Effects of sulfonate incorporation and structural isomerism on physical and gas transport properties of soluble sulfonated polyimides

Journal Pre-proof Effects of sulfonate incorporation and structural isomerism on physical and gas transport properties of soluble sulfonated polyimides Dajie Zhang, Jong Geun Seong, Won Hee Lee, Shinji Ando, Yinhua Wan, Young Moo Lee, Yongbing Zhuang PII:

S0032-3861(20)30103-8

DOI:

https://doi.org/10.1016/j.polymer.2020.122263

Reference:

JPOL 122263

To appear in:

Polymer

Received Date: 6 October 2019 Revised Date:

2 February 2020

Accepted Date: 5 February 2020

Please cite this article as: Zhang D, Seong JG, Lee WH, Ando S, Wan Y, Lee YM, Zhuang Y, Effects of sulfonate incorporation and structural isomerism on physical and gas transport properties of soluble sulfonated polyimides, Polymer (2020), doi: https://doi.org/10.1016/j.polymer.2020.122263. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Ltd.

Graphical Abstract

1

Effects of Sulfonate Incorporation and Structural Isomerism on Physical and Gas Transport Properties of Soluble Sulfonated Polyimides

2 3 4 5 6

Dajie Zhang,a Jong Geun Seong,b,1 Won Hee Lee,b Shinji Ando,c Yinhua Wan,a Young Moo Lee,b*

7

and Yongbing Zhuanga*

8 a

9

State Key Laboratory of Biochemical Engineering, Institute of Process Engineering, University of Chinese

10 11

Academy of Sciences, Chinese Academy of Sciences, Beijing 100190, PR China b

Department of Energy Engineering, College of Engineering, Hanyang University, Seoul 04763, Republic of

12

Korea c

13

Department of Chemical Science and Engineering, Tokyo Institute of Technology, Ookayama 2-12-1-E4-5,

14

Meguro-ku, Tokyo, 152-8552, Japan

15 16

1

17

*

18

E-mail: [email protected] (Y. Zhuang); [email protected] (Y. M. Lee)

Present address: Los Alamos National Laboratory, T004, Los Alamos NM 87545, United States

Corresponding authors:

19 20 21 22 23 24 25 26

1

1

Abstract

2

This study presents the effects of sulfonate incorporation and structural isomerism of soluble

3

sulfonated polyimides (SPIs) for potential membrane applications. The fluorinated dianhydride

4

(6FDA) and three commercially sulfonated diamines, 2,4,6-trimethyl-3,5-diaminobenzenesulfonic

5

acid (tDSA), 2,5-diaminobenzenesulfonic acid (pDSA), and 2,4-diaminobenzenesulfonic acid

6

(mDSA), were used to synthesize SPIs in a one-step polycondensation. The SPIs are soluble in

7

common organic solvents and have good mechanical properties as represented by tensile strength of

8

88.4 - 115.8 MPa and elongation at break of 10.3 - 15.2%. The resulting SPI membranes exhibit

9

low dielectric constants (∼2.61) and linear thermal expansion coefficients (CTE) ranging from 54.6

10

to 71.7 ppm/K. These SPI membranes have fractional free volume (FFV) of 0.119 to 0.148. The

11

sulfonation incorporation induced closer inter-chain packing, smaller FFV, larger CTE, higher

12

average refractive indices (nav), better transparency and higher ideal selectivities for almost all gas

13

pairs for their membranes. The para-linked TEA-pSPI membrane exhibited a larger inter-chain

14

d-spacing, larger FFV, larger CTE, smaller nav and slightly higher permeability coefficients than the

15

corresponding meta-linked TEA-mSPI membrane. This study guides molecular architecture for

16

improving particular membrane performance by introducing sulfonation groups as well as adjusting

17

either para- or meta-linkages into polymeric main chains.

18

19

Keywords: Polyimides; Sulfonation; Gas separation.

20

2

1

Introduction

2

Polyimides (PIs) have received much attention from academia and industry because of their

3

excellent mechanical, thermal, and chemical stability; electric and optical properties; and potential

4

for gas separation [1-10]. The design and development of multifunctional PI films with good

5

solubility, high optical transparency, low dielectric constant, and desired gas separation are

6

currently of intense interest [1, 4, 11, 12]. Indeed, numerous studies have shown that introducing

7

functional substitutions and isomerism of diamine or dianhydride monomers can be used to improve

8

polymer processability and other performance parameters for particular applications [13-19]. For

9

example, sulfonated polyimides (SPIs) with hydrophilic sulfonic acid groups have been successfully

10

synthesized to develop new proton exchange membrane materials as an alternative to

11

perfluorosulfonated ionomer (Nafion®) for fuel cell applications [9, 20, 21]. These SPIs may also be

12

used as membrane materials for gas separation [7, 10, 22, 23]. However, most of the SPIs

13

developed for fuel cells were not suitable for gas separation applications due to their low gas

14

permeability [8]. It has been challenging but is interesting to investigate the effect of sulfonic acid

15

on the properties of the resulting polyimides for membrane-based gas separation.

16

In the numerous studies of polyimide membranes, fluorine-containing polyimide membranes

17

have been identified as attractive and promising membrane materials because they showed high gas

18

permeability. This was attributed to the presence of bulky groups in the main chains that hinder

19

intra-segmental mobility, disrupt inter-chain-packing, and stiffen the backbone [3, 23-25]. Also,

20

research shows that adding fluorine-containing monomers in the backbones can increase the

3

1

solubility and processability of polyimides [26-29].

2

In addition, it is well known that bulky constituents play an important role in improving gas

3

permeability. Tanaka et al. investigated the effects of the substituents on gas permeability and

4

permselectivity [30]. The methyl substituents restrict internal rotation around the bonds between the

5

phenyl rings and the imide rings and decrease the efficiency of chain packing, resulting in increases

6

in both gas diffusion and gas solubility coefficients [31]. However, until now, the effects of sulfonic

7

acid groups in different substituent positions on the basic polymer properties such as optical

8

transparency, refractive index, chain orientation, linear coefficient of thermal expansion (CTE), and

9

dielectric constant have not been clear.

10

In previous studies, synthesis of sulfonated polyimides was usually carried out in m-cresol or

11

dimethyl sulfoxide solution [6, 8, 20, 22, 32-35]. Highly corrosive, highly irritating solvents limit

12

industrial production of SPIs. Therefore, it is better to find a non-irritating solvent with low toxicity

13

to prepare SPIs.

14

In

this

study,

4,4'-(hexafluoroisopropylidene)diphthalic

anhydride

(6FDA)

and

three

15

commercially sulfonated diamine monomers, 2,4,6-trimethyl-3,5-diaminobenzenesulfonic acid

16

(tDSA), 2,5-diaminobenzenesulfonic acid (pDSA), and 2,4-diaminobenzenesulfonic acid (mDSA),

17

were used to synthesize SPIs containing hexafluoroisopropylidene linkages (-C(CF3)2) by one-step

18

polycondensation in a low-toxicity solvent, N-methyl-2-pyrrolidinone (NMP), as shown in Scheme

19

1.

