A series of polyurethane/vinyl ester resin simultaneous and gradient interpenetrating polymer networks (PU/VER IPN and gradient IPN), cured at room temperature, were synthesized by introducing acrylic esters as VER's comonomers. The effects of thermodynamic factor, kinetic factor, component ratio and gradient techniques on their damping properties were studied by DMA. It was found that the damping properties of general PU/VER (St) IPN with styrene (St) as VER's comonomer are improved by introducing acrylic esters instead of St. When the relative polymerization rates of the networks are close, 80:20, 70:30 and 60:40 PU/VER (BMA) IPNs with butyl methacrylate (BMA) as VER's comonomer have excellent damping properties. The gradient IPN with better damping properties than simultaneous IPNs was obtained by adjusting the gradient techniques. The tan 8 values of the gradient IPN with the time interval of 3 h and the component ratios of 50:50-60:40-70:30 are higher than 0.3 from -57 degreesC to higher than 90 degreesC, and its tan 6 values are higher than 0.5 from -36 to 54degreesC. The results of EDX revealed that the gradient structure is formed in transition regions of gradient IPN. The results detected by TEM and AFM showed that the phase ranges of PU/VER (BMA) IPNs and gradient IPN obtained are both in nanometer scale. Furthermore, the relationship of microstructure and damping properties was studied. (C) 2004 Elsevier B.V. All rights reserved.