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Synthesis and Gas-Transport Properties of Novel Copolymers Based on Tricyclononenes Containing One and Three Me3Si-Groups Pavel Chapala, Maxim Bermeshev,* Ludmila Starannikova, Victor Shantarovich, Natalia Gavrilova, Valentin Lakhtin, Yuri Yampolskii, Eugene Finkelshtein* In this work the authors report the preparation of new addition copolymers based on 3-trimethylsilyltricyclononene-7 (TCNSi1) and 3,3,4-tris(trimethylsilyl)tricyclononene-7 (TCNSi3). A number of high molecular weight copolymers are synthesized with the content of TCNSi3 units from 5 up to 20 mol% in the presence of catalyst Pd(OAc)2/[Ph3C]+[B(C6F5)4]− with the yields of 50%–80%. The obtained copolymers are amorphous. They possess large free volume elements (R3/R4) based on positron annihilating lifetime spectroscopy analysis and Brunauer–Emmett–Teller surface area n m up to 640 m2 g−1. Permeability coefficients of the obtained copolymers are determined for a wide range of gases He, H2, O2, N2, CO2, CH4, C2H6, C3H8, n-C4H10. The correlation between SiMe3 the content of TCNSi3 units and gas permeation parameters of Me3Si Me3Si SiMe3 the resulting copolymers is explored. It is found that the introSBET up to 640 m2/g duction of TCNSi3 moieties results in the rise in gas permeability of the corresponding copolymers. Moreover, increase in P(CH4) = 1540 Barrer TCNSi3 content in the copolymer leads to an increase of gas P(C4H10) = 14470 Barrer permeability.
Dr. P. Chapala, Dr. M. Bermeshev, Dr. L. Starannikova, Prof. Yu. Yampolskii, Prof. E. Finkelshtein A. V. Topchiev Institute of Petrochemical Synthesis RAS, 29 Leninskiy pr., 119991 Moscow, Russia E-mail:
[email protected];
[email protected] Prof. V. Shantarovich N. N. Semenov Institute of Chemical Physics RAS, 4 Kosygina str., 119334 Moscow, Russia Dr. N. Gavrilova D. I. Mendeleyev University of Chemical Technology of Russia 9 Miusskaya sq., 125047 Moscow, Russia Dr. V. Lakhtin State Scientific Center of the Russian Federation “State Research Institute for Chemistry and Technology of Organoelement Compounds” 38 Shosse Entuziastov, 111123 Moscow, Russia
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1. Introduction Membranes provide a way for efficient and energy saving gas separation.[1] Although inorganic membranes and mixed matrix membranes that contain inorganic additives attracted much attention of the researchers[2,3] it is namely polymer membranes proved the greatest feasibility for solving various complex problems of membrane gas separation.[4,5] During the last decade a lot of new polymers have been synthesized for this purpose and their properties have been studied.[6–12] As a result several classes of highly gas permeable polymers have been developed. Up to date the most useful approaches to new polymer membranes are the synthesis of homopolymers with appropriate side-groups and the structure of the
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DOI: 10.1002/macp.201600385
Synthesis and Gas-Transport Properties of Novel Copolymers Based on Tricyclononenes . . .