20

2,4,6-trimethyl-1,3-benzenediamine (tD) for comparison to the sulfonated polyimides. The

The

non-sulfonated

polyimide

was

4

synthesized

from

6FDA

and

1

solubility, mechanical strength, thermal stability, optical properties, refractive index, dielectric

2

constant, in-plane/out-of-plane birefringence, and gas transport characteristics were evaluated to

3

investigate the effects of sulfonate incorporation and structural isomerism on the physical properties

4

of the resulting polyimides. These SPI membranes are characterized by high toughness, good

5

thermal stability and low dielectric constant. Six single gases (He, H2, N2, O2, CH4, and CO2) were

6

used to investigate the effects of the substituents on single gas transport properties by comparing

7

them to commercial Matrimid® 5218 membranes [36, 37].

8 9 10

1. Experimental 2.1 Materials

11

Toluene (99.8%) and N-methyl-2-pyrrolidinone (NMP, >99.5%) were purchased from Aaddin

12

(Shanghai, China) and used as received. 4,4'-(Hexafluoroisopropylidene)diphthalic anhydride

13

(6FDA) was obtained from Sigma-Aldrich (Milwaukee, WI, USA) and purified by sublimation

14

before use. N,N-Dimethylformamide (DMF, 99.8%), dimethyl sulfoxide (DMSO, 99.8%),

15

triethylamine

16

2,4,6-trimethyl-3,5-diaminobenzenesulfonic acid (>98.0%),

17

(>98.0%), and 2,4-diaminobenzenesulfonic acid (>98.0%) were purchased from Tokyo Chemical

18

Industry (TCI, Tokyo, Japan) and used as received. Triethylamine (TEA, AR) was purchased from

19

Xilong Chemicals Industry (Guangdong, China).

(TEA,

>99%),

2,4,6-trimethyl-1,3-benzenediamine

20

5

(>98.0%),

2,5-diaminobenzenesulfonic acid

1

2

2.2 Preparation of sulfonated polyimides and non-sulfonated polyimides

The

SPIs

were

synthesized

from

6FDA

and

three

sulfonated

diamines,

3

2,4,6-trimethyl-3,5-diaminobenzenesulfonic acid (tDSA), 2,5-diaminobenzenesulfonic acid (pDSA),

4

and 2,4-diaminobenzenesulfonic acid (mDSA), as shown in Scheme 1 [8, 38]. The non-sulfonated

5

polyimide was synthesized from 6FDA and 2,4,6-trimethyl-1,3-benzenediamine (tD) for

6

comparison to the sulfonated polyimides. Using the preparation of 6FDA-tDSA as an example,

7

sulfonated diamine tDSA (3.4542g, 15 mmol) and NMP (101.18 mL) were added to a dry

8

three-necked flask equipped with a Dean-Stark trap and a condenser under nitrogen purge. In

9

addition, TEA (1.6696 g, 16.5 mmol) was added to improve the solubility of sulfonated diamines.

10

After all reagents were dissolved, a stoichiometric amount of 6FDA (6.6636g, 15 mmol) was added

11

into the mixture and stirred at room temperature overnight. Toluene was added to achieve a ratio of

12

NMP to toluene of 3:1, and the solution was heated to 80 oC for 4 h and 180 oC for 8 h. The warm

13

solution-containing product was poured into 200 ml methanol, and the powder precipitate was

14

filtered, washed with ethanol, and dried in a vacuum oven at 120 oC for 8 h to afford the TEA salt

15

forms of sulfonated polyimides (TEA-SPIs) as shown in Scheme 1. The polymerization procedure

16

for the other polyimides was similar to the above procedure.

6

1 2

Scheme 1. Synthesis of sulfonated polyimides and non-sulfonated polyimides.

3 4

tPI (Ar=tD). 1H NMR (600 MHz, DMSO-d6): δ = 1.91 (s, 6H), 2.13 (s, 6H), 2.30 (s, 6H), 13

5

7.38-7.12 (br, s, 2H), 7.93-7.91 (t, J = 3.0 Hz, 2H), 8.32-7.92 (d, J = 3.9 Hz, 2H).

6

MHz, DMSO-d6): δ = 165.80, 165.66, 138.28, 137.62, 137.32, 136.37, 132.57, 132.18, 130.11,

7

128.87, 128.18, 125.29, 124.63, 123.94, 39.50, 21.02, 17.65, 13.47. FTIR (ATR, ν, cm−1): 3476,

8

3393, 3235 (N-H stretching), 1787 (imide carbonyl symmetric stretching), 1722 (imide carbonyl

9

asymmetric stretching), 1355 (imide -C-N). Elemental Analysis for C28H16F6N2O4, Calculated: C,

10

60.21; H, 2.87; N, 5.02; Found: C, 59.27; H, 2.57; N, 5.51. Molecular weight, by gel permeation

11

chromatography (GPC), (DMF eluent, against polystyrene standards): Mn = 5.05 × 105, Mw = 7.12 ×

12

105, PDI =1.41.

13

C NMR (600

TEA-tSPI (Ar=tDSA). 1H NMR (600 MHz, DMSO-d6): δ = 1.92 (s, 6H), 2.18 (s, 6H), 2.44 (s, 13

C NMR (600 MHz, DMSO-d6): δ =

14

6H), 7.95-7.88 (t, J = 3.0 Hz, 2H), 8.18-8.04 (d, J , 2H).

15

165.92, 165.78, 162.28, 146.04, 137.78, 137.31, 135.94, 132.48, 132.08, 128.75, 63.27, 48.45,

16

45.75, 42.88, 39.50, 35.76, 30.74, 30.08, 28.98, 17.20, 16.82, 13.96, 8.61. FTIR (ATR, ν, cm−1):

17

3476, 3393, 3235 (N-H stretching), 1787 (imide carbonyl symmetric stretching), 1722 (imide

7

1

carbonyl asymmetric stretching), 1355 (imide -C-N). Elemental Analysis for C34H31F6N3O7S,

2

Calculated:

3

Molecular weight, by gel permeation chromatography (GPC), (DMF eluent, against polystyrene

4

standards): Mn = 3.85 × 105, Mw = 6.84 × 105, PDI =1.78.

5

C, 55.21; H, 4.19; N, 5.68; S, 4.33. Found: C, 53.99; H, 4.02; N, 6.73; S, 3.83.

