Synthesis, Nanostructures and Properties of Sulfonated Poly(phenylene oxide) Bearing Polyfluorostyrene Side Chains as Proton Conducting Membranes

Abstract

Graft copolymers with ionic backbones and hydrophobic fluorinated side chains have been prepared by using lithiated poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) as a macroinitiator for anionic polymerization of 4-fluorostyrene. After grafting of the poly(4-fluorostyrene) (PFS) side chains, the PPO backbone was selectively sulfonated using trimethylsilylchlorosulfonate under mild and controlled conditions. Microscopy of solvent cast membranes revealed copolymer self-assembly into remarkably regular and well-ordered morphologies which, depending on the molecular structure, included lamellar and cylindrical arrangements of the proton conducting ionic nanophases. Thermal analysis indicated separate glass transitions of the PFS and PPO phases, and high thermal degradation temperatures of the membranes at approximately 220 and 300 °C for the H+ and the Na+ forms, respectively. The proton conductivity of fully hydrated acidic membranes was similar to that of Nafion, reaching above 0.2 S cm−1 at 120 °C. Compared at the same ion exchange capacity, the proton conductivity of the graft copolymer membranes was two times higher than that of a membrane based on an ungrafted sulfonated PPO. The study showed that it is possible to tailor and prepare proton-exchange membranes with well-ordered morphologies and high proton conductivity by employing graft copolymers with a sulfonated backbone bearing hydrophobic side chains.

Ion Transport by Nanochannels in Ion-Containing Aromatic Copolymers

“…For example, at 120°C, a membrane with a PA content of 57% achieved a conductivity of 4.6 mS/cm under nominally dry conditions and 93 mS/cm under 100% RH, as shown in Figure 7. 74 In addition, Jannasch and co-workers 76 used the anionic grafting-from technique to form graft copolymers with ionic backbones and hydrophobic fluorinated side chains (Scheme 4, 13). After grafting of the poly(4-fluorostyrene) (PFS) side chains, the PPO backbone was selectively sulfonated under mild and controlled conditions using trimethylsilylchlorosulfonate.…”

Ion transport in sulfonated polymers

“…8,20,30,33,58,65 This discovery stimulated several efforts of investigating the transport behavior of a range of sulfonated PEMs possessing nanoscale morphologies, and significantly improved transport properties were unanimously reported in a number of articles. 8,10,32,66 This observation has been rationalized in terms of the enhanced local concentration of ÀSO 3 H groups within the water channels of the nanostructured PEMs owing to confinement.…”

“…This can be rationalized as a consequence of different proximities of the sulfonic acid groups, where the closely located ionic moieties are beneficial for obtaining high conductivities. 15,33,36,58 Accordingly, efforts to locate the acid groups in close proximity via synthetic control or by morphological optimization have been widely described. 34,59 (3) In sulfonated polymers, there is an underlying source of polydispersity, originating from the dissimilar spatial distributions of the sulfonic acid groups.…”

Poly(arlyene ether sulfone) based semi-interpenetrating polymer network membranes containing cross-linked poly(vinyl phosphonic acid) chains for fuel cell applications at high temperature and low humidity conditions

“…The proton conductivity of SPAES could be increased by increasing the degree of sulfonation (DS), while the SPAES with high DS do not have high enough physical and chemical stability for PEMFC operation. Therefore, several approaches have been performed to prepare SPAES-based membranes having high proton conductivities with good physicochemical properties by preparing block copolymers [21], comb-likes polymers [22], and pore-filling structures based on SPAES with high DS [23]. Although they showed the improved properties, the drawbacks of these approaches includes the tedious synthetic procedures for the preparation of the polymers and the complicated process for the fabrication of the membranes.…”