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main chains as well as the preparation of the composites based on them.[13–16] The development of copolymers with the well-defined monomer units structure seems to be also perspective. Thus, this approach could be especially useful in the cases where homopolymers could not be obtained at all or where the robust films of the corresponding homopolymers could not be prepared due to different reasons (e.g., poor solubility of the obtained polymers, low activity of polymerized monomers, low molecular weight of the obtained polymer, etc.). It allows one to estimate indirectly the impact of introduced comonomers on the resulting polymer properties (e.g., gas transport parameters, chain rigidity) and to obtain valuable correlations between the structure of the monomer unit and polymer properties. In this regard more active comonomers could be introduced and corresponding copolymers would be obtained. An example of the efficient use of copolymers was described by Tetsuka et al.[17,18] Addition type of poly norbornene with Si(OSiMe3)3-moieties was successfully synthesized, however, it was scarcely soluble in common organics. Copolymerization of Si(OSiMe3)3-containing norbornene with unsubstituted norbornene resulted in completely soluble polymers. The positive influence of the side Si(OSiMe3)3-groups in the corresponding copolymers on gas-transport properties was found. Thus, various type of copolymers for membrane gas separation such as copolyimides,[19–21] copolysulfones,[22] copolyacetylenes,[23,24] copolyacrylates,[20,25] and copolynorbornenes[17,18] have been synthesized and tested. An interesting example of random copolymers with great gas permeability are amorphous Teflons AF (copolymers of tetrafuoroethylene and cyclic comonomers perfluoro-2,2-dimethyle-1,3-dioxole).[26] It was shown that for these copolymers a linear correlation of the type logPm =a1·logP1 +a2·logP2 holds. Here P1 and P2 are the permeability coefficients of homopolymers with the structures corresponding to pure comonomers, a1 and a2 are their mole fraction and Pm is the permeability coefficient of a copolymer. In this way it was possible to estimate the permeability coefficient of the insoluble homopolymer of perfluoro-2,2-dimethyle-1,3-dioxole. Previously we have shown that the introduction of three SiMe3-groups directly attached to the norbornene structure (i.e., 3,3,4-tris(trimethylsilyl)tricyclononene-7) dramatically lowered monomer activity in metathesis polymerization in comparison with monomers containing only one or two SiMe3-groups.[27] At the same time we observed a significant increase in gas permeability of the corresponding metathesis polymer having three SiMe3-groups per a monomer unit. So in order to obtain polymers possessing higher gas permeability the introduction of three SiMe3-groups directly connected to the tricyclononene structure in a monomer unit is desirable. It seems that a preparation of copolymers with higher
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degree of substitution would allow one to overcome these difficulties and would be a reliable route to novel materials that combine high permeability and good selectivity. In this work we studied addition homo- and copolymerization of 3,3,4-tris(trimethylsilyl)tricyclononene-7 and gas transport properties of the obtained polymer materials in order to evaluate the effect of the introduction of the third SiMe3-group in the monomer unit of addition type of high molecular weight polynorbonenes.
2. Experimental Section 2.1. Materials All the chemicals were purchased from the commercial sources unless mentioned otherwise. Pd(OAc)2, [Ph3C]+[B(C6F5)4]− were purchased from Sigma-Aldrich and used without preliminary purification as toluene solution. Toluene was distilled over sodium under argon and it was kept in inert atmosphere (dried argon) with sodium/potassium alloy. 3,3,4-Tris(trimethylsilyl)tricyclononene-7 (TCNSi3) and 3-trimethylsilyltricyclononene-7 (TCNSi1) were obtained as described elsewhere.[28,29]
2.2. Methods of Polymer Characterization NMR spectra were recorded on a Bruker MSL-300 spectrometer operating at 300 MHz for 1H. Each sample was dissolved in CDCl3 up to a concentration of 10%. FTIR spectra were recorded on a FTIR-Microscope HYPERION 2000 Bruker associated with IFS-66 v/s Fourier spectrometer as ATR. Gel-permeation chromatography analysis of the polymers was performed on a Waters system with a differential refractometer (Chromatopack Microgel-5, toluene as the eluent, flow rate 1 mL min−1). Molecular mass and polydispersity were calculated by standard procedure relative to monodispersed polystyrene standards. Differential scanning calorimetry (DSC) was performed on a Mettler TA4000 system at a heating rate 20 °C min−1. Thermal gravimetric measurements (TGA) were carried out using a Perkin-Elmer TGA-7 instrument at a heating rate 10 °C min−1.