TEA-pSPI (Ar=pDSA). 1H NMR (600 MHz, DMSO-d6): δ = 7.63-7.57 (br, s, 2H), 7.99−7.81 (t, 13

C NMR (600 MHz, DMSO-d6): δ = 166.04, 165.91,

6

J = 3.0 Hz, 2H), 8.22 (d, J = 3.9 Hz, 2H).

7

165.52, 162.28, 147.26, 137.42, 135.92, 133.64, 133.05, 132.75, 132.63, 131.49, 128.46, 128.02,

8

124.49, 124.35, 123.59, 123.48, 64.78, 64.61, 45.75, 39.50, 35.76, 30.75, 8.61. FTIR (ATR, ν,

9

cm−1): 3476, 3393, 3235 (N-H stretching), 1787 (imide carbonyl symmetric stretching), 1722 (imide

10

carbonyl asymmetric stretching), 1355 (imide -C-N). Elemental Analysis for C31H25F6N3O7S,

11

Calculated: C, 53.37; H, 3.59; N, 6.02; S, 4.59. Found: C, 53.33; H, 2.70; N, 6. S, 3.10; Molecular

12

weight, by gel permeation chromatography (GPC), (DMF eluent, against polystyrene standards): Mn

13

= 3.92 × 105, Mw = 6.47 × 105, PDI =1.65.

14

TEA-mSPI (Ar=mDSA). 1H NMR (600 MHz, DMSO-d6): δ = 7.71, 7.57,7.49 (br, s, 2H),

15

7.95−7.79 (t, J = 3.0 Hz, 2H), 8.18-7.99 (d, J = 3.9 Hz, 2H). 13C NMR (600 MHz, DMSO-d6): δ =

16

165.96, 165.80, 165.64, 165.53, 162.28, 137.35, 137.00, 135.96, 133.01, 132.60, 132.15, 129.02,

17

127.38, 126.18, 124.43, 123.58, 64.59, 45.75, 40.04, 35.76, 30.74, 17.20, 11.00, 8.61. FTIR (ATR,

18

ν, cm−1): 3476, 3393, 3235 (N−H stretching), 1787 (imide carbonyl symmetric stretching), 1722

19

(imide carbonyl asymmetric stretching), 1355 (imide -C-N). Elemental Analysis for

20

C31H25F6N3O7S, Calculated: C, 53.37; H, 3.59; N, 6.02; S, 4.59. Found: C, 54.56; H, 2.92; N, 6.62;

8

1

S, 4.07. Molecular weight, by gel permeation chromatography (GPC), (DMF eluent, against

2

polystyrene standards): Mn = 3.42 × 105, Mw = 6.29 × 105, PDI =1.84.

3 4

2.3 Membrane fabrication

5

Sulfonated and non-sulfonated polyimide membranes were prepared by casting polymer solutions

6

in DMF (5 wt.%) into a circular flat-bottomed glass dish. The glass dishes were placed in a vacuum

7

oven for 4 h and then slowly heated to 150 °C to evaporate the solvent by successive heating for 8 h.

8

The solvent was evaporated slowly, and triethylammonium salts of dry sulfonated polyimide

9

(TEA-SPIs) membranes were obtained.

10 11

2.4 Characterization

12

Nuclear magnetic resonance (NMR) spectra were recorded with a Mercury Plus 600 MHz

13

spectrometer (Varian, Inc., Palo Alto, CA, USA) using dimethyl sulfoxide-d6 (DMSO-d6) as a

14

solvent. Both the Fourier transform infrared (ATR-FTIR) spectra of the polymer powders and

15

attenuated total reflection mode ATR-FTIR spectra of the polymer membranes were measured

16

using an Infrared Microspectrometer (IlluminatIR, SensIR Technologies, Danbury, CT). Elemental

17

analyses were performed with a Thermofinnigan EA1108 (Fisions Instrument Co., Italy) elemental

18

analyzer. Molecular weight was measured by gel permeation chromatography (Waters GPC system,

19

Milford, MA) with polystyrene as an external standard and DMF as the eluent. Stress-strain curves

20

were obtained by testing the samples using a mechanical strength tester ESM301 from Mark-10

9

1

Corporation. Tests were performed at a rate of 2 mm/min. The mechanical properties for each

2

sample are based on the average value of at least three specimens. Thermogravimetric analysis

3

(TGA) was performed using a TGAQ50 instrument (TA Instrument, DE) at a heating rate of

4

10 °C/min under nitrogen. Dynamic mechanical analysis (DMA) was performed in the range of

5

50-500 °C with a heating rate of 10°C/min using a DMA Q800 (TA Instruments) in tensile mode at

6

1 Hz with a membrane sample area of 3 × 6 cm2. The glass transition temperatures (Tgs) of the

7

membranes were determined by their tanδ peaks. Wide angle X-ray diffractometry (WAXD) spectra

8

were recorded in reflection mode at room temperature using a Rigaku Denki D/MAX-2500 (Rigaku,

9

Japan) diffractometer with Cu Kα (wavelength λ = 1.54 Å) radiation. Densities of the membranes

10

were measured using a density measurement kit (Sartorius LA 120S, Sartorius AG, Goettingen,

11

Germany) by the buoyancy method. The liquid used for measurement was 2,2,4-trimethylpentane

12

(Sigma-Aldrich). Fractional free volume (FFV) was calculated as follows: Vsp =

Vf =

Vsp − 1.3 × VW Vsp

M

(1)

ρ = 1 - 1.3 ⋅

VW ⋅ ρ M

(2)

13

where Vsp is the molar volume of polymers derived from the measured density, M (g/mol) is the

14

molecular weight of the repeat unit, and Vw is the van der Waals molar volume based on Bondi’s

15

group contribution theory. Vw (cm3/mol) was estimated using the Synthia module from Materials

16

Studio 8.0 based on a group contribution method [39].

17

In-plane (nTE) and out-of-plane (nTM) refractive indices of the PI membranes formed on the silica

10

1

substrates were measured using a Prism Coupler (Metricon, PC-2010) at a wavelength of 1310 nm

2

at room temperature. Use of a near-infrared wavelength (1310 nm) effectively avoids the influence

3

of optical absorption in the visible region, which causes significant dispersion of the refractive

4

indices. The average refractive indices (nav) were calculated using Eq. (3), and the anisotropy of the

5

refractive index (i.e., the in-plane/out-of-plane birefringence (△n)), was calculated according to Eq.

6

(4). 2nTE + nTM 3 2

nav =

2

△n= nTE - nTM

(3) (4)

7

Linear thermal expansion coefficient (CTE) values along the film plane (xy) direction for the PI

8

specimens (10 mm long, 2 mm wide) in the glassy region were measured using thermomechanical

9

analysis (TMA) as an average in the range of 100 - 200 °C at a heating rate of 5 °C/min with a

10

thermomechanical analyzer (SHIMADZU TMA-60) and an appropriate load (typically 1.0 g for 20

11

mm thick films) in a dry nitrogen atmosphere. In this case, after the preliminary heating run up to

12

220 °C and successive cooling to room temperature in the TMA chamber, the data were collected

13

from the second heating run to remove any influence of adsorbed water. The average CTE value

14

was estimated from variation in length in the range of 100 - 200 °C according to the equation CTE100− 200 =

1 dl ⋅ l 0 dT

(5)

15

where T and l indicate the temperature and length of the PI film, respectively, and l0 indicates the

16

length at 100 °C.

