The reaction of melt poly(ethylene-alpha-octene) (POE) initiated by dicumyl peroxide (DCP) was studied at elevated temperature in both oscillatory and transient shear flow fields. In oscillatory shear flow, the storage modulus evolution was monitored by parallel plate rheometer with certain oscillatory frequencies and different strains, which were chosen to represent different flow fields. Our results indicated that at low frequencies (0.1 and 0.4 Hz) the dominant reaction was coupling with small strain amplitudes within the linear viscoelastic regime. However, the degradation, which was caused by beta-scission of tertiary carbon macromolecular radicals, also occurred when large strains were applied, which were out of the linear viscoelastic regime. The threshold strain of degradation was only 8% at 1.5 Hz, still within the linear viscoelastic regime. The mechanisms of how the frequency and strain affected the degradation were different. On the other hand, in transient shear flow the degradation could hardly take place when the shear rate was lower than the critical value of 0.0025 s(-1). Moreover, the larger the shear rate, the more distinct was the degradation. (c) 2006 Elsevier Ltd. All rights reserved.