2.3. Addition Copolymerization of TCNSi3 and TCNSi1 The example is given for the synthesis of a copolymer containing 20 mol% of TCNSi3 units. The similar procedures were used for the copolymer synthesis with other content of TCNSi3 units. 50 wt% Toluene solution of 3,3,4-tris(trimethylsilyl) tricyclononene-7 (2.0 g, 2.97 mmol) was put into a Schlenk flask which was preliminary purged in vacuum and filled with argon. The solution was evaporated up to viscous liquid and a toluene solution of Pd(OAc)2 (5.2·10−3 mmol, 2.6 × 10−3 m), a toluene solution of [Ph3C]+[B(C6F5)4]− (16·10−3 mmol, 6.36 × 10−3 m) were added. The reaction mixture was stirred for 30 min and 3-trimethylsilyltricyclononene-7 (1.0 g, 5.20 mmol)
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was introduced into the reaction mixture. The resulting solution was stirred for one hour at 25 °C and then it was allowed to stay overnight at ambient temperature (25 °C). The obtained polymer was dissolved in toluene and it was precipitated by ethanol. The polymer was separated, washed by several portions of ethanol, and dried in vacuum. The polymer was twice reprecipitated by ethanol from toluene solution and dried in vacuum at 70 °C up to a constant weight. The polymer was obtained as white fibers. The yield was 50% (1.0 g). Mw = 3.4 × 105, Mn = 1.36 × 105. 1H NMR (CDCl ): 3.28-0.40 (m), 0.40-0.00 (m). 3 13C NMR (CDCl3): 53.53–38.30 (m), 34.01–26.69 (m), 27.75–20.21 (m), 3.70-(-)1.60 (m), -2.70-(-)4.30 (m). 29Si NMR (CDCl ): 3.68-2.07 (m), 1.90-0.39 (m), -1.62-(-)2.90 (m). 3 IR (cm−1): 2921, 2852, 1740, 1464, 1249, 1171, 1144, 1093, 1020, 959, 929, 831, 746, 685, 622. Elemental analysis for C30H56Si4 copolymer. Calculated for copolymer with 20 mol% TCNSi3 units: C, 71,73; H, 10,48; Si, 17.71. Found: C, 71.7; H, 10.7, Si, 17,61.
2.4. Membrane Preparation The identical conditions were used for the preparation of the samples for gas permeation and free volume investigations. The toluene solution of a copolymer (0.05 g mL−1) was intensively stirred for 24 h. After that it was filtrated into the cap with the bottom formed by stretched cellophane film. The solvent was allowed to evaporate at room temperature (4 d). Before the testing, the films were dried in a vacuum at room temperature until the constant weight is attained (2 d). No thermal treatment was applied. So, the total time for sample preparation was 6 d. The thickness of the films was in the range of 100–120 µm.
2.5. Positron Annihilating Lifetime Spectroscopy (PALS) The positron lifetimes were used to determine the effective sizes of free volume elements in the studied copolymers. This method is based on the measurement of lifetime spectra of positrons in polymers—lifetimes τi (ns) and corresponding intensities Ii (%). Longer lifetimes τ3 and τ4 (so-called o-ortho-positronium lifetimes) can be related to the mean size of free volume elements (FVE) in polymers using the Tao–Eldrup formula for infinitely deep spherically symmetric potential well
τ i = 1/2[1 − ( Ri /Ro ) + (1/2π )sin(2π Ri /Ro )]−1
2.6. Brunauer–Emmett–Teller (BET) Analysis The adsorption/desorption experiments were carried out at liquid nitrogen temperature (−196 °C) for N2 on a Micromeritics Gemini VI Surface Area Analyzer. All the samples were degassed at 25–50 mTorr, 100 °C for 10 h before measurements. The results were interpreted using Gemini VII software ver. 1.03.
