it is the most important aspect. On the other hand, Rh catalysts such as [Rh(nbd)Cl]2 (nbd ¼ 2,5-norbornadiene) can always produce soluble and very high molecular weight polymers having many kinds of polar groups and bulky substituents. Therefore, it made possible the study, i.e., to discuss the relationship between chemical(primary) structures and permeation behavior systematically. Some of the authors have synthesized various phenylacetylene monomers in order to obtain oxygen permeation membranes during the past three decades [9,10,14e25]. Most of these polymeric membranes reported had relatively small and non-polar substituents having flexibility or high mobility such as oligosiloxanyl groups because the aim was to obtain membranes having high oxygen permeability(PO2), not high oxygen permselectivity(a ¼ PO2/PN2). In other words, to enhance their PO2 values, introduction of small and non-polar substituents with flexibility or high mobility was effective because they can enlarge spaces between macromolecules. However, it is not clear how to enhance permselectivitiy (PO2/PN2). In order to enhance PO2/PN2, the size and distribution of molecular-size spaces between macromolecules should be controlled. However no strategies for such controls have not been reported. Here in order to find a guide for obtaining polymer membranes with higher permselectivity, we studied the relationship between chemical structures and permeation behavior systemically. First we synthesized and (co)polymerized novel phenylacetylenes (RCOPAs and RSOPAs) (Chart 1) having a bulky fused polycyclic aliphatic group connected by different spacers (CO and SO), and then measured their oxygen permeation behavior, and finally discussed the effect of the shape of the substituents on permselectivity. 2. Experimental 2.1. Materials All the solvents used for synthesis and polymerizations of the monomers were distilled as usual. The polymerization initiator, [Rh(nbd)Cl]2 (nbd ¼ 2,5-norbornadiene), purchased from Aldrich Chemical Co., Inc., was used as received. According to our previous papers, SPA [22], PiSPA [25], PiCOPA [26] and MtCOPA [27] were prepared. Other materials purchased from Tokyo Chemical Co., Ltd., were used as received. 2.2. Synthesis of monomers (RCOPAs, RSOPAs, and RSPAs) 2.2.1. Synthetic procedures and characterizations of the monomers RCOPAs (AdCOPA and ChCOPA) (Scheme 1) All the following reaction procedures were conducted under dry

