Nonsulfonated Diamines Research Articles

Stable covalent cross-linked polyfluoro sulfonated polyimide membranes with high proton conductance and vanadium resistance for application in vanadium redox flow batteries

Novel covalent cross-linked polyfluoro sulfonated polyimide membranes are developed by designing and synthesizing polyfluoro non-sulfonated diamine and adopting hydrophilic polyacrylic acid as the cross-linking agent for application in VRFBs.

Effect of Chemical Structure and Degree of Branching on the Stability of Proton Exchange Membranes Based on Sulfonated Polynaphthylimides.

Hydrolytic stability and oxidative stability are the core properties of sulfonated polynaphthylimides (SPIs) as proton exchange membranes. The chemical structure of SPIs directly influences the performance. Herein, three different series of branched SPIs were designed and prepared using 1,3,5-tris (2-trifluoromethyl-4-aminophenoxy) benzene as a trifunctional monomer and three non-sulfonated diamine monomers, such as 4,4′-oxydianiline (ODA), 2,2-bis[4-(4-aminophenoxy)phenyl]hexafluoropropane (6FODA), and 4,4′-(9-fluorenylidene)dianiline (BFDA). The effect of the chemical structure and degree of branching on SPIs properties is discussed. The results showed that by controlling the chemical structure and degree of branching, the chemical stability of SPIs changed significantly. SPI-6FODA with two ether linkages and a hydrophobic CF3 group has higher hydrolytic stability than SPI-ODA with only one ether linkage. In addition, with the increase of the introduced B3 monomer, the oxidation stability of SPI-6FODA has been greatly improved. We successfully synthesized SPIs with a high hydrolytic stability and oxidative stability.

Effect of non-sulfonated diamine monomer on branched sulfonated polyimide membrane for vanadium redox flow battery application

Branched sulfonated polyimide (bSPI) membranes based on three different non-sulfonated diamine monomers were fabricated for vanadium redox flow battery (VRFB) usage. Both FT-IR and 1H NMR spectra confirm that bSPIs were successfully synthesized. TGA results show that bSPI membranes have good thermal stability. FESEM pictures indicate that the surface of membrane in contact with catholyte keeps better integrity than that in contact with anolyte after 500-time cycling charge-discharge test. The water uptake, ion exchange capacity, mechanical strength of bSPI membranes are larger than or close to those of Nafion 117 membrane, and bSPI membranes exhibit remarkably lower vanadium ion permeability compared with Nafion 117 membrane. In addition, bSPI membranes have outstanding chemical stability in contrast with linear SPI membrane in ex-situ degradation test. Further, the bSPI (BAPP) membrane displays the best chemical stability and highest proton selectivity (1.23×105Smincm−3) among all bSPI membranes, thus it is seen as an optimum one for further single VRFB test. During 500-time cyclic charge-discharge test, the coulomb efficiency (CE: 97.1∼99.7%) of VRFB containing bSPI (BAPP) membrane is higher than that containing Nafion 117 (CE: 95.2∼98.6%) at 30∼120mAcm−2. The VRFB using bSPI (BAPP) membrane presents higher or comparable energy efficiency (EE) and capacity retention compared with that using Nafion 117 membrane at low or high current density. Based on the excellent physico-chemical properties and single cell performance together with much lower cost compared with widely used Nafion 117 membrane, the as-prepared bSPI (BAPP) membrane has great potential to be applied in VRFB.

Synthesis and characterization of sulfonated mutiphenyl conjugated polyimide for PEMFC

Abstract A new monomer, di-sulfuricacid-1,1-bis(4-aminophenyl)-2,2-diphenylethylene (SBAPDPE), was synthesized by direct sulfonation of the parent diamine, 1,1-bis(4-aminophenyl)-2,2-diphenylethylene (BAPDPE) using concentrated sulfuric acid. A series of the side-chain-type sulfonated conjugated tetraphenylethylene polyimides (SCTPPIs) with different degrees of sulfonation were prepared from dianhydrides with SBAPDPE and non-sulfonated diamine. The SCTPPIs generally showed good solubility in m-cresol and DMSO. The membranes were studied by FT-IR, 1H NMR spectroscopy, and TGA. Sorption experiments were conducted to observe the interaction of sulfonated polymers with water. The ion exchange capacity (IEC) and proton conductivity were evaluated with increase of degree of sulfonation.

