Polyurethane electrostriction was investigated by measuring the tensile electromechanical coupling coefficients of structurally different materials. True values of the strain coefficients M-3311, M-3322, and M-3333 were obtained for four types of polymer: one commercial polyurethane (DOW 2103-80 AE) and three polyurethanes synthesized at the Naval Surface Warfare Center, including two phase-separated (PS) materials with molecular weights of 1000 and 2000 and one phase-mixed (PM) material with a molecular weight of 2000. Measurements were performed at 2 kHz under a bias field of 4 MV/m at room temperature. Measured values of M-3333 ranged from -9.4 x 10(-18) to -74.6 x 10(-18) m(2)/V-2, with the PM material exhibiting the largest coefficient. The electrostatic interaction (Maxwell stress) did not account for more than 15% of the total electromechanical activity in any of the materials. Furthermore, at the macroscopic level, an empirical relationship was established to predict the values of the electrostrictive coefficients from the dielectric constants and the compliance coefficients of the material. Finally, results indicated that, at the microscopic level, the phenomenon of electrostriction in polyurethanes could be best explained by the presence of charges inside the material (space-charge theory). (C) 2003 Wiley Periodicals, Inc.