nitrogen. 2.2.1.1. Admantyl p-bromobenzoate (1a). Thionyl chloride (60 ml) was added to p-bromobenzoic acid (5.56 g, 27.7 mmol) and the solution was refluxed for 6 h. After the residual thionyl chloride was removed from the solution, a white needle crystal formed. A solution of admantanol (5.10 g, 33.5 mmol) in toluene (60 ml) was added to the reaction mixture and the solution was refluxed for 24 h. After the toluene was removed, a yellow solid was obtained. The crude product was purified by silica-gel column chromatography to give 1a as a white solid. Yield: 46.0% (4.47 g). Rf ¼ 0.85 (chloroform). 1H NMR (CDCl3, TMS): d 7.86 and 7.53 (2d, 4H, phenyl), 2.26 and 1.73 (2b, 15H, admantyl). 2.2.1.2. Cholesteryl p-bromobenzoate (1b). A similar procedure to that for synthesis of 1a described above was used. Appearance: a white solid. Yield: 87.6%. Rf ¼ 0.8 (chloroform). 1H NMR (CDCl3, TMS): d 7.92 and 7.55 (2d, 4H, phenyl), 2.60e0.68 (m, 45H, cholesteryl). 2.2.1.3. 4-[p-(Admantyloxycarbonyl)phenyl]-2-methyl-3-butyn-2-ol (2a). 2-Methyl-3-butyn-2-ol (0.11 ml, 1.50 mmol) was added to a solution of PdCl2(Ph3P)2 (10.54 mg, 0.015 mmol), Ph3P (7.88 mg, 0.03 mmol), CuI (5.74 mg, 0.03 mmol) and 1a (0.33 g, 0.97 mmol) in dry triethylamine (10 ml). The mixture was refluxed for 6 h. After the mixture was filtered, the solvent was removed. The crude product was purified by silica-gel column chromatography to give 2a as a yellow liquid. Yield: 84.9% (0.13 g). Rf ¼ 0.2 (chloroform). 1H NMR (CDCl3, TMS): d 7.89 and 7.39 (2d, 4H, phenyl), 2.62 (b, 1H, OH), 2.22 and 1.70 (2b, 15H, admantyl), 1.56 (s, 6H, C(CH3)2). 2.2.1.4. 4-[p-(Cholesteryloxycarbonyl)phenyl]-2-methyl-3-butyn-2ol (2b). A similar procedure to that for synthesis of 2a described above was used. Appearance: yellow liquid, Yield 78.5%. Rf ¼ 0.2 (chloroform). 1H NMR (CDCl3, TMS): d 7.94 and 7.40 (2d, 4H, phenyl), 2.71 (b, 1H, OH), 2.50e0.67 (m, 45H, cholesteryl), 1.59 (s, 6H, C(CH3)2). 2.2.1.5. p-(Admantyloxycarbonyl)phenylacetylene (AdCOPA). A solution of 2a (0.13 g, 0.38 mmol) in toluene (70 ml) was added to sodium hydride (9.12 mg, 0.38 mmol). After the mixture was stirred at 90  C for 1 h, the mixture was filtered. The crude product was purified by silica-gel column chromatography to give AdCOPA as a yellow solid. Yield: 64.0% (2.44 g). Rf ¼ 0.80 (chloroform). 1H NMR (CDCl3, TMS): d 7.94 and 7.52 (2d, 4H, phenyl), 3.22 (s, 1H. HC^C), 2.25 and 1.72 (m, 15H, admantyl). 2.2.1.6. p-(Cholesteryloxycarbonyl)phenylacetylene (ChCOPA). A similar procedure to that for synthesis of AdCOPA described above was used. Appearance: a yellow solid, Yield 55.3%. Rf ¼ 0.8 (chloroform). 1H NMR (CDCl3, TMS): d 8.02 and 7.53 (2d, 4H, phenyl), 3.22 (s, 1H, HC^C), 2.63e0.70 (m, 45H, cholesteryl). 2.2.2. Synthetic procedures and characterizations of the monomers RSOPAs (PiSOPA, AdSOPA, and EtSOPA) (Scheme 2) 2.2.2.1. 1-Bromo-4-(chlorodimethylsilyl)benzene (3). A solution of n-butyllithium in hexane (75.3 ml, 120 mmol) was added dropwise to a solution of p-dibromobenzene (28.4 g, 120 mmol) in dry ether (100 ml). After it was stirred for 2 h at 0  C, the solution of the monolithiated compound was added dropwise to dichlorodimethylsilane (29.2 ml, 240 mmol). The reaction mixture was stirred for 6 h at room temperature. After the formed salt was filtered off, the solvent was removed by evaporation. The crude product was purified by vacuum distillation to give 3 as a clear liquid. Yield: 49.1% (14.8 g). bp: 66e72  C (0.10 mmHg). 1H NMR

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Scheme 1. Synthetic route of monomers with a bulky fused polycyclic aliphatic group via an ester spacer (RCOPAs, AdCOPA and ChCOPA).

Scheme 2. Synthetic route of monomers with a bulky fused polycyclic aliphatic group via a siloxyspacer (RCOPA; PiSOPA and AdSOPA). (Note) In all the codes used in this article, S indicates silicon.

(CDCl3, TMS): d 7.58 and 7.50 (2d, 4H, phenyl), 0.69 (s, 6H, Si(CH3)2).

2.2.2.4. 1-Bromo-4-adamantyloxydimethylsilylbenzene (4b). A similar procedure to that for 1-bromo-4ethyloxydimethylsilylbenzene described above was used. The crude product was purified by silica-gel column chromatography to give 4b as a white solid. Yield: 91.5%. Rf ¼ 0.95 (ethyl acetate).

2.2.2.2. 1-Bromo-4-ethyloxydimethylsilylbenzene (R ¼ ethyl in Scheme 2). To a solution of triethylamine (40 ml) and ethanol (10 ml), 3 (14.80 g, 59.20 mmol) was added dropwise. It was stirred for 6 h at room temperature. After the formed salt was filtered off, the solvent was removed by evaporation. The crude product was purified by vacuum distillation to give clear liquid (4e). Yield: 80.2% (12.3 g). bp: 65e79  C (0.12 mmHg). 1H NMR (CDCl3, TMS): d 7.53 and 7.44 (2d, 4H, phenyl), 3.66 (q, 2H, OCH2CH3), 1.19 (t, 3H, OCH2CH3), 0.37 (s, 6H, Si(CH3)2).

2.2.2.5. 4-[p-(Pinanyloxydimethylsilyl)phenyl]-2-methyl-3-butyn-2ol (5a). A similar procedure to that for synthesis of 2 described above was used. The crude product was purified by silica-gel column chromatography to give 5b as a clear liquid. Yield: 84.1%. Rf ¼ 0.5 (ethyl acetate/hexane ¼ 1/3(v/v)).

2.2.2.3. 1-Bromo-4-pinanyloxydimethylsilylbenzene (4a). A similar procedure to that for 1-bromo-4-ethyloxydimethylsilylbenzene described above was used. The crude product was purified by silica-gel column chromatography to give 4a as a clear liquid. Yield: 94.4%. Rf ¼ 0.7 (ethyl acetate/hexane ¼ 1/4(v/v)).

