The degradation and in situ reaction with polystyrene (PS) of polyolefin elastomers in the melt state induced through high intensity ultrasonic wave were investigated. The effects of initial molecular weight of polyolefin elastomers, irradiation time, ultrasonic intensity, as well as reaction temperature on the ultrasonic degradation of polyolefin elastomers melt were studied using a "static" ultrasonic vibration system. The results show that the degradation occurs mostly at the tip of the ultrasonic probe, and little or no degradation was observed at the distance of 5 mm or greater from the tip of the probe. The intrinsic viscosity [eta] of polyolefin elastomers near the tip of ultrasound probe significantly decreases with irradiation time in the first 100 s and tends toward a limiting value for all samples. The degradation rates increased with an increase in ultrasonic intensity and decrease in reaction temperature. The ultrasonic degradation kinetics of polyolefin elastomers in melt state follows the equation: [eta](t) = [eta](infinity) + Ae(-kt). The fitting results by this equation accord well with the experimental data. The feasible ultrasonic degradation mechanism is proposed based on the viscoelastic characteristic of polymer melt. FTIR analysis confirms that the copolymer forms under ultrasonic irradiation for PS/POE mixtures and in situ reaction of polymer in melt state can be induced by ultrasonic irradiation. (c) 2007 Wiley Periodicals, Inc.