17

Dielectric constants (ε) of the SPI membranes were estimated based on an empirical relation

11

1

using the average refractive index.

ε opt = 1.1nav 2

(6)

2

Water uptake of the SPI membrane was determined by measuring the change in weight before

3

and after hydration. The membrane was swollen in deionized water at room temperature for 24 h,

4

and then surface-attached water on the membrane was removed with filter paper. After that, the

5

wetted weight was determined as quickly as possible. The dried weight of the membrane was

6

determined after complete drying in a vacuum at 100 ◦C for 24 h. The water uptake was defined as

7

in the following equation: Water uptake (%) =

8

Wwet − Wdry × 100 Wdry

(7)

where Wwet and Wdry are the weights of wetted and dried membranes, respectively.

9

Gas permeabilities were obtained from a custom-made instrument using the time-lag method.

10

The test was performed at 35 °C and a feed pressure of 1 bar. Downstream pressure in a fixed

11

chamber volume was increased from 0 to 10 mmHg against 760 mmHg of upstream pressure. From

12

the slopes and intercepts in a steady state region of pressure increase as a function of time, gas

13

permeability coefficients were calculated using the following equation:

 273.15Vl  dp  P =   76T∆pA  dt

(8)

14

where P (Barrer) is the gas permeability, A (cm2) is the effective membrane area, l (cm) is

15

membrane thickness, T(K) is the measurement temperature, ∆p (cmHg) is the pressure difference

16

between upstream and downstream, and dp/dt is the rate of pressure rise in the downstream chamber

12

1

at steady state. The ideal selectivity (αx/y) for components x and y was defined as the ratio of gas

2

permeability of the two components. The diffusion coefficient D is calculated from the time-lag

3

apparatus using the following equation: l2 D= 6θ

(9)

4

Here θ is the “lag time.” In the case of He and H2, the very short lag time allows only an

5

estimation of the minimum limit of D, and the maximum limit of solubility coefficient, S [40], was

6

obtained indirectly via the equation

S=P D

(10)

7 8

2. Results and Discussion

9

2.1. Synthesis and solubility

10

Three polyimides containing sulfonated units, denoted as TEA-tSPI (Ar=tDSA), TEA-pSPI

11

(Ar=pDSA), and TEA-mSPI (Ar=mDSA) (Scheme 1), were synthesized by reaction of 6FDA with

12

the sulfonated diamines, trimethyl sulfonated diamine (tSDA), para-connecting sulfonated diamine

13

(pSDA), and meta-connecting sulfonated diamine (mSDA). The non-sulfonated polyimide [tPI

14

(Ar=tD)] was synthesized from 6FDA and 2,4,6-trimethyl-1,3-benzenediamine (tD) for comparison.

15

The chemical structures of all the resulting polyimides were confirmed by FTIR (Fig. 1), 1H NMR

16

(Fig. 2), 13C NMR spectra, and elemental analyses. High molecular weights greater than Mw = 6.29

17

× 105 g/mol with polydispersity of 1.65 - 1.84 were obtained by GPC (Table 1). The ATR-FTIR

18

(Fig. 1) and 1H NMR spectra (Fig. 2) and elemental analysis of TEA-SPIs supported the anticipated

13

1

chemical structures. Characteristic imide absorptions in the FTIR spectra (Fig. 1) appeared at ~1787

2

cm-1 (imide carbonyl symmetric stretching), 1722 cm−1 (imide carbonyl asymmetric stretching), and

3

1355 cm-1 (imide C-N stretching), confirming introduction of imide moieties in chain backbones.

4

The characteristic sulfonic group (S=O) absorption appeared at 1240 cm-1 [8]. Also, the

5

experimental elemental analysis results of the polyimides agreed well with the calculated values for

6

carbon, hydrogen, nitrogen, and sulfur, further confirming the designed polymer structures.

7 8

Table 1. Molecular weights and packing parameters of the TEA-SPIs and tPI. Polymer

Mna

M wa

-5

9 10 11 12

a

PDIa

-5

Mb

Vw c 3

ρd

FFV 3

(×10 )

(×10 )

(Mw / Mn)

(g/mol)

(cm /mol)

(g/cm )

tPI

5.05

7.12

1.41

558.437

258.326

1.3312

0.199

TEA-tSPI

3.85

6.84

1.78

739.686

360.619

1.3446

0.148

TEA-pSPI

3.92

6.47

1.65

697.605

330.862

1.4058

0.133

TEA-mSPI

3.42

6.29

1.84

697.605

330.862

1.4287

0.119

Gel permeation chromatography (DMF eluent, polystyrene standards).

b

M is the molecular weight of one repeat unit in the chain backbone.

c

Vw is the van der Waals molar volume.

d

Film density measurements were performed with an analytical balance.

Transmittance (%)

tPI TEA-tSPI TEA-pSPI TEA-mSPI

1787 1722

2100

13 14 15 16

1240 1355

1800 1500 1200 900 -1 Wavenumbers (cm )

600

Fig. 1. ATR-FTIR spectra of sulfonated polyimides (TEA-tSPI, TEA-pSPI and TEA-mSPI) and non-sulfonated tPI.

14

H2O

DMSO

4 3 1

5 7 6

2

-CH3(TEA)

3 2 1

5 4 6

12 5 4 6 3

546 123

9

8

7

6 5 4 Chemical shift (ppm)

3

2

1

1 2 3 4

Fig. 2. 1H NMR spectra (600 MHz, in DMSO-d6) of sulfonated polyimides (TEA-tSPI, TEA-pSPI, and TEA-mSPI) and non-sulfonated tPI.

5

Good solubility was one of the key parameters for industrial applications of the resulting SPIs in

6

common organic solvents because it is very important to easily prepare flexible and tough films

7

from solution casting [26, 41]. As shown in Table 2, the three TEA-SPIs are soluble in common

8

organic solvents such as DMSO, DMF, and NMP at room temperature.

