Ionic groups incorporated into a polymer have a decided effect on its physical properties. A number of ionomers and polyelectrolytes have been widely applied. In particular, sulfonated bisphenol‐A polysulfone (SPSF) has been used as a composite or single‐component membrane for the desalination of water. In this article, the synthesis and physical characteristics of sulfonated polysulfone are addressed. A detailed synthesis route is provided and methods that yield determinable levels of sulfonation are described. These ion‐containing polymers retain an excessive amount of residual salts, which, of course, are impurities to the system. Therefore, before any analyses were made the polymers were subjected to a thorough soxhlet extraction process with boiling water, which appeared to be quite effective. The degree of sulfonation was assessed by several methods such as 1H NMR and FT‐IR. A new 1H NMR method was derived because the method cited in the literature proved to be too inconsistent for our work. The new 1H NMR method used a quaternary ammonium counterion [N(CH3)4]. These methyl protons are easily measured and may be ratioed against the isopropylidene protons in the polymer backbone that act as an internal standard. Characterization of the physical properties of SPSF consisted of water uptake, differential scanning calorimetry (DSC), thermomechanical analysis (TMA), and solubility studies. Its physical appearance and mechanical behavior were improved by the solution procedure. Also addressed were the effects of different counterions (Na+ & Mg++) with SPSFs of low levels of sulfonation. The variation in physical properties between the divalent and monovalent counterions is dramatic, especially when observed by TMA in the rubber plateau above the apparent glass temperature.
SynopsisCellulose acetate (CA) and poly(bromopheny1ene oxide, dimethylphosphonate) (PI'OBrP), which are compatible polymers, have been cast from solution to give both dense and asymmetric alloy membranes. Membranes containing PPOBrP with different degrees of phosphonylation have heen prepared. The water absorption of these membranes increases with the number of phosphonate ester groups, but is kept in the range of 12-16 wt-O/o water for most of the alloy compositions, which contained 20-80 wt-% PPOBrP. The morphologies of asymmetric membranes obt,ained from various casting formulations were studied by scanning electron microscopy. Two different structures were identified: (1) the well-known dense skin resting on an open-celled foam, and (2) skin resting on a r)orous layer which displays a two-phase morphology. In the latter, dense spheres (0.1-1 gm) appear to grow out of a continuous polymer network. The membranes have been tested for hydraulic permeability and separation of water from salt solutions by reverse osmosis. In general, the asymmetric alloy membranes that had been annealed a t 90-95°C display salt rejections >90% and water permeation rates of 10-30 gfd. Since the phenyl ring of the PPOBrP component was brominated prior to membrane fabrication, the membranes exhibit exceptional tolerance to chlorinated water (20-80 ppm), as demonstrated in short-time durability tests. The irreversible collapse of these membranes occurs at. applied hydraulic pressures far above 1200 psi. A cross linking between the two polymer components in the membranes and some suggestions for further improvement of these membranes are also reported.
Tuning polymer-ion interaction strength is critical for balancing ion solvation and transport in solid polymer electrolytes for battery applications. In mixed Li+/electron conducting systems for improved battery binders, the design space is further complicated by seemingly opposing design rules for electron and ion conducting polymers. Conjugated polymers functionalized with cationic side chains have demonstrated high ionic conductivity, lithium transport, and electronic conductivity by combining long-range polymer ordering with diffuse ion interactions. Herein, we demonstrate a family of mixed conducting polythiophenes functionalized with a range of cationic side chains, namely imidazolium, trimethylammonium, and ammonium groups. The strength of ionic interactions and structure of the side chains govern lithium-selective transport, resulting in high Li+ conductivity (∼10–4 S/cm at 80 °C) and electronic conductivity. The more diffuse imidazolium ion affords labile ionic interactions, resulting in higher lithium transference than the other cations studied. Electronic conductivity is also higher in the imidazolium system, stemming from the ability of the planar side chains to stack while also accommodating the bulky TFSI– counterions. These results demonstrate the importance of interaction strength in ion transport while also indicating that the physical structure of the side chain has an impact on electronic conduction. The imidazolium group strikes a balance, achieving superior properties across all metrics.
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