Semi-fluorinated sulfonated polyimide membranes with enhanced proton selectivity and stability for vanadium redox flow batteries

A series of semi-fluorinated sulfonated polyimides (6F-SPIs) are designed and synthesized via a one-step high-temperature polycondensation reaction. The sulfonation degrees of 6F-SPIs are controlled through changing the ratio of sulfonated diamine to non-sulfonated diamine in the casting solution. The physico-chemical properties and single cell performance of 6F-SPI membranes are thoroughly evaluated and compared to a non-fluorinated SPI membrane (6H-SPI-50) and a Nafion 115 membrane. The results show that the designed 6F-SPI membrane with a 50% sulfonation degree (6F-SPI-50) possesses the highest proton selectivity (1.613×105Smincm−3) among all tested membranes. Besides, the 6F-SPI-50 membrane exhibits a promising performance for vanadium redox flow batteries (VRFBs), showing higher coulombic efficiencies (96.90–99.20%) and energy efficiencies (88.25–64.80%) than the Nafion 115 membrane (with coulombic efficiencies of 90.60–96.70% and energy efficiencies of 81.04–60.10%) at the current densities ranging from 20 to 100mAcm−2. Moreover, the 6F-SPI-50 membrane shows excellent chemical stability in the VRFB system. This work paves the way for the development of a new class of 6F-SPI membranes for the VRFB application.

Sulfonated polyimide copolymers based on 4,4′-diaminostilbene-2,2′-disulfonic acid and 3,5,3′,5′-tetramethylbenzidine with enhanced solubility

A new series of six-membered ring sulfonated polyimides with different combinations of two comonomers in the nonsulfonated diamine was prepared by one-step high-temperature polycondensation in m-cresol to improve the solubility of the resulting sulfonated polyimides. They are based on 1,4,5,8-naphthalenetetracarboxylic dianhydride, 4,4′-diaminostilbene-2,2-disulfonic acid sulfonated diamine, and equimolar mixture of 3,5,3′,5′-tetramethylbenzidine (TMB) and 4,4′-oxydianiline, bis(4-aminophenyl)methane, or bis(4-(aminophenoxy)-4-phenyl)isopropylidene nonsulfonated diamines. The introduction of TMB comonomer in the nonsulfonated diamine resulted in a remarkable improvement in the solubility of the resulting polyimides in comparison with the corresponding single-monomer nonsulfonated diamine polyimides. Flexible, transparent, and tough membranes were prepared by solution casting method from the different polyimides. The membranes were characterized with FTIR and 1H-NMR spectroscopy, differential scanning calorimetry, thermogravimetric analysis, water uptake, and ion-exchange capacity measurements. They exhibit high thermal stability and good correlation between the ion-exchange capacity and water uptake values.

Sulfonated polyimides containing triphenylphosphine oxide for proton exchange membranes

A series of sulfonated co-polyimides (co-SPI) were prepared by one pot polycondensation reaction of a combination of diamines namely; 4,4′-diaminostilbene-2,2′-disulfonic acid (DSDSA) and prepared non-sulfonated diamine (DATPPO) containing triphenylphosphine oxide with 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA). All these soluble co-SPI gave flexible membranes with high thermal stability and showed good mechanical property. Transmission electron microscopy (TEM) analysis revealed the microphase separated morphology with well-dispersed hydrophilic (cluster size in the range of 5–55 nm) domains. The co-SPI membranes showed high oxidative and hydrolytic stability with higher proton conductivity. All these co-SPI membranes exhibited low water uptake and swelling ratio. The co-SPI membrane TPPO-60 (60% degree of sulfonation) with IECW = 1.84 mequiv g−1 showed high proton conductivity (99 mS cm−1 at 80 °C and 107 mS cm−1 at 90 °C) in water with high oxidative (20 h) and hydrolytic stability (only 5% degradation in 24 h).