2.2.2.6. 4-[p-(Adamantyloxydimethylsilyl)phenyl]-2-methyl-3butyn-2-ol (5b). A similar procedure to that for synthesis of 2 described above was used. The crude product was purified by silicagel column chromatography to give 5c as a yellow liquid. Yield: 69.9%. Rf ¼ 0.5 (ethyl acetate/hexane ¼ 1/3(v/v)).

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2.2.2.7. p-(Pinanyloxydimethylsilyl)phenylacetylene (PiSOPA). A similar procedure to that for synthesis of AdCOPA was used. The crude product was purified by silica-gel column chromatography to give PiSOPA as a yellow liquid. Yield: 42.0%. Rf ¼ 0.8 (ethyl acetate/ hexane ¼ 1/3(v/v)). 1H NMR (CDCl3, TMS): d 7.58 and 7.48 (2d, 4H, phenyl), 3.11 (s, 1H, HC^C), 2.40e0.85 (m, 16H, pinanyl), 0.39 (s, 6H, Si(CH3)2). 2.2.2.8. p-(Adamantyloxydimethylsilyl)phenylacetylene (AdSOPA). A similar procedure to that for synthesis of AdCOPA was used. The crude product was purified by silica-gel column chromatography to give AdSOPA as a yellow liquid. Yield: 46.3%. Rf ¼ 0.8 (ethyl acetate/ hexane ¼ 1/3(v/v)). 1H NMR (CDCl3, TMS): d 7.53 and 7.44 (2d, 4H, phenyl), 3.12 (s, 1H, HC^C), 2.08e1.57 (m, 15H, admantyl), 0.39 (s, 6H, Si(CH3)2). 2.2.2.9. p-(Ethyloxydimethylsilyl)phenylacetylene (EtSOPA). A similar procedure to that for synthesis of AdCOPA was used. The crude product was purified by vacuum distillation to give clear liquid EtSOPA. Yield: 92.0%. Bp: 60e65  C (0.10 mmHg). 1H NMR (CDCl3, TMS): d 7.54 and 7.46 (2d, 4H, phenyl), 3.66 (q, 2H, OCH2CH3), 3.12 (s, 1H, HC^C), 1.18 (t, 3H, OCH2CH3), 0.39 (s, 6H, Si(CH3)2). 2.3. Polymerizations 2.3.1. Homopolymerizations of the monomers (PAs) A typical polymerization procedure was exampled by ChCOPA as follows: A solution of [Rh(nbd)Cl]2 (0.72 mg, 1.56 mmol) in trimethylamine(TEA) (0.20 ml) was added to a solution of a monomer ChCOPA (103 mg, 200 mmol) in THF (0.20 ml). The reaction solution was stirred at room temperature for 4 h. The formed polymer was purified by precipitation of the polymerization solution into a large amount of methanol, and dried in vacuum to give a polyChCOPA. Yield: 56.3% (72.1 mg). GPC: Mw ¼ 1.19  106. Mw/Mn ¼ 3.1 (Table 1, no. 6). 1H NMR (CDCl3, TMS): d 7.70 (b, 4H, phenyl), 6.65, 5.78, 5.42 and 4.74 (4b, 1H, HC]C), 2.40 and 0.70 (b, 45H, cholesteryl). The other polymerizations of the other monomers were also

conducted similarly. The results are listed in Table 1, Nos. 1, 4, 6, 10,12, and 14. 2.3.2. Copolymerizations of the monomers (PAs) with SPA A typical copolymerization procedure was exampled by ChCOPA as follows (The feed of ChCOPA was 12.9 mol%.): After the copolymerization whose condition was similar to that for homopolymerizations, the formed copolymer was purified by precipitation of the THF solution into a large amount of methanol, and dried in vacuum to give a red copolyChCOPA. Yield: 78.7%. GPC: Mw ¼ 8.3  105. Mw/Mn ¼ 2.3. 1H NMR (CDCl3, TMS): d 7.68 and 7.15 (2b, 4H, phenyl), 6.52, 5.85 and 5.44 (3b, 1H, HC]C), 2.43 and 0.70 (b, 6H, cholesteryl), 0.12 (b, 8H, Si(CH3)3). Composition of ChCOPA unit in copolyChCOPA was 12.9 mol% (by NMR). The other copolymerizations of the other monomers with SPA were also conducted similarly. The results are listed in Table 1, Nos. 2, 3, 5, 7e9,11,13, and 15e18. 2.4. Membrane preparation A typical membrane fabrication method was as follows: A solution of a polymer (10.0 wt%) in chloroform or THF (40 ml) was cast on a poly(tetrafluoroethylene) sheet (4 cm2). (Note: Only membranes of PolyPiSOPA were prepared by solvent casting of the polymerization solution directly without purification by precipitation to avoid gelation.) After evaporating of the solvent for 12 h at room temperature, the membranes were detached from the sheet and dried in vacuo for 24 h. Thicknesses (L) of the membranes were 50.0e80.0 mm. 2.5. Measurements Oxygen and nitrogen permeability coefficients (PO2 and PN2: barrer ¼ 1010 cm3(STP) cm cm2 s1 cmHg1) and the oxygen separation factor (a ¼ PO2/PN2) were measured with 1 atm pressure difference at 25  C by a gas chromatographic method by using YANACO GTR-10 according to our previous report [21]. The diffusion coefficient (D: cm2 s1) was calculated from D ¼ L2/6q, where

