Tuning the Intermolecular Interactions of Sulfonated Ionomer Via Polymer Blending

Abstract

Morphology of proton exchange membranes defines the proton conductivity and the durability of the membranes. One cost-effective approach to manipulate the morphology of the sulfonated ionomers is via polymer blends. In this study, varying compositions of Penta Block Copolymers (PBC) with two different ion-exchange capacity (IEC) of 1.0 and 2.0 were blended with poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) to create 2wt% homogenous solution-cast membranes in chloroform. Unmodified PPO membrane possessed higher thermal decomposition temperatures of 427.41°C, and unmodified PBC(1.0) and PBC(2.0) decomposed at 399.85 °C and 400.805 °C, respectively. Both PBC(1.0)-PPO and PBC(2.0)-PPO blend membranes exhibited a similar trend for the changes in decomposition temperature with composition. As the PPO blend ratio increased, the decomposition temperature of PBC(1.0)-PPO and PBC(2.0)-PPO increased by 6.5% and 6.6%, respectively. These changes may be attributed to the increase in thermal stabilities due to PPO’s inherently high glass transition temperature. Water Uptake (WU) studies revealed that PBC(1.0) and PBC(2.0) membranes blended with PPO have reduced WU% as the PPO blend ratio increases. Unmodified PPO is highly hydrophobic and has a WU of 1.52%, while unmodified PBC(1.0) and PBC(2.0) portrayed WU of 14.44% and 74.5%, respectively. When hydrophobic PPO blends with the hydrophilic sulfonated ionomers, the ionic channels are hindered, lowering the WU%. For instance, WU of PBC (1.0)-PPO blend in the ratio of 50:50 is halved compared to PBC (1.0)-PPO blend of 90:10 ratio. Similarly, WU of PBC (2.0)-PPO blend in the ratio of 50:50 is lowered by 72.25% compared to PBC (2.0)-PPO blend of 90:10 ratio. In conclusion, the study shows that polymer blending significantly alters the membrane’s intermolecular interactions and changes the membrane’s durability and water uptake. The impact is more evident as the IEC of the sulfonated ionomers is increased. Proton conductivity studies and morphological transitions will be incorporated in future investigations. Figure 1