Synthesis and characterization of sulfonated fluorinated block copolymer membranes with different esterified initiators for DMFC applications

Abstract

This investigation studied the synthesis of ionic membranes composed of a sulfonated poly(styrene‐isobutylene‐styrene) with novel fluoroblock copolymers. These fluoroblock copolymers were synthesized using three different initiators by Atom Transfer Radical Polymerization (ATRP); two fluoroinitiators were obtained from the esterification of 2‐(perfluoroalkyl) ethanol or octafluoro 4‐4′‐biphenol. The third initiator evaluated was 1‐bromoethyl benzene. The resulting block copolymers were characterized using several techniques: Gel Permeation Chromatography, Nuclear Magnetic Resonance, Fourier Transform Infrared Spectroscopy, Ultraviolet Spectroscopy, Thermogravimetric Analysis, and Differential Scanning Calorimetry. Transport properties (e.g., proton conductivity and methanol permeability) were measured to evaluate their performance for direct methanol fuel cell (DMFC). The choice of ATRP initiator was found to have a profound impact on the thermal stability of the different homopolymers and block copolymers studied. In addition, the chemical nature and symmetry of the initiators can lead to different chemical and electronic transitions, which influence the performance of these ionic membranes in applications such as proton exchange membranes for DMFC applications. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2015, 132, 42046.

Effect of block composition on the morphology and transport properties of sulfonated fluoroblock copolymer blend membranes

“…It should be noted that the relative increase in methanol permeability at higher fluoropolymer composition (70%) is not as large as the increase in proton conductivity (418%). Although the transport mechanism for protons and methanol is similar, studies suggest that the methanol permeability is more sensitive to free volume and to changes in chemical composition, while changes in morphology could lead to more significant differences in the transport mechanism of both protons and methanol .…”

“…However, the maximum value of methanol permeability was reached at a higher correlation length. Studies suggested that variations between the proton conductivity and methanol permeability in SIBS SO 3 H are related to competing effects that depend on the free volume . Figure shows the relationship between the proton conductivity, water content, IEC, correlation length for hydrated membrane, and polymer percent of PHFBMA.…”

“…SIBS was purchased from Kaneka ® (30 wt% polystyrene and M n 65,000 g/mole). PS‐b‐PHFBMA was synthesized following the procedure of a previous study (9 wt% Zonyl ® , 55.52 wt% PS, 35.5 wt% PHFBMA, and M n 11,800 g/mole). Chemicals used for the sulfonation of SIBS and the membrane casting included: sulfuric acid (Sigma Aldrich, 95–98%), acetic anhydride (Aldrich Chemical, 99+ %), hexyl alcohol (Acros Organics, 98%, extra pure), methanol (Fisher Scientific, 99.9%), toluene (Fisher Scientific Optima, 99.8%), and dichloromethane (Fisher Scientific, Optima 99.9%).…”

“…However, membranes blending SIBS SO 3 H with an ion‐containing fluoropolymer may reduce the methanol permeability without reducing the proton conductivity. This is, because the additional ionic domains may allow for different transport mechanisms for protons and methanol .…”

Polymer Nanocomposite Membranes of Sulfonated Poly(Styrene‐Isobutylene‐Styrene) With Sulfonated Graphene Oxide for Fuel Cell and Protective Clothing Applications

“…Some studies have suggested that this behavior also occurs due to a reduction in P MeOH attributed to reduced dimensions of ionic clusters and interfacial interactions between fillers and the functionalized polymer [12,29]. The methanol permeability of a PEM is usually influenced by its morphology [61]. However, no correlation is observed between P MeOH and the morphology of the PEMs.…”