In order to control the length of branched chains on polypropylene, the effects of melt reactions during preparing long chain branched polypropylene (LCB-PP) via free radical grafting were studied. The LCB structure was confirmed by fourier transform infrared spectroscopy (FTIR), dynamic viscoelastic measurements and thermal analysis. The results showed that TETDS could efficiently control degradation of PP backbone and homopolymerization of multifunctional monomer (1,6-hexanediol diacrylate (HDDA)) in the presence of dibenzoyl peroxide (BPO) during melt grafting. This could also increase in the extent of the LCB structure. The dithiocarbamate radicals which are formed through the reaction between TETDS and active free radicals (carbon centered and alkoxy species) cannot attack PP backbone and are weaker initiator for HDDA. Thus the instantaneous concentration of active free radicals is decreased, and the degradation of PP backbone and the homopolymerization of HDDA can be controlled. Moreover, the dithiocarbamate radicals could react with the PP macroradicals and the acrylic radicals reversibly, which make longer the life time of PP macroradical and increase the reaction probability between macroradicals. It was demonstrated that the results of melt linear viscoelastic measurement together with extensional viscosity can be utilize as a strong tool in determining the extent of chain branching and chain length.