The tensile properties of poly(ethylene oxide)-based segmented block copolymers in the dry and wet state

The tensile properties of poly(ethylene oxide)-based segmented block copolymers were studied in the dry and wet state. The hard segments were made up of monodisperse crystallisable tetra-amide segments (T6T6T) comprising terephthalate (T) and hexamethylenediamine (6) groups. The length of the segments making up the soft phase was varied from 600 to 10,000 g/mol. The water absorption of the PEO-based copolymers was found to increase exponentially with the PEO concentration. The modulus and yield strength decreased with water absorption and this effect seemed to be mainly the result of a lowering hard segment content caused by their swelling with water. Upon wetting, the copolymers demonstrated an increased yield strain. Furthermore, the ultimate properties were sensitive to the hard segment content, the molecular weight of the copolymer and whether or not strain-hardening could take place. Upon wetting, the fracture stresses decreased whereas the fracture strains increased. The true fracture stresses of the wet samples were as high as those of the dry samples for reasonable amounts of absorbed water.