Structure, physical properties, and molecule transport of gas, liquid, and ions within a pentablock copolymer

The morphology and physical properties of a pentablock copolymer (PBC) were investigated as a function of sulfonation or ion-exchange capacity (IEC). This material is comprised t-butylstyrene (tBS), hydrogenated isoprene (HI), sulfonated polystyrene (sPS), and polystyrene (PS). Thermally reversible crosslinks are created with tBS, which is dispersed within a rubbery phase of HI, sPS, and PS. A morphology change was observed upon sulfonating PBC. This created abrupt material changes such as water swelling, proton conductivity, and methanol transport at an IEC greater than one. Water, proton, and methanol transport are associated with sPS domains. Gas transport occurs mainly through more permeable HI and tBS phases that were disrupted with increasing IEC. The permeability (P) was modeled using a lamellar morphology. Ion and methanol transport occurred via sulfonated domains. Finally, a structure–property and transport property correlation of this multi-block PBC ionomer is discussed within this paper.