Synthesis and properties of branched sulfonated polyimides for membranes in vanadium redox flow battery application

Low-cost branched sulfonated polyimide (bSPI) membranes were prepared for vanadium redox flow battery (VRB) application. The degree of branching (DB) of membranes was controlled to be 0–12% through changing the mole ratio of branched non-sulfonated diamine to dianhydride. Both FT-IR and NMR spectra verified the successful preparation of bSPI membranes. The morphology was observed using SEM. Thermal and mechanical properties of bSPI-8 membrane were better than linear SPI. Chemical stability of bSPI membranes was higher than linear SPI. Both proton conductivity (2.97–4.53×10−2Scm−1) and vanadium ion permeability (4.51–12.23×10−7cm2min−1) of bSPI membranes increase with the DB. The bSPI-8 membrane with the highest proton selectivity and superior stability shows higher coulombic efficiency (CE, 97–99%) and energy efficiency (EE, 67–80%) than Nafion™ 117 membrane (CE, 95–98%, and EE, 62–73% respectively) at 50–120mAcm−2. Besides, the VRB with bSPI-8 membrane shows stable efficiency and good capacity retention during 800-cycle charge-discharge test. Therefore, the optimized bSPI-8 membrane is of great potential in VRB system because of its excellent battery performance and operational stability.

Structure–property correlation of semifluorinated 6-membered co-SPIs for proton exchange membrane

This article reports the synthesis, characterization and proton exchange membrane (PEM) properties of four new structurally different naphthalenetetracarboxylic dianhydride (NTDA)-based semifluorinated sulfonated copolyimides (co-SPIs) containing heterocyclic groups as well as phenyl ring with various catenation angles. To understand the structure–property correlation, the co-SPIs were prepared with a fixed sulfonation degree (70%, IEC∼2.1) by using the fixed molar feed ratio of sulfonated diamine to the different non-sulfonated diamines. The structures of the different co-SPIs, namely, p-DTN70, m-DTN70, DPyN70, and DThN70 were confirmed by FTIR and NMR spectroscopy. All the co-SPIs showed high thermal stability for 5% weight loss temperature (290–300°C) in synthetic air. Transparent, flexible and membranes were prepared from the co-SPIs that showed tensile strength in the range of 50–65MPa and Young’s modulus values in the range of 1.6–1.84GPa in wet condition. It was noticed that the dimensional and oxidative stability were higher for para-connecting co-SPI membrane (p-DTN70) than for meta-connecting membranes (m-DTN70, DPyN70 and DThN70). Whereas, the proton conductivity was found highest for meta-connecting m-DTN70 membrane (σ=79.2mS/cm at 90°C) due to the higher water uptake and better phase separated morphology of the membrane as observed by transmission electron microscopy analysis.

Synthesis and properties of novel multiblock copolyimides consisting of benzimidazole-groups-containing sulfonated polyimide hydrophilic blocks and non-sulfonated polyimide hydrophobic blocks as proton exchange membranes