9 10

15

Table 2. Solubility of fibrous TEA-SPI and tPI powders

1

Solvent Polyimide

2

acetone

THF

DMSO

NMP

DMF

methanol

ethanol

chloroform

tPI

＋＋

＋＋

＋＋

＋＋

＋＋

－－

－－

＋＋

TEA-tSPI

＋－

－－

＋＋

＋＋

＋＋

＋

－－

－－

TEA-pSPI

－－

－－

＋＋

＋＋

＋＋

－－

－－

－－

TEA-mSPI

－－

－－

＋＋

＋＋

＋＋

－－

－－

－－

Key: ‘++’ Easily soluble, ‘−−’ insoluble, ‘+’ soluble by heating, and ‘+ −’ partially soluble

3 4 5

3.2 Fractional free volume and polymer chain packing The free volume of polymer membranes may be estimated by density, positron annihilation 129

6

lifetime spectroscopy (PALS) [42] and

Xe NMR spectroscopy [42, 43]. Here we calculated

7

fractional free volume (FFV) by using measured density (Table 1). Film densities of the TEA-SPIs

8

were 1.3446-1.4287 g/cm3 (Table 1). Non-sulfonated tPI showed the expected high FFV value

9

(0.199). However, FFV values of sulfonated tSPI significantly decreased compared to that of the

10

corresponding non-sulfonated tPI membrane due to the strong interchain hydrogen bonds induced

11

by introduction of sulfonic substituents [30, 35]. Also, the trimethyl substituted TEA-tSPI

12

membranes revealed much higher FFV than non-methyl substituted TEA-pSPI and TEA-mSPI,

13

indicating that introducing methyl substitutions in the diamine increased steric hindrance and thus

14

FFV [31]. Additionally, the para-linked TEA-pSPI exhibited slightly higher FFV than the

15

corresponding meta-linked TEA-mSPI, similar to previous findings [19, 44, 45].

16

(a)

tPI TEA-tSPI TEA-pSPI TEA-mSPI

Intensity (a.u.)

A

B

5

10

(b)

15

20 25 2θ (°)

35

40

tPI TEA-tSPI TEA-pSPI TEA-mSPI

Intensity (a.u.)

A

B

5

1 2 3

30

10

15

20 25 30 35 40 2θ (°) Fig. 3. WAXD curves of sulfonated and non-sulfonated polyimides (TEA-tSPI, TEA-pSPI, TEA-mSPI, and tPI) for (a) membrane and (b) powder configurations.

4 5

As shown in Fig. 3, out-of-plane wide-angle X-ray diffraction (WAXD) measurements were

6

conducted to examine polymer chain packing. The peak positions and their calculated d-spacing

7

values are listed in Table 3. All polymer membranes exhibited two broad diffraction peaks, A and

8

B, located at about 2θ = 15.0° and 25.0°, respectively (Fig. 3a). The calculated d-spacing values of

9

peak A at about 2θ =15.0° (~5.9 Å) and B at 25.0° (~3.56 Å) likely correspond to the average

17

1

interchain packing in the ordered domains and the π-π stacking order, respectively [17, 19]. The

2

presence of π-π stacking implies that some planar and rigid aromatic heterocyclic rings in the

3

polymer backbones are arranged parallel to each other. This indicates the co-existence of some

4

ordered packing domains combined with primarily amorphous morphology domains in the

5

membranes. The amorphous phase provides special features to the polyimide, such as high

6

solubility in solvents and low modulus. From peak A, d-spacings of 5.29 Å, 5.77 Å, and 5.71 Å

7

calculated from peaks at 2θ = 16.73°, 15.35°, and 15.50° for the TEA-tSPI, TEA-pSPI, and

8

TEA-mSPI membranes were assigned to the interchain distances of the main chains in the

9

out-of-plane direction [46, 47].

10

However, d-spacings along the out-of-plane direction do not correspond to accurate molecular

11

packing in the membrane form. Chain aggregation is three-dimensionally homogeneous in the

12

powder form, and it provides a more reliable means of assessing the influence of chain structure on

13

d-spacing [48]. Fig. 3(b) shows the WAXD patterns of the powder states. As shown in Table 3, tPI

14

showed a broad diffraction peak at 2θ =15.02°. Compared with tPI, the TEA-tSPI powder showed

15

two diffraction peaks A and B located at 2θ = 17.01° and 23.57°, respectively. The position of the

16

diffraction peak of the TEA-tSPI was different from that of tPI, indicating that incorporation of

17

sulfonate changed the molecular lattice within the polyimides. The calculated d-spacing value of the

18

sulfonated TEA-tSPI powder (5.21 Å) was smaller than that of the corresponding non-sulfonated

19

tPI (5.89 Å), which is consistent with variation in FFV values. In addition, the para-linked

20

TEA-pSPI powder exhibited a slightly larger inter-chain d-spacing value (5.71 Å) than the

18

1

corresponding meta-linked TEA-mSPI membrane (5.64 Å), which agrees well with the variation of

2

their FFV values.

3 4 5

Table 3. Diffraction position (2θ) and d-spacing values in WAXD spectra of sulfonated and non-sulfonated polyimide membranes. d/Å

2θ /deg Polymer Membrane

Powder

Membrane

Powder

A

B

A

B

A

B

A

B

tPI

13.68

24.50

15.02

24.39

6.47

3.63

5.89

3.65

TEA-tSPI

16.73

23.66

17.01

23.57

5.29

3.76

5.21

3.77

TEA-pSPI

15.35

25.51

15.50

24.55

5.77

3.49

5.71

3.62

TEA-mSPI

15.50

25.35

15.70

25.85

5.71

3.51

5.64

3.44

6 7

3.3 Physical properties

8

Good mechanical properties are key factors for gas separation membrane applications. As shown

9

in Table 4 and Fig. 4a, all TEA-SPI membranes exhibited tensile strengths in the range of 70.1 -

10

115.8 MPa, an initial modulus of 0.80 - 1.40 GPa, and elongation at break of 10.3 - 15.2%,

11

indicating good mechanical properties. In particular, the TEA-tSPI membrane exhibited excellent

12

elongation at break of 15.2%, which is higher than those of non-sulfonated tPI (11.6%) and

13

sulfonated TEA-pSPI (10.3%) and TEA-mSPI (10.8%).

14

Thermal properties are critical for gas separation membrane applications, especially under harsh

15

environments such as elevated temperature. The thermal analysis data of the polyimides are

16

presented in Table 4 and Fig. 4b. As depicted in Fig. 4b, TGA curves of all SPIs exhibited similar

17

trends, and two main stages of weight loss were observed. SPIs are thermally unstable and start to

18

decompose at 240 °C, whereas conventional polyimides usually decompose around 500 °C [8]. The

19

1

first decomposition observed around a temperature range of 240 - 340 °C was attributed to removal

2

of -SO3Et3NH groups. The second stage of weight loss started at about 450 °C, where the main

3

chain of the polymers began to decompose [21, 49]. Char yields at 800 °C in nitrogen were higher

4

than 43%, and 5% and 10% of weight loss were observed at 311 - 488 and 337 - 511 °C,

5

respectively. In addition, all SPI membranes have glass transition temperatures (Tgs) of above

6

275 °C according to the DMA curves shown in Fig. S1.