Table 1 Copolymerizations of RCOPAs or RSOPAs with SPA by using [Rh(nbd)Cl]2/TEA.a No.

Monomer

Feed of monomer (mol%)

Composition of monomer unit in copolymer (mol%)b

Yield (%)

Mwc (105)

Mnc (105)

Membrane formationd

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

AdCOPA

100 50 20 100 40 100 25 10 5 100 20 100 20 100 70 46 20 9

100.0 48.3 23.0 100.0 43.1 100.0 24.4 12.9 6.2 100.0 25.4 100.0 12.6 100.0 75.6 53.1 21.6 12.0

87.9 91.7 91.2 47.9 77.0 56.3 72.7 78.7 78.8 20.2 72.4 15.5 80.0 Gel 72.1 68.5 59.3 62.7

10.4 9.7 13.5 5.7 9.3 11.9 39.5 8.3 12.9 0.2 5.2 2.4 16.8

3.2 3.6 2.7 4.0 3.1 3.1 3.5 2.3 3.6 2.9 1.5 6.3 2.0

13.2 12.4 16.0 8.3

3.2 3.0 2.1 2.7

þ þþ þþ þ þþ þ þ þ þþ þ þþ  þþ e þþ þþ þþ þþ

PiCOPA ChCOPA

EtSOPA AdSOPA PiSOPA

a At room temperature in THF and TEA, TEA/THF ¼ 1/1(v/v), [RCOPAs þ SPA] ¼ 0.2 mol/L, [RSOPAs þ SPA] ¼ 0.1 mol/L, [RCOPAs þ SPA]/[Catalyst] ¼ 1000, [RSOPAs þ SPA]/ [Catalyst] ¼ 300. b Determined by 1H NMR. c Determined by GPC correlating polystyrene standard with THF eluent. d þþ: Excellent, þ: Good, : poor. e The polymerization system of homogeneous during polymerization but after precipitation, the product became insoluble.

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L(cm) is the thickness of the membrane and q(s) is the time-lag. 1H NMR (60 MHz) spectra were recorded on a JMN-PMX60 spectrometer. The average molecular weights (Mn and Mw) were evaluated with THF eluent (1.0 ml/min) at room temperature by gel permeation chromatography (GPC) by using JASCO(655A-11) liquid chromatograph instruments with GL-F100M(8 mm  50 mm), GLF100C(4 mm  10 mm).

Mw. Therefore, we could obtain these high Mw homopolymers successfully by the same conditions. Compared with RSOPAs having an unstable siloxy spacer, RCOPAs gave the corresponding homopolymers in higher yields (47.9e87.9%). The SiOC bonds in RSOPAs tend to be partly hydrolyzed to yield SiOH which can give bad effect on the polymerization. Therefore, the higher yield may be caused by their more stable ester groups than siloxy group.

3. Results and discussion

3.1.3. Copolymerization of phenylacetylenes (RCOPAs and RSOPAs) having a bulky fused polycyclic aliphatic group with ptrimethylsilylphenylacetylene (SPA) The copolymerizations of phenylacetylenes (RCOPAs or RSOPAs) with p-trimethylsilylphenylacetylene (SPA) were carried out by using [Rh(nbd)Cl]2/TEA catalytic system (Table 1). The compositions of RCOPAs or RSOPAs unit in the copolymers were determined by 1H NMR. The compositions were found to be similar to the feed ratio of the monomer and comonomer. Therefore, in spite of their high bulkiness of the fused polycyclic aliphatic group, their polymerization reactivities were found to be similar to that of SPA with a much smaller substituent(trimethylsilyl). Although homopolymerization of PiSOPA did not yield soluble polymers, copolymerizations of PiSOPA with SPA gave the corresponding copolymer with 8.0e16.0  105 of Mw in 59.3e72.1% yields (Table 1, nos. 15e18). In addition, the yields and Mw of copolyEtSOPA and copolyAdSOPA were 72.4%, 80.0% and 5.2  105, 1.68  106, respectively (Table 1, nos 11 and 13). The values were higher than those of homopolymerizations and homopolymers of EtSOPA and AdSOPA (Table 1, nos 10 and 12). Similarly in the case of the copolymerizations of RCOPAs with SPA, higher yields and Mw were observed than those of homopolymerizations and homopolymers. Because of their high bulkiness in, the homopolymerization did not give polymers with high yield and Mw, while SPA having a compact substituent was reported to have very good polymerization ability [21]. Therefore copolymers of RCOPAs or PSOPAs with SPA having higher yields and Mw could be obtained.

