Long-chain branching polypropylene (LCB-PP) was achieved by reactive extrusion in the presence of bifunctional monomer [1,6-hexanediol diarylate (HDDA)] and peroxide of dicumyl peroxide (DCP). Influences of HDDA and DCP concentrations on the branching efficiency were comparatively evaluated. Fourier transformed infrared spectroscopy (FTIR) results indicated that the grafting reaction took place, and HDDA has been grafted on PP skeleton. In comparison with initial PP, some modified samples showed lower melt flow index because of a large number of LCB in their skeleton. Several rheology plots were used to investigate the rheological properties of the initial PP and modified PPs, and the rheological characteristics confirmed the LCB in modified PPs skeleton. DSC results showed that the crystallization temperatures of modified PPs were higher than those of initial PP and degraded PP, suggesting that the modified PPs had long-chain branched structure. The contrastive investigation in the rheology of modified PPS suggested that proper concentrations of HDDA and DCP were more beneficial to producing LCB during reactive extrusion. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 113: 2126-2135, 2009