Long chain branching (LCB) were added to linear polypropylene (PP) using reactive extrusion in the presence of selected polyfunctional monomers (PFMs) and a peroxide of dibenzoyl peroxide (BPO). Fourier Transformed Infrared spectra (FTIR) directly confirmed the grafting reaction occurred during the reactive extrusion process. Various rheological plots including viscosity curve, storage modulus, Cole-Cole plot, and Van-Gurp plots, confirmed that the LCB structure were introduced into modified PPs skeleton after modification. In comparison with linear PP, the branched samples exhibited higher melt strength, lower melt flow index, and the enhancement of crystallization temperature. The LCB level in modified PPs and their melt strength were affected by the type of PFM used and could be controlled by the PFM properties and structure. PFMs with lower boiling points, such as 1, 4-butanediol diacrylate (BDDA), could not produce LCB structure in modified PP skeleton. The shorter molecular chain bifunctional monomers, such as 1,6-hexanediol diacrylate (HDDA), favored the branching reaction if their boiling points were above the highest extrusion temperature. And some polar groups, such as hydroxyl, in the molecule of PFM were harmful to the branching reaction, which might be attributed to the harm of the polarity of groups to the dispersion of PFM in PP matrix. (c) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 116: 2557-2565, 2010