Tetraarylphosphonium perfluorocyclobutyl polyelectrolyte with low critical surface energy, high thermal stability, and high alkaline resistance

Article abstract of DOI:10.1002/pola.29525

Two tetraarylphosphonium polyelectrolytes having perfluorocyclobutyl units in their backbones have been prepared in which the counteranion is either bromide (PFP·Br) or bis(trifluoromethyl)sulfonimide (PFP·NTf₂). These polymers exhibit high thermal stability as assessed by thermogravimetric analysis, with a decomposition temperature of 460 °C for PFP·NTf₂. Even after heating at 300 °C for 72 h, PFP·NTf₂ shows no signs of degradation detectable by nuclear magnetic resonance spectrometry. As is typical for many tetraarylphosphonium species, films of these polymers can be quite resistant to degradation by alkaline solution. Upon alkaline challenge by exposure to 6 M NaOH at 65 °C for 24 h, for example, only 16% of the phosphonium centers in PFP·NTf₂ are degraded, making PFP·NTf₂ one of the most alkaline-stable phosphonium polymers to date. Despite having ionic backbones, PFP·Br and PFP·NTf₂ exhibit very low critical surface energies of 26.1 and 22.9 mJ m^?1, respectively. These values are on par with the values for poly(vinylene fluoride) and dimethylsiloxane. Such low surface energy polycations capable of high alkaline stability may find application as components of alkaline fuel cell membranes.