2.7. Gas Permeation Measurements Permeability coefficients of the composites were determined using the gas chromatographic method. The steady state stream of penetrant at atmospheric feed pressure were continuously purged from feed to residue (retentate) side of the permeation cell, while the downstream part of it was swept by the gas-carrier (helium or nitrogen, the latter was used in measurement of permeation rate of He and H2). The permeability coefficients were determined by measuring the penetrant concentration in the gas-carrier and the total flow of this mixture. Partial pressure of the penetrants was close to zero in the downstream part of the cell. Temperature in the cell was 20–22 °C. It is important in such measurements to keep boundary conditions constant. This is achieved by appropriate flow rate in upstream and downstream parts of the cell. In a typical experiment (membrane surface area 3.46 cm2) upstream flow rate (tested gas) was 30 mL min−1, purge gas (He) below membrane was in the range 12–15 mL min−1, the flows of the penetrants through the membrane were: O2 0.17 mL min−1, CO2 0.77 mL min−1. So back diffusion can be neglected and boundary conditions were constant across the membrane.
2.8. Wide Angle X-Ray Diffraction (XRD) XRD experiments were carried out using two-coordinate AXS detector (Bruker) with the Cu Kα line (wavelength of 0.154 nm).
(1)
where τi =τ3 or τ4 are o-Ps lifetimes and Ri =R3 or R4 are the radii of FVE elements, expressed in ns and A, respectively; Ro =Ri + ΔR, where ΔR = 1.66 Å is the fitted empirical parameter.[30,31] The positron annihilation lifetime decay curves were measured at room temperature using an EGG@Ortec “fast–fast” lifetime spectrometer. A nickel-foil-supported [44Ti] titanium (IV) chloride radioactive positron source was used. Two stacks of film samples, each with a total thickness of about 1 mm, were placed on either side of the source. All the measurements were performed in inert (nitrogen) atmosphere. The time resolution was 300 ps (full width at the half maximum of the prompt coincidence curve). The contribution from annihilation in the source material, a background, and instrumental resolution
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were taken into account in the PATFIT program for treating the experimental lifetime data in four lifetime components. The resulting data were determined as an average value from the several spectra collected for the same sample, having an integral number of counts of at least 106 in each spectrum.
3. Results and Discussion 3.1. Addition Copolymerization of TCNSi3 and TCNSi1 Previously it was shown that the most active catalytic systems for the addition polymerization (AP) of Si-containing tricyclononene derivatives were Pd(OAc)2/[Ph3C]+[B(C6F5)4]− and Pd(OAc)2/[Ph3C]+[B(C6F5)4]−/PCy3.[6] However, the attempts to synthesize addition type of high molecular weight poly(3,3,4-tris(trimethylsilyl)tricyclononene-7) in the presence of these systems failed (Scheme 1A). Only oligomers in trace quantities were obtained in addition
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Scheme 1. A) The addition polymerization 3-trimethylsilyltricyclononene-7.
of
3,3,4-tris(trimethylsilyl)tricyclononene-7
homopolymerization of TCNSi3 even at low ratios of monomer/catalyst. The possible reasons for the low reactivity of TCNSi3 in addition polymerization are the steric hindrances caused by three bulky SiMe3-groups preventing chain propagation. The formation of robust films is a required characteristic of a polymer to investigate its gas transport properties. To achieve good mechanical properties for nonpolar polymers like silicon containing addition polytricyclononenes it is necessary to obtain high molecular weight materials. The addition of a more active and/or less hindered monomer into the reaction mixture would result in the formation of higher molecular weight copolymer products (Scheme 1B). In this work 3-trimethylsilyltricyclononene (TCNSi1) was chosen as a comonomer due to its high reactivity in AP and a close structure to the studied TCNSi3. The results of the copolymerization of TCNSi3 and TCNSi1 are presented in Table 1. As it can be seen from Table 1, the increase of the amount of the sterically hindered TCNSi3 in the initial monomer mixture led to the lowering both yield and molecular weight of the obtained copolymers while TCNSi3 content in the copoly mers increased. The rise of monomers/Pd(OAc)2 ratio with the constant TCNSi3/TCNSi1 ratio gave a decrease of a molecular weight and a polymer yield. For example,
and
B)
its
copolymerization
with
