Synergistic enhancement in mechanical properties and microstructure of homoblends made of poly(styrene-co-styrenesulfonic acid) and poly(styrene-co-4-vinylpyridine)

Bulk mechanical properties and microstructure of a model blend (homoblend), made of poly(styrene-co-styrenesulfonic acid) (SPS) and poly(styrene-co-4-vinylpyridine) (SVP), were investigated by tensile measurements and modulated differential scanning calorimetry (MDSC). The mechanical properties exhibited synergism: tensile strength and toughness values of the blends were higher than those expected based on the rule of mixtures. The results were attributed to the formation of ionic cross-links due to intermolecular ion–ion interactions between pyridinium cations and sulfonate anions, which arose from proton transfer from sulfonic acid groups to pyridine groups upon blending. MDSC detected only one Tg for the SPS/SVP blends, indicating that the blends were unclustered. However, after annealing the blends at 150 °C for 24 h, two Tgʹs were detected, reflecting microphase separation (formation of a cluster phase and a matrix phase) due to aggregation of ionic groups during annealing.