A series of novel multiblock copolymers consisting of benzimidazole-groups-containing sulfonated polyimide hydrophilic blocks (averaged block length=20) and non-sulfonated polyimide hydrophobic blocks (averaged block length=5 or 10) have been synthesized via two-pot synthetic procedures. The anhydride-terminated hydrophilic oligomer is synthesized by copolymerization of excess 1,4,5,8-naphthalelnetetracarboxylic dianhydride (NTDA) with amine-terminated polybenzimidazole (PBI-NH2) and 4,4′-bis(4-aminophenoxy) biphenyl-3,3′-disulfonic acid (BAPBDS), while the amine-terminated hydrophobic oligomers are synthesized by polymerization of excess non-sulfonated diamines with NTDA or a fluorinated dianhydride. The resulting multiblock copolymers can be cast into tough membranes indicating that reasonably high molecular weights block copolymers have been obtained. The block SPIs exhibit microphase-separated structure, whereas the random one is amorphous. Fenton’s test reveals that the block copolymer membranes, in particular, those consisting of fluorinated hydrophobic blocks, are fairly stable toward radical oxidation. Preliminary fuel cell tests are performed to evaluate the fuel cell performance of the block copolymer membranes. The single cell equipped with the block copolymer membrane of which hydrophobic block is prepared from NTDA and a fluorinated diamine (averaged block length=5) exhibits a peak output power density of 0.70W/cm2 at 90°C and 92% relative humidity for H2/air which is comparable to that of Nafion 112.

Sulfonated polyimide membranes with different non-sulfonated diamines for vanadium redox battery applications

A series of vanadium ion blocking sulfonated polyimide (SPI) membranes with various non-sulfonated diamines were prepared for vanadium redox battery (VRB) applications. FT-IR spectrum verifies the successful synthesis of SPIs, FSEM images illustrate that the membrane surface facing the negative electrode is more intact than that facing the positive electrode. The properties of SPI membranes such as water uptake, ion exchange capacity, thermal stability, proton conductivity and vanadium ion permeability can be adjusted by the species and the structure of non-sulfonated diamine. All SPI membranes show over one or two order of magnitude lower permeability of vanadium ion (0.48 - 2.36×10−7cm2min−1) than currently used Nafion 117 membrane (17.10×10−7cm2min−1). Vanadium redox static batteries with SPI membranes exhibit lower self-discharge rate, higher coulombic efficiency (97% - 99%) compared with Nafion 117 (94%) at 30mAcm−2. Meanwhile, as-prepared SPI membranes are durable in 0.1molL−1 VO2++3.0molL−1 H2SO4 solutions at 40°C. All results show that SPI membranes are promising proton conductive membranes for VRB applications, among which the SPI (BAPP) has the best VRB performance.

Proton exchange properties of flexible diamine-based new fluorinated sulfonated polyimides

A series of new semifluorinated sulfonated polyimide copolymers (DHNHXX) were prepared from 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), 4,4′-diaminostilbene-2,2′-disulfonic acid (DSDSA) and 1,4-bis-[{2′-trifluoromethyl-4′-(4′′-aminophenyl)phenoxy}] benzene (HQA). The degree of sulfonation of DHNHXX was varied by changing the molar ratio of the sulfonated diamine, DSDSA to the non-sulfonated diamine, HQA. The flexible DHNHXX membranes showed high thermal stability (desulfonation temperature above 270 °C) and good mechanical properties. The oxidative stability of DHNHXX improved with increasing the fluorine content. DHNHXX showed anisotropic dimensional changes, and good water stability (did not dissolve for up to 415 h), higher than many other sulfonated polyimides. Transmission electron microscopy (TEM) analysis revealed cluster-like microstructures for the DHNHXX membranes, suggesting good phase-separated morphology. DHNH70 with IEC = 2.10 meq. g−1 exhibited high proton conductivity, with a maximum up to 129 mS cm−1 at 90 °C in water.