7

Table 4. Properties of sulfonated and non-sulfonated polyimide membranes

8

tensile Polymer

9 10 11 12 13 14

tensile

elongation a

char

CTEc

b

water navd

△ne

εoptf

2.93

1.5281

0.0023

2.57

71.7

23.29

1.5342

0.0050

2.59

44

64.7

10.79

1.5418

0.0124

2.61

43

54.6

10.60

1.5466

0.0042

2.63

strength

modulus

at break

yield

(MPa)

(GPa)

(%)

%

tPI

70.1±9.3

0.80 ± 0.04

11.6±1.7

47

55.9

TEA-tSPI

88.4±4.6

1.07 ±0.07

15.2±2.6

43

TEA-pSPI

115.8±7.6

1.40 ±0.09

10.3±0.4

TEA-mSPI

99.3±4.1

1.20 ±0.07

10.8±0.6

(ppm/K)

a

Stress-strain obtained by testing the samples at a rate of 2 mm/min.

b

Residual weight retention when heated to 800 °C in nitrogen.

c

Thermal expansion coefficients.

d

Average refractive indices measured at 1310 nm.

e

In-plane/out-of-plane birefringence (1310 nm).

f

εopt =1.1 nav2.

15

20

uptake (wt.%)

120

(a)

Stress (MPa)

100 80 60 40

tPI TEA-tSPI TEA-pSPI TEA-mSPI

20 0

0

2

4

6 8 10 Strain (%)

12

14

100

Weight (%)

90 80 70 60 50 40

1 2 3

(b)

tPI TEA-tSPI TEA-pSPI TEA-mSPI

100 200 300 400 500 600 700 800 Temperature (℃ ) Fig. 4. (a) Typical stress-strain curves and (b) TGA curves of sulfonated and non-sulfonated polyimide membranes.

4 5

The coefficient of linear thermal expansion (CTE) is a key parameter required to estimate the

6

dimensional stability of PI gas separation membranes for high-temperature applications. The CTE

7

values were measured by TMA to further probe the thermal dimensional stability of these SPIs

8

(Table 4). Fig. 5 shows their in-plane thermal expansion behaviors. The TEA-SPI membranes

9

exhibited CTE values in the range of 54.6 - 71.7 ppm/K depending on chemical structures. In

10

general, thermal expansion of aromatic rings, imide rings, and covalent bonds along the PI chain are

21

1

negligibly small and are preferentially aligned in the film plane. In contrast, the thermal expansion

2

of non-covalent bonds and inter-chain interactions should be larger due to the segmental flexibility

3

and free volume expansion [50]. Sulfonated TEA-tSPI membranes exhibited larger CTE values than

4

the corresponding non-sulfonated tPI membranes due to incorporation of non-covalent -SO3Et3NH

5

groups. Also, sulfonated TEA-mSPI membranes exhibited lower CTE values than the

6

corresponding methyl TEA-tSPI membranes. The introduction of methyl substituents increased the

7

CTE values due to the reduced linearity. In addition, para-connecting TEA-pSPI membrane

8

exhibited larger CTE values than the corresponding meta-connecting TEA-mSPI membrane,

9

indicating that the meta-connecting form helps improve chain rigidity/linearity compared to the

10

para-connecting one for the SPI membranes.

In-plane expansion (%)

1.0 0.8

tPI TEA-tSPI TEA-pSPI TEA-mSPI

0.6 0.4 0.2 0.0 100

120

140 160 180 o Temperature ( C)

200

220

11 12 13 14

Fig. 5. In-plane thermal expansion behaviors of sulfonated and non-sulfonated PI membranes measured using the TMA method.

15

Note that the water uptake properties of the SPI membranes significantly affect transport

16

properties, such as decreasing methanol permeability or increasing O2/N2 selectivity [10, 22, 23].

22

1

The water uptake values of these polyimide membranes were summarized in Table 4. Obviously,

2

the water uptake of polyimides increased significantly with introduction of hydrophilic sulfonic acid

3

groups by comparing sulfonated TEA-tSPI with non-sulfonated tPI (Table 4). Moreover, the water

4

uptake of non-methyl-substituted TEA-SPIs (e.g., pSPI and mSPI) was significantly smaller than

5

that of trimethyl-substituted sulfonated TEA-tSPI [7, 8]. Also, as shown in Table 4, the water

6

uptake of pSPI was almost the same as that of mSPI, implying that isomerism has little effect on

7

water uptake for the SPI membranes.

8

To

investigate

anisotropic

orientations

of

non-sulfonated

and

SPI

membranes,

9

in-plane/out-of-plane birefringence (△n) was measured by the prism coupling method. As shown in

10

Table 4, all membranes exhibited low △n values in the range of 0.0023 to 0.0124 because of the

11

combined impact of low chain linearity that arise from introduction of hexafluoroisopropylidene

12

linkages (-C(CF3)2) into the chain backbones. The sulfonated TEA-tSPI membrane exhibited

13

slightly larger birefringence (0.0050) than the corresponding non-sulfonated tPI membrane (0.0023)

14

resulting from their higher chain rigidity due to strong inter-chain hydrogen-bonds [51, 52]. The △n

15

value of trimethyl-substituted TEA-tSPI was similar to that of the non-methyl TEA-mSPI. Also,

16

the para-linked TEA-pSPI exhibited higher △n values than meta-linked TEA-mSPI.

17

The refractive indices of these polyimide membranes measured at 1310 nm are listed in Table 4.

18

The TEA-tSPI exhibited slightly higher average refractive indices (nav =1.5342) compared to that of

19

the non-sulfonated PI membrane, tPI (nav =1.5281), from the same dianhydrides, probably due to

20

decreased FFV within the membranes. Also, the para-substituted TEA-pSPI showed smaller nav

23

1

than the corresponding isomeric meta-substituted TEA-mSPI due to higher FFVs within the

2

membranes.

3

In this study, the dielectric constants were estimated from the optical data on the basis of an

4

empirical relation [15, 53-55], εopt =1.1 nav2. The εopt values based on this relation are close to

5

dielectric constants (ε) determined with the capacitances at frequencies of 1 and 10 MHz for

6

polyimides and polybenzoxazoles in previous studies [56, 57]. Since the εopt values from empirical

7

relation eliminate the influence of dielectric anisotropy [54] as well as absorbed water [53], the

8

estimation by empirical relation has good reproducibility and practical applicability. Obviously, a

9

smaller nav value of the polymer membranes corresponds to a low dielectric constant according to

10

the empirical relationship [58]. The TEA-SPI membranes exhibited low dielectric constants in the

11

range of 2.59 - 2.63 (Table 4) depending on the chain structures. The tPI had smaller εopt value than

12

that of TEA-SPI due to higher FFV value. The εopt of TEA-mSPI (εopt = 2.63) was slightly larger

13

than that of TEA-tSPI with trimethyl groups (εopt = 2.59), and the para-substituted TEA-pSPI

14

showed slightly lower dielectric constant than the corresponding isomeric meta-substituted

15

TEA-mSPI.