3.1. Synthesis and membrane preparation of polyphenylacetylenes (polyRCOPAs, polyRSOPAs) having bulky fused polycyclic aliphatic groups 3.1.1. Synthesis of phenylacetylenes (RCOPAs and RSOPAs) having a bulky fused polycyclic aliphatic group According to Scheme 1, the phenylacetylenes (RCOPAs) having a bulky fused polycyclic aliphatic group via an ester group were synthesized from p-bromobenzoic acid by three-step reaction. The acids were easily converted to the corresponding eaters(1a and 1b) by esterification reaction via the acid chloride. The cross-coupling of 2-methyl-3-butyn-2-ol and the bromobenzoates with a palladium catalyst followed by removal of the protecting group was a convenient method to prepare these phenylacetylenes having the bulky substituent. These structures of the obtained monomers were confirmed by lH NMR where all the peaks were assigned. In the synthetic procedure of RSOPAs having a bulky fused polycyclic aliphatic group via a siloxy group (Scheme 2), first 1bromo-4-(chlorodimethylsilyl)benzene (3) was obtained from pdibromobenzene by using n-butyllithium and dichlorodimethylsilane in 49.1% yield. Secondly, the bulky fused polycyclic aliphatic groups (4a and 4b) were introduced by the condensation reaction of 3 and the corresponding alcohols in high yields (80.2e94.4%). Finally the monomers PiSOPA and AdSOPA were prepared from the precursors (5a and 5b) according to the same methods for RCOPAs. The chemical structures were confirmed by lH NMR. In spite of their high bulkiness of the substituents, these monomers were successfully synthesized in high yields. 3.1.2. Homopolymerizations of phenylacetylenes (RCOPAs and RSOPAs) having a bulky fused polycyclic aliphatic groups The novel monomers having bulky groups together with the other related monomers (Chart 1) were polymerized by using [Rh(nbd)Cl]2/trimethylamine(TEA) catalytic system, and the results of homopolymerization are summarized in Table 1, nos.1, 4, 6, 10, 12, and 14. AdCOPA containing a bulky adamantyl group via ester spacer was polymerized by using the catalytic system to give the corresponding homopolymers in 87.9% yield with 1.04  106 of Mw (Table 1, no. 1). Polymerizations of PiCOPA and ChCOPA gave the corresponding homopolymers in moderate yields(47.9 and 56.3%) with high Mw (5.7  105 and 1.19  106, respectively) (Table 1, nos. 4 and 6). Monomers EtSOPA and AdSOPA having an ethyl group and a bulky admantyl group via a siloxy spacer were polymerized to give the corresponding homopolymers in 20.2% and 15.5% yields with 2  104 and 2.4  105 of Mw, respectively (Table 1, nos. 10 and 12). The polymerization of PiSOPA containing a pinanyl group gave an insoluble polymer (No.14) (Note: The polymerization system of homogeneous during polymerization but after precipitation, the product became insoluble.) Although the size of the substituents(R) in RCOPAs and RSOPAs are very different (the decreasing order is Ch [ Pi > Ad [ Et), there are no relations between the bulkiness and the yields and

3.1.4. Membrane preparation of polyphenylacetylenes (copolyRCOPAs and copolyRSOPAs) having bulky fused polycyclic aliphatic groups Although the homopolymers of AdSOPA or PiSOPA did not form a self-supporting membrane by solution casting method (- in Table 1, nos. 12 and 14), copolyAdSOPA and copolyPiSOPA could be easily fabricated into self-supporting membranes which were tough enough to be applied as oxygen permselective membranes (þþ in Table 1, nos. 13, 15e18). Since the other homopolymers also showed low self-supporting property (þ in Table 1), they also were copolymerized with SPA. The resulting copolymers showed good membrane forming ability(þþ in Table 1, nos. 2,3,9 and 11). SPA can enhance their membrane forming ability significantly. 3.2. Relationship between chemical structures of the (co)polymers and their oxygen permselectivity 3.2.1. Effects of chemical structures of the substituents(R) in the copolymers on their oxygen permselectivities As described above, since we synthesized and copolymerized several (co)polymers who have the same content of different substituents(R) and the same main chains, and obtained their selfstanding membranes which had enough strength as separation membranes in spite of very bulky substituents, we can compare and discuss the effect of the substituents(R) on the permselectivities first. In order to compare and discuss the effects of chemical structures of the substituents (R) in the copolymers on their oxygen permselectivity, we measured oxygen and nitrogen permeability