Synthesis and characterization of novel sulfonated polyimides from 4,6-bis(4-aminophenoxy)-naphthalene-2-sulfonic acid

A novel sulfonated diamine monomer, 4,6-bis(4-aminophenoxy)-naphthalene-2-sulfonic acid(BAPNS), was synthesized. A series of sulfonated polyimide copolymers was prepared from BAPNS, 1,4,5,8-naphthalenetetra-carboxylic dianhydride(NTDA) and nonsulfonated diamine 4,4′-diaminodiphenyl ether(ODA). Flexible, transparent, and mechanically strong membranes were obtained. The novel sulfonated polyimide(SPI) membranes show higher conductivity, for example, SPI-100 shows a conductivity of 0.0698 S/cm at 80 °C(SPI-X: X refers to molar fraction of BAPNS). The membranes exhibit the permeability of methanol from 2.18×10−7 cm2/s to 2.57×10−7 cm2/s, which is much lower than that of Nafion(2.00×10−6 cm2/s). The copolymers were thermally stable up to 330 °C. The sulfonated polyimide copolymers also show reasonable mechanical strength; for example, the maximum tensile strength at break of the sulfonated polyimide copolymer with 100%(molar fraction) BAPNS is 1.35 GPa under high moisture conditions. The optimum concentration of BAPNS was found to be 100%(molar fraction) from the view point of proton conductivity, methanol permeability, and membrane stability.

Structural influence of hydrophobic diamine in sulfonated poly(sulfide sulfone imide) copolymers on medium temperature PEM fuel cell

Sulfonated poly(sulfide sulfone imide) copolymers containing flexible sulfide bond and six-membered imide ring were synthesized by random polycondensation. Two types of membranes were prepared by using sulfide (S-PSI) and sulfide sulfone (S-PSFI) based non-sulfonated diamines to investigate the effects of the hydrophobic component. IECw values were controlled to 1.51−1.94 meq g−1 depending on the degree of sulfonation (DS) which was in the range of 50–80%. The membrane series showed good thermal stability up to 310 °C and mechanical properties (tensile strength >30 MPa). Dimensional stabilities were excellent with 23−35% increases, even at 100 °C. Proton conductivities of membranes composed of different hydrophobic diamines display a relatively good correlation with water content and morphology. In fuel cell tests, the S-PSI60 membrane shows relatively high current density of 250 mA cm−2 at 0.6 V and maximum power density of 175 mW cm−2 at 120 °C, 35% RH, 1.5 atm.

Synthesis, proton conductivity and chemical stability of novel sulfonated copolyimides-containing benzimidazole groups for fuel cell applications

A new diamine monomer, 2,2′-bis(4-aminophenyl)-5,5′-bibenzimidazole (BAPBI), has been simply synthesized via a one-step reaction procedure of 4-aminobenzoic acid and 3,3′-diaminobenzidine in polyphosphoric acid (PPA) at 190°C. A series of sulfonated copolyimides (SPIs)-containing benzimidazole groups have been prepared by random copolymerization of 1,4,5,8-naphthalenetetracarboxylic dianhydride, BAPBI, 4,4′-bis(4-aminophenoxy)biphenyl-3,3′-disulfonic acid and nonsulfonated diamines in m-cresol at 180°C. Transparent and tough SPI membranes are obtained by solution cast method. The SPIs show high decomposition temperatures (∼300°C) of sulfonic acid groups, indicating good thermal stability. Covalent cross-linking was successfully achieved by treating the SPI membranes in PPA at 170°C for 10 h. The covalently cross-linked SPI membranes show much improved radical oxidative stability due to the synergic action of the covalent cross-linking and the incorporation of benzimidazole groups into the polymer structure. The covalent cross-linking is also favorable for improving the hydrolytic stability of the SPI membranes. However, the proton conductivity decreased to some extent because the sulfonic acid groups had been partially consumed during the process of covalent cross-linking.