16

Fig. 6 shows the UV-Vis spectroscopy results of these polyimide membranes. The high optical

17

transparency and colorless features of these polyimide membranes are shown in Fig. S2. The cut-off

18

wavelength is defined herein as the wavelength at which the transmittance is lower than 1% [59, 60].

19

The cut-off wavelength and transmittance (%) at 400 nm are listed in Table 5. Interestingly,

20

TMA-tSPI with a thickness of 51 µm was extremely transparent and very light in color (Fig. S2).

24

1

The light transmittance of TEA-tSPI membrane at 400 nm was 74.3%, which is significantly higher

2

than that of the non-sulfonated tPI membrane (69.3%). The methyl substituted TEA-tSPI membrane

3

showed higher light transmittance (74.3%) than the corresponding TEA-mSPI membrane and

4

TEA-pSPI membrane without methyl substituents (51.0% and 65.6%), which likely indicates a

5

reduction of intermolecular CTC caused by the bulky substituent groups. The sulfonate

6

incorporation can effectively increase the transparency of the membranes as well.

Transmittance / %

100 80 60 40 20

300 7 8 9

tPI TEA-tSPI TEA-pSPI TEA-mSPI

400

500

600

700

800

Wavelength / nm Fig. 6. UV-Vis spectra of TEA-SPIs (tSPI, pSPI and mSPI) and the non-sulfonated tPI for comparison.

10

Table 5. Optical properties of TEA-SPI membranes.

11

12

a

Polymer

tPI

TEA-tSPI

TEA-pSPI

TEA-mSPI

λcut off / nm

311

314

312

313

T400 /%a

69.3

74.3

65.6

51.0

Transmittance (%) at 400 nm (T400).

13 14

3.4 Single gas permeability

25

1

Single gas permeabilities for He, H2, N2, O2, CH4, and CO2 in sulfonated as well as

2

non-sulfonated polyimide membranes were measured to investigate the influence of the substituents

3

on chain packing and gas transport properties (Table 6). For the high FFV of non-sulfonated tPI,

4

the sequence in permeability coefficients from highest to lowest was CO2 > H2 > He > O2 > CH4 >

5

N2. For the trimethyl substituted TEA-tSPI membranes, the sequence in permeability coefficients

6

from highest to lowest was H2 > He > CO2 > O2 > N2 > CH4, which is slightly different from the

7

order of kinetic diameters of the penetrant gases, i.e., He (2.60 Å) < H2 (2.89 Å) < CO2 (3.30 Å) <

8

O2 (3.46 Å) < N2 (3.64 Å) < CH4 (3.80 Å). However, for the low FFV non-methyl substituted

9

TEA-pSPI and TEA-mSPI membranes, the sequence in permeability coefficients from highest to

10

lowest was He > H2 > CO2 > O2 > N2 > CH4, following the gas kinetic diameter order.

11

Moreover, gas transport properties of the three SPI membranes for six representative gas pairs

12

(H2/N2, O2/N2, CO2/CH4, CO2/N2, H2/CO2 and H2/CH4) are shown in Table 6 and Fig. 7. The

13

incorporation of sulfonate groups has important effects on gas transport of SPI membranes. As

14

confirmed in Table 6 and Fig. S3, the sulfonated TEA-tSPI membranes showed low permeability

15

values and diffusion coefficients compared to non-sulfonated tPI membranes due to decreased FFV

16

(tPI (0.199) > TEA-tSPI (0.148)) (Table 1) and d-spacing (Table 3) [35, 61].

17

In addition, chemical structures and isomerization can also play an important role in gas transport

18

change in SPIs. As presented in Table 6 and Fig. S3, trimethyl-substituted TEA-tSPI membranes

19

revealed much higher permeability coefficients than non-methyl-substituted TEA-pSPI and

20

TEA-mSPI membranes, which was attributed to higher diffusivity coefficients from higher FFV,

26

1

TEA-tSPI (0.148) > TEA-pSPI (0.133) > TEA-mSPI (0.119). This confirms that methyl substituents

2

can increase FFV within membranes. The para-linked TEA-pSPI exhibited slightly higher

3

permeability coefficients than the corresponding meta-linked TEA-mSPI for H2, N2, O2 and CO2

4

gases (Table 6). Also, it is noteworthy that the para-linked TEA-pSPI membrane had higher ideal

5

selectivity for the CO2/CH4 and H2/CH4 gas pairs. Furthermore, as shown in Table 6 and Fig. 7, for

6

N2, O2, CO2 and CH4 transport, all SPI membranes retained higher gas permeability values than the

7

commercial Matrimid® 5218. Gas transport results confirmed the influence of sulfonate

8

incorporation and structural isomerism on gas transport for SPI membranes. Introduction of

9

preformed sulfonic acid substituents obviously improved ideal selectivities for almost all gas pairs

10

(Fig. 7 and Fig. S4). Also, in comparison with membranes of non-sulfonated tPI, the trimethyl

11

TEA-tSPI membranes exhibited significantly higher ideal selectivity (Fig. S4).

12 13

27

1 2

Table 6. Single gas permeability, diffusivity, solubility, and ideal gas selectivity (α) for sulfonated polyimides (sPI) and conventional polyimides (tPI). Ideal selectivity (α) b Polymer

He

H2

N2

O2

CH4

CO2 H2/N2

O2/N2

CO2/CH4

CO2/N2

H2/CO2

H2/CH4

a

tPI

P

125

157

9.3

33

9.83

213

16.9

3.55

21.7

22.9

0.7

16

D

32664

16761

112

304

31.6

106

150

2.71

3.3

0.9

158

530

S

0.03

0.07

0.63

0.83

2.4

15.29

0.11

1.31

6.4

24.2

0.005

0.03

P

56.5

58.1

1.87

8.19

1.58

52.2

31

4.37

33

27.9

1.1

36.7

D

1769

1565

22.78

78.2

5.73

26.9

68.73

3.43

4.7

1.2

58.2

273

S

0.24

0.28

0.63

0.80

2.10

14.7

0.45

1.27

7.0

23.6

0.02

0.1

P

36

28.89

0.64

2.63

0.32

14

45

4.11

44

21.9

2.1

91

D

6452

1158

9.67

24.49

1.27

6.50

120

2.53

5.1

0.7

178

910

S

0.04

0.19

0.50

0.81

1.89

16.39

0.38

1.62

8.6

32.6

0.01

0.1

P

27.34

21.84

0.47

2.30

0.37

13.06

46.89

4.94

35.4

28

1.7

59

D

2731

1318

8.67

29

1.80

7.32

152

3.35

4.1

0.8

180

733

0.08

0.13

0.41

0.60

1.56

13.55

0.31

1.47

8.7

33

0.01

0.08

1.9

0.24

8.7

97

7.0

36

32

TEA-tSPI

TEA-pSPI

TEA-mSPI

S ®

Matrimid 5218[1]

P

3 4 5

a

22

27

0.27 −10

3

Units: P (Barrer), 10 cm (STP)/cm s cmHg; D, -10 measured at 1 atm, 35 °C. b Ideal selectivity (α = P1/P2).