with the same molar feed ratio of TCNSi3 and TCNSi1, but with different catalyst concentration two different copolymers were obtained. At a higher monomer/catalyst ratio the polymer was obtained with a lower yield and lower molecular weights (Table 1, line 4) in comparison with the copolymer synthesized using the same catalytic system at higher concentration (Table 1, line 1). Probably, when the lower concentration of the catalyst is used the influence of adventitious impurities is more remarkable. The optimal conditions were found for the formation of high molecular weight copolymers possessing necessary film-forming properties. The copolymer composition was studied by elemental analysis because needed signals in 1H NMR spectra were not completely resolved. The obtained copolymers were soluble in common aprotic solvents such as benzene, toluene, chloroform, THF, etc. The synthesized copolymers possessed a good thermal stability (Figures 1, 1S in the Supporting Information) up to 300 °C in Ar and 240 °C in Air (5% of mass loss). The thermal stability did not depend from the copolymer composition and the corresponding TGA of the obtained copolymers curves are similar. The TGA analysis (Figure 2S, Supporting Information) of the polymer films prepared for gas-transport investigations indicated trace amounts of the residual solvent (toluene). The reason of
Table 1. The addition copolymerization of 3,3,4-tris(trimethylsilyl)tricyclononene-7 (TCNSi3) with 3-trimethylsilyltricyclononene-7 (TCNSi1).
Polymer code TCNSi3/TCNSi1/Pd(OAc)2/ Yield Mw·10−3 [Ph3C]+[B(C6F5)4]− [%]
Mn·10−3
Mw/Mn Polymer composition, Elemental TCNSi3 units [mol%] analysis Si [%]
CP(TCNSi3TCNSi1)-20
570/1000/1/3
50
342
136
2.5
20
17.61
CP(TCNSi3TCNSi1)-11
280/1000/1/3
67
378
145
2.6
11
16.40
CP(TCNSi3TCNSi1)-6
140/1000/1/3
80
444
177
2.5
6
15.30
CP(TCNSi3TCNSi1)-15
1830/3200/1/3
13
177
64
2.8
15
17.00
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Figure 1. TGA curves of a) CP(TCNSi3-TCNSi1)-6 in Ar/Air and b) CP(TCNSi3-TCNSi1)-20 in Ar.
a low solvent content in the films is the absence of polar groups in the studied copolymers as well as in the used solvent and thus there are no strong adsorption interactions between the copolymer and the solvent. The glass transition temperatures of the copolymers were not observed until the onset of thermal decomposition as DSC indicated.
3.2. Physico-Chemical Properties of the Synthesized Polymers Wide-angle X-ray diffraction (WAXD) indicated that the synthesized copolymers were completely amorphous as an
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example shows in Figures 2, 3S, 4S in the Supporting Information and Table 2. Two broaden peaks are presented on the WAXD patterns of copolymers. They are characteristic for highly gas permeable polymers. The left maximum of WAXD patterns of copolymers indicates relatively large d-spacing as it can be seen in Figures 2, 3S, 4S in the Supporting Information and Table 2. For all copolymers the location of the left maximum is the same. While there is a little shift of the right peak to the lower 2θ angles with the increase of TCNSi3 unit contents in copolymers. So, it can be concluded that introduction of TCNSi3 units into the polymer led to the increase of free volume. For example, the WAXD pattern of CP(TCNSi3-TCNSi1)-20 corresponds to the periodicity (d-spacing) of 6.3 and 15.2 Å, respectively, found via Bragg’s law dB = λ/(2sinθ). The second value of d-spacing can be considered as an indication of loose chain packing. The inter-chain distance (d-spacing) in the synthesized copolymers lies between the most permeable addition type polytricyclononene—PTCNSi2g where two SiMe3-groups located in geminal position and PTCNSi1 where only one SiMe3-group is present per a monomer unit. According to the WAXD it could be expected that CP(TCNSi3-TCNSi1)-20 would have higher permeability than PTCNSi1 but lower than PTCNSi2g. Investigation of the free volume in CP(TCNSi3-TCNSi1)-15, polymers was done by means of PALS (Table 3). As it could be seen from Table 3, the introduction of TCNSi3 units into a polymer led to an increase of τ4 lifetimes. Thus, the increase of TCNSi3 content in a copolymer resulted in the growth of R4, while R3 almost did not change. At the same time the corresponding intensities (I3, I4) were close to those in PTCNSi1. Specific surface area is another important parameter for pore size characterization which influences on gas transport mechanism. Adsorption/desorption curves of nitrogen of the obtained copolymers are presented in Figure 5S in the Supporting Information. There is a high uptake of nitrogen even at a low relative pressure. This indicates the presence of micropores for the copolymers. A somewhat higher uptake at low relative pressure for
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Figure 2. WAXD patterns of CP(TCNSi3-TCNSi1)-6 and CP(TCNSi3-TCNSi1)-15.