Synthesis and Characterization of Sulfonated Polyimides Containing Trifluoromethyl Groups as Proton Exchange Membranes

AbstractA novel sulfonated diamine, 4,4′‐bis(4‐amino‐3‐trifluoromethylphenoxy) biphenyl 3,3′‐disulfonic acid (F‐BAPBDS), was successfully synthesized by nucleophilic aromatic substitution of 4,4′‐dihydroxybiphenyl with 2‐chloro‐5‐nitrobenzotrifluoride, followed by reduction and sulfonation. A series of sulfonated polyimides of high molecular weight (SPI‐x, x represents the molar percentage of the sulfonated monomer) were prepared by copolymerization of 1,4,5,8‐naphathlenetetracarboxylic dianhydride (NTDA) with F‐BAPBDS and nonsulfonated diamine. Flexible and tough membranes of high mechanical strength were obtained by solution casting and the electrolyte properties of the polymers were intensively investigated. The copolymer membranes exhibited excellent oxidative stability due to the introducing of the CF3 groups. The SPI membranes displayed desirable proton conductivity (0.52×10−1–0.97×10−1 S·cm−1) and low methanol permeability (less than 2.8×10−7 cm2·s−1). The highest proton conductivity (1.89×10−1 S·cm−1) was obtained for the SPI‐90 membrane at 80°C, with an IEC of 2.12 mequiv/g. This value is higher than that of Nafion 117 (1.7×10−1 S·cm−1). Furthermore, the hydrolytic stability of the obtained SPIs is better than the BDSA and ODADS based SPIs due to the hydrophobic CF3 groups which protect the imide ring from being attacked by water molecules, in spite of its strong electron‐withdrawing behaviors.

Preparation and Properties of Sulfonated Polyimide Proton Conductive Membrane for Vanadium Redox Flow Battery

A series of sulfonated polyimides (SPIs) were synthesized by 1,4,5,8-naphthalene tetracarboxylic dianhydride (NTDA), 2,2′-benzidinedisulfonic acid (BDSA) and 4,4′- diaminodiphenyl ether (ODA) in m-cresol. The sulfonation degree of SPI was controlled through the ratio of sulfonated diamine to the non-sulfonated diamine, and the SPI membranes were prepared by a casting method. The chemical structures of SPI membranes were characterized by FT-IR. The properties of obtained SPI membranes were investigated, such as water uptake, ion exchange capacity, proton conductivity and permeability of vanadium ion. The proton conductivities of SPI membranes are ranged from 0.012 to 0.051 S/cm, and the permeabilities of vanadium ion are one or two orders of magnitude less than that of Nafion® 117 (1.80×10-6cm2/min ). Experimental results showed that SPI membranes are potential candidates for vanadium redox flow battery.

Sulfonated multiblock copolynaphthalimides for polymer electrolyte fuel cell application

Sulfonated multiblock copolynaphthalimides (multiblock co-SPIs) were prepared by two-pot polymerization method from 1,4,5,8-naphthalenetetracarboxylic dianhydride, sulfonated diamine of 4,4′-bis(4-aminophenoxy)-3,3′-bis(4-sulfophenyl)biphenyl (BAPSPB) and nonsulfonated diamine of 4,4′-diaminophenyl hexafluoropropane. The multiblock co-SPI (BA1) with hydrophilic/hydrophobic block length of 20/10 and ion exchange capacity (IEC) of 1.67 meq g −1 exhibited larger water uptake, larger in-plane and through-plane proton conductivity ( σ ∥ and σ ⊥ , respectively) than the random co-SPI with the similar IEC. The multiblock co-SPI (BA2) with the longer block length of 20/20 exhibited the large σ ∥ and σ ⊥ comparable to those of BA1, in spite of the smaller IEC of 1.35 meq g −1. Both the multiblock and random co-SPIs showed the moderate anisotropic proton conductivity ( σ ⊥/ σ //≒ 0.70) as well as anisotropic membrane swelling with about three times larger through-plane swelling than in-plane swelling. The TEM observation revealed that BA2 had an isotropic and inhomogeneous morphology with indistinct microphase-separated structure, whereas the random co-SPIs had a homogeneous morphology. The behavior of BAPSPB-based multiblock co-SPI membranes were quite different from that of the multiblock co-SPIs based on 2,2′-bis(4-sulfophenoxy)benzidine, which was due to the presence of two flexible ether bonds in BAPSPB moiety of the main chain. Even under the low humidification of 27/27% RH at 90 °C and 0.2 MPa, BA2 exhibited the fairly high PEFC performance; namely, cell voltage of 0.67 V at load current density of 0.5 A cm −2 and maximum output of 0.51 W cm −2, which were much larger than those of BA1 and the random co-SPI (RA1) with IEC of 1.84 meq g −1, and have the high potential as PEM for PEFC applications.