28

−9

2

3.9 3

130 3

cm /s; and S, cm (STP)/cm atm,

1000

100

Matrimid TEA-pSPI

100

(b)

Selectivity H2/N2

Selectivity H2/CH4

(a)

TEA-mSPI TEA-tSPI

TEA-mSPI TEA-pSPI TEA-tSPI tPI

tPI

10

10

10 100 1000 Permeability H2 (Barrer)

10 100 1000 Permeability H2 (Barrer)

(c)

(d)

Selectivity CO2/CH4

Selectivity H2/CO2

10

100

Matrimid TEA-pSPI TEA-mSPI TEA-tSPI

1

TEA-pSPI

Matrimid TEA-mSPI TEA-tSPI tPI

tPI

10 10 100 1000 Permaeability H2 (Barrer)

12 10

(e)

Matrimid TEA-mSPI TEA-pSPI

Selectivity O2/N2

Selectivity CO2/N2

100

TEA-tSPI tPI

10

0.1

1

Matrimid

1

10 100 Permeability CO2 (Barrer)

(f)

8 Matrimid

6 TEA-mSPI

4

TEA-pSPI

TEA-tSPI tPI

2 0.1

1 10 100 1000 Permeability CO2 (Barrer)

1000

1 10 100 Permeabilty O2 (Barrer)

1000

2

Fig. 7. Robeson plots relevant to sulfonated polyimides (SPI) (■), conventional polyimides tPI ( ),

3

and Matrimid® 5218 ( ) properties for (a) H2/CH4, (b) H2/N2, (c) H2/CH4, (d) CO2/CH4, (e) CO2/N2,

4

and (f) O2/N2 gas pairs.

5 6 7

29

1

4. Conclusions

2

Three SPIs, TEA-tSPI, TEA-mSPI, and TEA-pSPI, were synthesized via a high-yield one-pot

3

route from commercially available starting monomers. The non-sulfonated polyimide was also

4

synthesized for comparison to the SPIs. The SPIs are soluble in common organic solvents such as

5

DMSO, DMF, and NMP. They have good mechanical properties as represented by tensile strengths

6

of 88.4 - 115.8 MPa and elongation at break values of 10.3 - 15.2%. The SPI membranes exhibit

7

low dielectric constants (∼2.61) and low linear thermal expansion coefficients (CTE) ranging from

8

54.6 to 71.7 ppm/K. These membranes have fractional free volume (FFV) values of 0.119 to 0.148.

9

The water uptake of SPI membranes in terms of wt.% varied from 10.6 to 23.29. The average

10

refractive indices (nav) at 1310 nm varied from 1.5342 to 1.5466. The membranes exhibited visible

11

wavelength transparency (%) at 400 nm equal to 74.3, 73.4 and 65.6%, respectively, for TEA-tSPI,

12

TEA-pSPI and TEA-mSPI. Also, all SPI membranes exhibited higher gas permeability than the

13

commercial Matrimid® 5218. The resulting SPIs exhibited an excellent combination of properties,

14

such as good ideal selectivity and moderate permeability, due to introduction of sulfonated group

15

into the polyimides.

16

The effects of sulfonate incorporation and structural isomerism on the chain packing, physical

17

properties and gas transport of the resulting polyimides were evaluated. The introduction of sulfonic

18

acid groups induced closer inter-chain packing, smaller FFV, larger CTE, higher average refractive

19

indices (nav), better transparency and higher ideal selectivities for almost all gas pairs for their

20

membranes. The para-linked TEA-pSPI membrane exhibited a larger inter-chain d-spacing, larger

30

1

FFV, larger CTE, smaller nav and slightly higher permeability coefficients than the corresponding

2

meta-linked TEA-mSPI membrane.

3 4

Declaration of competing interest

5

The authors declared that they have no conflicts of interest to this work. We declare that we do not

6

have any commercial or associative interest that represents a conflict of interest in connection with

7

the work submitted.

8 9

CRediT authorship contribution statement

10

Dajie Zhang: Methodology, Investigation, Data Curation, Writing - original draft. Jong Geun Seong:

11

Investigation, Visualization, Writing - review & editing. Won Hee Lee: Investigation. Shinji Ando:

12

Investigation. Yinhua Wan: Funding acquisition. Young Moo Lee: Supervision, Writing - review &

13

editing. Yongbing Zhuang: Supervision, Conceptualization, Writing - review & editing.

14 15

Acknowledgements

16

This work was supported by the Foundation for “Hundred Talent Program” and Open Fund of the

17

State Key Laboratory of Biochemical Engineering, Institute of Process Engineering (IPE), Chinese

18

Academy of Sciences (CAS). This research was also supported by the Technology Development

19

Program to Solve Climate Changes through the National Research Foundation of Korea (NRF)

20

funded by the Ministry of Science and ICT (NRF-2018M1A2A2061979). J.G.S. also acknowledges

31

1

support for his fellowship as a Postdoctoral Research Associate and a Research Assistant Professor

2

by the World Class Department Program at Hanyang University, a President-funded program of

3

Hanyang University to build a flagship department and develop manpower.

4 5 6

Appendix A. Supplementary data Supplementary data to this article can be found online at at http://

7 8

AUTHOR INFORMATION

9

*Corresponding authors

10

*(Y. Zhuang) E-mail: [email protected];

11

*(Y.M. Lee) E-mail: [email protected]

12

Notes

13

The authors declare no competing financial interests.

14 15

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40

Highlights The SPIs were synthesized by a one-step polycondensation in a low-toxicity NMP. The SPI membranes exhibited high toughness, good thermal stability and low dielectric constant. Single gas permeability of the SPI membranes was evaluated. Effects of sulfonate incorporation and structural isomerism of the SPIs were proposed.

CRediT authorship contribution statement Dajie Zhang: Methodology, Investigation, Data Curation, Writing - original draft. Jong Geun Seong: Investigation, Visualization, Writing - review & editing. Won Hee Lee: Investigation. Shinji Ando: Investigation. Yinhua Wan: Funding acquisition. Young Moo Lee: Supervision, Writing - review & editing. Yongbing Zhuang: Supervision, Conceptualization, Writing - review & editing.

Declaration of interests ☒ The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. ☐The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: