Polyurethanes are a class of polymers that exhibit a wide range of mechanical properties. Among various polyurethanes, thermoplastic polyurethane elastomers (TPUs) are frequently used in underwater applications such as encapsulants for undersea sonar devices, electric wires, and communication lines.[1- 5] TPUs used for sonar encapsulants must satisfy particularly stringent requirements. Sonar devices are dragged behind submarines or surface ships, and the encapsulant is filled with a paraffin oil to protect against the ingress of seawater. To adapt to operating conditions, TPUs used as sonar encapsulants should possess a low swelling ratio in seawater and paraffin oil and be able to withstand hydrolysis and prolonged extensional stress without significant deterioration of their properties.