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(PO2 and PN2) through the copolymers of RSOPAs or RCOPAs with p-trimethylsilylphenylacetylene(SPA) having different bulkiness and the same composition. The results are listed in Table 2. Fig. 1 shows the plots of oxygen separation factors (a ¼ PO2/PN2) versus oxygen permeability coefficients (PO2: barrer) through copolyRSOPA having different bulkiness and the same composition of the substituents and Fig. 2 shows the plots of a versus PO2 through copolyRCOPA having different bulkiness and the same composition of the substituents. As shown in Fig. 1, among the copolyRSOPAs having the same spacer, siloxy groups(SO), copolyPiSOPA and copolyAdSOPA having bulky groups showed higher a than copolyEtSOPA having non-bulky groups with keeping similar PO2 values. Therefore, bulky groups such as Pi and Ad were effective for obtaining good oxygen permselectivities. However, copolyPiCOPA and copolyAdCOPA showed higher a than copolyChCOPA and copolyMtCOPA among the copolyRCOPAs having the same spacers, i.e., ester groups(CO), although they all have bulky groups(Fig. 2). The decreasing order of their oxygen permselectivity coefficients was: copoly PiCOPA > copolyAdCOPA [ copolyChCOPA ¼ copolyMtCOPA as shown in Fig. 2. Although the three very bulky groups, i.e., Pi, Ad, and Ch are a fused polycyclic aliphatic group, Pi and Ad have a spherical shape and Ch has a planar shape (Chart 2). Judging from the shape of these bulky substituents, spherical groups such as Pi and Ad were more effective for enhancing a values with marinating PO2 values. In spite of its very bulky substituents, the effect of Ch on enhancing a values was low and similar to that of Mt whose bulkiness is much smaller than Ch. In other words, it was found the large planar structure such as Ch has a very low effect which is similar to much smaller Mt. In conclusion, introduction of bulky fused polycyclic aliphatic groups with spherical shapes (Pi and Ad) was suitable for better oxygen permselective membrane materials to poly(substituted acetylene)s. 3.2.2. Effects of chemical structures of the spacer (CO or SO) in the (co)polymers on their oxygen permselectivity Fig. 3 shows plots of oxygen separation factors (a ¼ PO2/PN2) versus oxygen permeability coefficients(PO2: barrer) through the homopolymers containing the same bulky substituents(Pi) and three different spacers(CO, SO, or S) having different flexibility(Chart 3). Fig. 4 shows plots of a versus PO2 through the copolymers with similar composition of bulky substituents (Pi or Ad) and two different spacers(CO or SO) having different flexibility. As shown in Fig. 3 and Table 3, the most compact and rigid spacer, ie., ester group (CO) was found to be better for good permselectivities than flexible siloxy spacer (SO). Fig. 5 also shows the spacer CO was always better for good permselectivities than SO between polymers having the same substituents (For example, PolyPiCOPA [ PolyPiSOPA, CopolyPiCOPA > CopolyPiSOPA, CopolyAdCOPA > CopolyAdSOPA). It may be caused by the rigid

3.3

CopolyPiSOPA

3.25

CopolyAdSOPA α 3.2

3.15 CopolyEtSOPA

3.1

1

100 PO2(barrer)

10000

Fig. 1. Oxygen permselectivities of copolyRSOPAs having bulky fused polycylic aliphatic groups(Pi and Ad) together with a non-bulky group(Et) (Table 2).

3.6 3.5

CopolyPiCOPA

3.4 CopolyAdCOPA α 3.3 3.2 CopolyMtCOPA

3.1

CopolyChCOPA 3

1

100 PO2 (barrer)

10000

Fig. 2. Oxygen permselectivitys of copolyRCOPAs having bulky fused polycylic aliphatic groups(Pi, Ad, and Ch) together with a less bulky group(Mt) (Table 2).

nature of CO. Unexpectedly, in the case of polyPiSPA having rigid or less flexible silyl spacers, a was the lowest (Fig. 3). Although the reason is not clear, because the mobility of the bulky groups connected by SieC bonds directly in poly(PiSPA) must be lower than

Table 2 Oxygen permselectivity of membranes from copolyRCOPAs or copolyRSOPAs having bulky fused polycyclic aliphatic groups and other less bulky groups. No.

Copolymer

Monomer unit content (wt%)

PO2a (barrer)

PO2/PN2

DO2b (106)

DO2/DN2

SO2c (103)

SO2/SN2

1 2 3 4 5 6 7

CopolyMtCOPA CopolyPiCOPA CopolyAdCOPA CopolyChCOPA CopolyEtSOPA CopolyPiSOPA CopolyAdSOPA

32.0 32.0 32.5 32.4 18.0 32.0 32.0

62.40 53.10 92.00 64.00 221.00 131.00 182.00

3.07 3.49 3.36 3.05 3.13 3.26 3.22

e 2.60 0.90 0.50 e 3.26 e

e 2.40 2.00 1.80 e 2.66 e

e 2.00 10.40 13.10 e 4.00 e

e 1.47 1.66 1.73 e 1.23 e

a b c

Barrer ¼ 1010cm3(STP)$cm$cm2$s1$cmHg1. In cm2$sec1. In cm3(STP) cm3$cmHg1.

H. Jia et al. / Polymer 99 (2016) 695e703

4.7

4.5

4.5

4.3

4.3

PolyPiSOPA

4.1

α 3.9 3.7

3.7

3.5

3.5 PolyPiSPA

3.1

1

100 PO2 (barrer)

10000

Fig. 3. Oxygen permselectivities of homopolymers of Pi containing PA monomers having different spacers (CO, SO and S) (Table 3) (Note: Only membranes of PolyPiSOPA were prepared by solvent casting of polymerization solution directly without purification by precipitation to avoid gelation.).

3.5

CopolyPiCOPA

3.4

CopolyAdCOPA

3.3

CopolyPiSOPA

α

3.2

3.1

CopolyAdSOPA

1

CopolyMtCOPA CopolyChCOPA 1

CopolyPiSOPA CopolyAdSOPA CopolyEtSOPA

100 PO2 (barrer)

10000

Fig. 5. Oxygen permselectivity behavior of copolyRCOPAs and copolyRSOPAs having different substituents.

copolymers with Pi were always better than those with Ad (Fig. 4) (For example, PolyPiCOPA > PolyAdCOPA, CopolyPiSOPA > CopolyAdSOPA). PO2 of copolyRSOPAs and copolyRCOPAs were 130e220 and 50e90 barrer, respectively (Table 2). The flexible silyloxy spacers in RSOPAs were effective in enhancing their PO2.

3.6

100 PO2 (barrer)

10000

Fig. 4. Oxygen permselectivities of copolymers having spherical bulky fused polycylic aliphatic groups (Pi and Ad) (Table 2).

Table 3 Oxygen permselectivity of membranes from homopolyphenylacetylenes (polyPiCOPA, polyPiSOPA and polyPiSPA). No.

Polymer

PO2a (barrer)

PO2/PN2

DO2b (106)

DO2/DN2

SO2c (103)

SO2/SN2

1 2 3 4

PolyPiCOPA PolyPiSOPA PolyPiSPA PolySPA

7.10 10.30 6.27 171.00

4.72 4.22 3.30 2.70

0.87 0.30 0.84 2.26

2.57 1.21 1.40 1.34

0.82 3.43 0.75 7.60

1.84 3.47 2.36 2.01

c

PolyPiSPA

3.1

2.9

CopolyAdCOPA

CopolyPiCOPA

3.3

3.3

a

PolyPiSOPA

4.1

α 3.9

b

PolyPiCOPA

4.7

PolyPiCOPA

701

Barrer ¼ 1010 cm3(STP) cm$cm2s1cmHg1. In cm2$sec1. In cc(STP)$cm3$cmHg1.

those of poly(PiSOPA) via eOe bonds between Si atoms and the bulky Pi groups, its membrane tends to have defects because of the rigid spacer. When we compared copolymers with Pi and Ad,