CP(TCNSi3-TCNSi1)-20 indicates that this polymer possesses higher specific surface area (Table 4). Based on the obtained experimental data, the main characteristics (specific surface area, pore size distribution, micropore volume) of porous materials were calculated. Surface areas were determined for the new Table 2. WAXD data for some of highly permeable polymers.
Polymer
CP(TCNSi3-TCNSi1)-20
(2θ)1
d1-spacing [Å]
(2θ)2
5.8
15.2
14
copolymers according to Brunauer–Emmett–Teller theory (Table 4). The obtained values are close to the BET surface area reported for PIM-1 (about 780 m2 g−1).[34] The copolymer with higher content of TCNSi3 units possessed higher specific surface area as well as higher values of micropore volumes calculated by different methods (Table 4). At the same time all the obtained values (BET surface area, Smicro, Vmicro) are higher than those d2-spacing characteristic for the less permeable [Å] polymer—PTCNSi1. These results are in good agreement with the data obtained via the PALS and WAXD analysis.
6.3
3.3. Gas-Transport Properties Before presenting the gas permeation parameters of the studied copolymers several words must be said about the trends of selectivity of different classes of polymers. It is well known that the permeability coefficient can be presented as P = D × S, where D is the diffusion coefficient and S is the solubility coefficient. For series of penetrants the P values can follow the trend of D or S. Most polymers (conventional glassy polymers) show size sieving selectivity, that is, the P values follow the changes of the diffusion coefficients D. However numerous polymers (rubbers and high free volume materials) show reverse
CP(TCNSi3-TCNSi1)-15
5.8
15.2
14.2
6.2
CP(TCNSi3-TCNSi1)-11
5.9
15.0
14.4
6.1
CP(TCNSi3-TCNSi1)-6
6.0
14.7
14.8
6.0
PTCNSi1[32]
6.0
14.7
15
5.9
PTCNSi2g[6]
5.6
15.8
13
6.8
PTMSP[33]
9.8
9.3
19
3.2
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Table 3. Free volume parameters of the studied copolymers according to PALS.
Sample
TCNSi3 unit content [%]
τ3 [ns]
τ4 [ns]
I3 [%]
I4 [%]
R3 [Å]
R4 [Å]
Volume of spherical larger FVE [Å3]
PTCNSi1a)
–
3.00
7.18
15.9
30.9
3.65
5.77
800
CP(TCNSi3TCNSi1)-6
6
3.28
7.68
18.7
30.2
3.82
5.82
825
CP(TCNSi3TCNSi1)-20
20
3.01
7.80
15.8
31.6
3.65
5.87
900
PTCNSi2g[6]
–
3.80
11.70
11.0
35.6
4.20
7.30
1400
The data were obtained for the polymer synthesized in the presence of Pd(OAc)2/[Ph3C]+[B(C6F5)4]− system.