Sulfonated polyimides with flexible aliphatic side chains for polymer electrolyte fuel cells

A series of sulfonated polyimides (SPIs) were synthesized from a new side group sulfonated diamine, 2,2′-bis(4-sulfobutoxy) benzidine monomer (2,2′-BSBB), 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), and common nonsulfonated diamine monomers by polycondensation reaction. Membranes were prepared by casting their m-cresol solutions. The SPI membranes displayed proton conductivity σ values of 0.2–0.4 S cm −1 at 140 °C in liquid water and showed stronger relative humidity (RH) dependence of proton conductivity compared to that of Nafion 112. Most of the SPI membranes were both tough and flexible and thermally stable up to 230–250 °C. XRD spectra suggested the presence of crystalline structure in the membranes. TEM analysis indicated clear microphase separation structure between hydrophobic main chain and hydrophilic side chain. The fully humidified SPI membranes exhibited obvious anisotropic dimensional changes with much larger expansion in thickness than in plane. The long term proton conductivity stability (ca. 500 h) was confirmed at 140 °C. The methanol permeabilities ( P M ) of the SPI membranes were in the range of 4.0 × 10 −7–1.2 × 10 −6 cm 2/s with a 50 wt% methanol in feed at 30 °C, which were one order of magnitude smaller than that of Nafion 112. As a result, the membranes displayed much larger selectivity towards both high proton conductance and low methanol permeation, compared to Nafion 112, suggesting high potential application for direct methanol fuel cells (DMFCs).

Effect of Bridging Groups on Sulfonated Poly(imide-Siloxane) for Application in Proton Exchange Membrane

A series of six-membered sulfonated poly(imide-siloxane)s (SPIs) was synthesized using 1,4,5,8-naphthalenetetracarboxylic dianhydride (NTDA), aminopropyl-terminated polydimethylsiloxane (PDMS) 2,2-benzidinedisulfonic acid (BDSA), as the sulfonation target diamine groups, and various nonsulfonated diamine monomers behaving as bridging groups. The structure-property relationship of SPI-SXx membranes is discussed in detail according to the chemical structure of the various nonsulfonated diamines of the SPI-SXx membranes from the viewpoints of proton conductivity, ion exchange capacity (IEC), and membrane properties (water uptake and membrane swelling) at equal PDMS content SPI-SXx. The PDMS was introduced to enhance the proton conductivity and water uptake attributed from the high flexibility of the siloxane segments. The conductivity and water uptake of angled SPI-SXm and oxydianiline-based SPI-SX membranes (SPI-SXO) are greater than those prepared from diaminodiphenylmethane-based SPI-SX membranes (SPI-SXD) at a given IEC. These differences resulted from the increased number of entanglements of the SPI-SXx membrane. The SPI-SXD showed almost isotropically dimensional changes with the increase in water uptake, and the volume were slightly smaller than those estimated from the additivity rule. Free volume in the SPI-SXx increased with the increase in bulky irregular packing in nonsulfonated segments, which augmented the water uptake and, in turn, the conductivity of the polymer. With the increase in temperature, conductivity increased more rapidly in SPI-SXx than in Nafion 117. Microscopic analyses revealed that these smaller (<10 nm) and well-dispersed hydrophilic domains contribute to better proton conducting properties. The new sulfonated poly(imide-siloxane)s have proved to be a possible candidate as the polymer electrolyte membrane for polymer electrolyte fuel cells (PEFCs) and direct methanol fuel cells (DMFCs).