3.2.3. Relationship between chemical structures of the (co)polymers and their oxygen permselectivities Fig. 5 summarizes all the oxygen permselective behaviors measured in this study. In general, the polymers and copolymers with Pi groups or/and CO spacers had relatively good performances. In particular, the homopolymer and copolymer of PiCOPA having a pinanyl group and an ester spacer with p-trimethylsilylphenylacetylene(SPA) showed good performances. The homopolymer of PiCOPA showed the highest oxygen permselectivity (a ¼ PO2/PN2 ¼ 4.72) among all the results in this study. The copolymer of PiCOPA also the highest a (¼3.49) among the copolymers in this study which was 1.3 times higher than poly(SPA) (a ¼ 2.7). Therefore, Pi is the best substituent for obtaining good performance in this study. 3.2.4. Reason for the good effect of spherical substituents (Pi and Ad) on the oxygen permselectivity As described in 3.2.1, spherical substituents (Pi and Ad) had good effects on the oxygen permselectivity. To discuss the reason for the good effect of spherical substituents (Pi and Ad), their diffusion selectivities (¼ DO2/DN2) were calculated from the time lags. They are listed in Tables 2 and 3 They indicate that the higher a (¼ PO2/PN2) values of the copolymers and homopolymers having Pi or Ad were mainly caused by their higher DO2/DN2. Their good performances are ascribed to their good diffusion selectivities. In general small gas molecules such as oxygen and nitrogen can permeate molecular-sized spaces between macromolecules in dense membranes like polymer membranes used in this study. Therefore, to enhance permeation selectivity largely and effectively based on diffusion selectivity, the size and size distribution of the molecular-sized spaces must be controlled. Although the control is difficult because the spaces are dynamic, in order to form such regular molecular-sized spaces, it may be better to use symmetrical substituents such as spherical ones. Therefore, we think the

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H. Jia et al. / Polymer 99 (2016) 695e703

Chart 1. Chemical structures of the monomers having a bulky fused polycyclic aliphatic substituent via different spacers together with the other monomers having a less or nonbulky group in this study (RCOPAs, RSOPAs and RSPAs).

Chart 2. Chemical structures of the bulky substituents(R) in RCOPAs or RSOPAs having bulky fused polycyclic aliphatic groups (Pi, Ad, and Ch) and a bulky group (Mt).

copolymers and homopolymers having Pi or Ad showed good oxygen selective permeation based on diffusion selectivity.

Chart 3. Chemical structures of the spacer in the PA monomers. (Note) In all the codes used in this article, S indicates silicon.

3.2.5. Reason for the good effect of ester spacer (CO) on the oxygen permselectivity Although the size and size distribution of their molecular-sized spaces were roughly controlled by changing the shapes of pendant groups in the polymers, it is not easy to stabilize the spaces because

H. Jia et al. / Polymer 99 (2016) 695e703

dense polymer membranes usually are composed of amorphous polymers in rubber state where the molecules have high motion. Therefore their molecular-sized spaces are always changing, ie, dynamic. The change must lower permselectivities. The change of the space may be strongly affected by the motion of pendant groups which is largely governed by the flexibility of the spacer. In the case of CO spacer, the lower mobility than that of SO suppressed the motion of the pendant groups. Therefore the change of the space was suppressed and resulted in the good effect. 4. Conclusions Four novel substituted phenylacetylenes having a bulky fused polycyclic aliphatic group, i.e., pinanyl (Pi), adamantyl(Ad), or cholesteryl(Ch) via different kinds of spacers such as ester(CO) or silyloxy(SO), were synthesized, polymerized, and copolymerized with p-trimethylsilylphenylacetylene (SPA) to give soluble high molecular-weight polymers in high yields. The new five copolymers were able to be fabricated to self-standing membranes by solvent casting method. As a result, we can discuss the relationship systematically between bulky chemical structures and permeation behavior for the first time The oxygen permeation behaviors of the resulting membranes were measured together with other substituted phenylacetylenes having less bulky substituents such as menthyloxycarbonyl(MtCOPA) and ethyloxysilyl(EtSOPA) groups. In summary, the introduction of a spherical fused polycyclic aliphatic group, i.e., pinanyl (Pi) and adamantyl(Ad) were effective for obtaining membranes showing higher oxygen permselectivities. This may be because such spherical bulky groups can make molecular-sized spaces having low distribution in their size. About the spacers between the bulky groups(R) and the phenylacetylene(PA), ester(CO) was more effective for obtaining higher permselectivity maintaining similar permeability because of its rigid nature. Among all the ten polymer membranes in this study, Pi-containing polymers showed good performances, and particularly copolyPiCOPA was the best having more than 3.5 of a with high PO2 of more than 50 barrer. Unfortunately, these performances were inferior than those of polymers showing the best results reported in the literature. However, the information on molecular design of this study should be useful for designing polymers having much better performances in the future. Acknowledgements The work was supported by the new century excellent talents of Education Department of Heilongjiang Province of China (1253NCET-24). References [1] D.F. Sanders, Z.P. Smith, Energy-efficient polymeric gas separation membranes for a sustainable future, Polymer 54 (2013) 4729e4761. [2] N. Du, H.B. Park, Advances in high permeability polymeric membrane materials for CO2 separations, Energy Environ. Sci. 5 (2012) 7306. [3] T. Aoki, Macromolecular design of permselective membrane, Prog. Polym. Sci. 24 (1999) 951e993.

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