a)
(or solubility controlled) selectivity, i.e., the P values follow the variation of the solubility coefficients S. This issue is extensively discussed in the literature.[35,36] In order to evaluate effects of the introduction of TCNSi3 units into the polymer structure upon gas transport properties the investigation of copolymer gas permeability was performed by gas-chromatographic method. The obtained results are presented in Table 5. The permeability coefficients were measured for permanent gases (He, H2, O2, N2, CO2) and for some of saturated hydrocarbons (CH4, C2H6, C3H8, n-C4H10). The gas permeability coefficients increase according to the following trend for permanent gases N2 < O2 ≈ He ≈ CH4 < H2 < CO2. Another interesting and potentially important feature of these copolymers is the observed solubility controlled permeation of hydrocarbons (Table 5). For conventional glassy polymers an increase in penetrante size results in a decrease in the permeability coefficients (size sieving effect).[38] For all synthesized copolymers an increase in n-alkane penetrante size results in the growth of permeability coefficients (i.e., P(CH4) < P(C2H6) < P(C4H10)) (Table 5). As it can be seen from Table 5, the introduction of the more bulky TCNSi3 units resulted in the increase of gas permeability. For example, the presence of 6 mol% of TCNSi3 units led to the growth of permeability coefficient P(O2) from 1040 up to 1100. Further increase of TCNSi3 content up to 20% gave an extra increase of gas permeability. Thus, permeability coefficient P(O2) increased up to
1400 Barrer (extra 36% in comparison with PTCNSi1) demonstrating nonlinear increase of gas permeability with the increase of TCNSi3 content. The same trends were observed for random copolymers of other classes.[17,18] Usually sharp growth of permeability was observed when the more rigid monomer unit content increased in copolymer composition. For example, it was shown that the increase of more bulky 5-tris(trimethylsiloxy) silylnorborne units (TMSONB) in random norbornene/5tris(trimethylsiloxy)silylnorborne copolymers resulted in nonlinear increase of oxygen permeability. The rise of TMSONB units from 9 through 18 up to 27 mol% led to permeability values of 39, 82, and 239 Barrer correspondingly.[18] The same phenomenon was observed for some other classes’ of copolymers (e.g., poly(sulfone-co-ethylene oxide)).[39] Many highly permeable polymers exhibit strong swelling and increases in free volume and gas permeability caused by insertion into nonsolvents like lower alcohols, e.g., polyacetylenes and SiMe3-containing polynorbornenes.[6,40] Because of this, certain experiments were conducted with the copolymer (CP(TCNSi3-TCNSi1)-20) studied in the present work. Table 5 shows that EtOH treatment induced increases in permeability coefficients for all the studied gases. This effect is more pronounced for the gases with larger molecular size. Solubility controlled selectivity is also obvious for EtOH treated sample. As it can be expected, highly gas permeable polymers exhibit comparatively moderate selectivities in
Table 4. Pore characteristics calculated using BET analysis.
TCNSi3 unit content [%]
BET surface area [m2 g−1]
Smicro [m2 g−1]
Vmicro [cm3 g−1], t-method
Vmicro [cm3 g−1], Dubinin– Radushkevich method
PTCNSi1[16]
0
610
180
0.07
0.25
CP(TCNSi3TCNSi1)-6
6
620
180
0.08
0.26
CP(TCNSi3TCNSi1)-20
20
640
230
0.10
0.27
PTCNSi2g[6]
–
790
280
0.12
0.32
Sample
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Table 5. Gas permeability coefficients (P) of the synthesized copolymers in comparison with some other highly permeable polymers.
