Relationship between acoustic properties and structure of polyurethanes

Commercial polyurethanes, although convenient, do not provide close sound-speed or density matches with seawater. Several series of diblock copolymer polyurethanes were prepared in order to study the compositional parameters that determine the acoustic properties of this class of compounds. Compositional changes that principally affect the hardblock part of the structure were shown to exert little influence on sound speed or density. Conversely, an increase in the size or quantity of the softblock causes large decreases in the properties, allowing production of polyurethanes with very closely matched properties. Correlation equations for sound speed, density, and specific acoustic impedance are given as a function of calculated number-average molecular weights of the polyurethane softblock. The essential independence of the sound speed from the Shore hardness suggests that the hardblock composition controls the hardness property whereas acoustic properties are determined by the softblock parameters.