P, Barrera)
Polymer He
H2
O2
N2
CO2
CH4
C2H6
C3H8
C4H10
1420
3070
1400
570
6800
1530
2230
2250
14 470
1700
3920
1790
800
8730
2140
3590
3570
20 960
CP(TCNSi3-TCNSi1)-6
1170
2720
1100
430
5530
1130
1630
1530
12 300
PTCNSi1b)
1180
2580
1040
400
5190
1040
1420
1470
13 380
3670
8600
4750
2650
19 900
6900
14 500
14 900
43 700
2630
16 700
9700
6300
34 200
15 400
26 000
30 300
78 000
CP(TCNSi3-TCNSi1)-20 (The first line “as cast”, the second line after EtOH)
PTCNSi2g PTMSP
[6]
[37]
a)1 Barrer = 10−10 cm3 (STP) cm cm−2 s−1 (cmHg)−1; b)The data were obtained for the polymer synthesized in the presence of Pd(OAc) / 2 [Ph3C]+[B(C6F5)4]− system.
Table 6. Separation factors for some gas pairs of the synthesized copolymers in comparison with some other highly permeable polymers α(Pi/Pj).
Polymer
O2/N2
CO2/N2
H2/N2
C4/C1
2.5
11.9
5.4
9.5
2.2
10.9
4.9
9.8
CP(TCNSi3-TCNSi1)-6
2.6
12.9
6.3
10.9
PTCNSi1
2.6
13.0
6.5
12.9
PTCNSi2g
1.8
7.5
3.2
6.3
[37]
1.5
5.4
2.7
5.1
CP(TCNSi3-TCNSi1)-20 (The first line “as cast”, the second line after EtOH)
[6]
PTMSP
comparison with conventional low permeable glassy polymers (Table 6). After EtOH treatment the selectivities of the sample changed rather weakly. Traditional trade-off effect holds between permeability and permselectivity as an analysis of Tables 5 and 6 shows: more permeable polymers demonstrate lower selectivity. It should be noted that all of the synthesized copolymers exhibited higher selectivities than PTCNSi2g. The selectivity for O2/N2 almost did not change with the increase of TCNSi3 content. The data presented in Table 5 allowed us to estimate the expected permeability coefficients of the homopolymer containing three SiMe3 groups. It was made by the same way as in the case of amorphous teflons AF.[26] The results of such, relatively rough estimates (because of wide extrapolation) are given in Table 7. Table 7. Permeability coefficients P (Barrer) and separation factors αij = Pi/Pj of the homopolymers with three SiMe3 groups.
P(O2)
P(N2)
P(CO2)
P(CH4)
4900 ± 1000
2570 ± 500
20 400 ± 1400
6760 ± 1400
α (O2/N2)
α (CO2/O2)
α (CO2/N2)
α (CO2/CH4)
4.2
7.9
3.0
1.9
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The results of this table show that in agreement with our previous observations[6,12,32] an increase in the number of bulky substituents leads to increases in gas permeability. Anticipated properties of this homopolymer put it in the family of the most permeable glassy materials such as polyacetylenes.[40] The trade-off behavior mentioned above reveals here even stronger than for the copolymers: separation factors decrease significantly as a comparison of Tables 6 and 7 shows.
4. Conclusions The synthesis of new addition copolymers based on Si-containing tricyclononenes was successfully accomplished. The obtained copolymers turned out to be highly permeable polymer materials with large free volume and high BET surface areas. The investigations of gas-transport properties of corresponding polymers were done for different gases (He, H2, O2, N2, CO2, CH4, C2H6, C3H8, n-C4H10). It was shown that the introduction of tricyclononene units containing three SiMe3-groups (TCNSi3) in copolymers resulted in the rise in gas permeability of the corresponding copolymers and revealed good selectivities toward various gas pairs, including solubility controlled selectivity for light
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hydrocarbons. The changes in gas permeability coefficients of the obtained copolymers had good correlations with BET, PALS, and WAXD data.
Supporting Information Supporting Information is available from the Wiley Online Library or from the author. Acknowledgements: The authors gratefully acknowledge the support of the Russian Science Foundation (Grant No. 14-19-01362). Received: August 7, 2016; Revised: October 1, 2016; Published online: November 28, 2016; DOI: 10.1002/macp.201600385 Keywords: addition polynorbonenes; gas permeation properties; membranes; silicon containing polymers; tricyclononenes
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