A grafting monomer (p-(3-butenyl)styrene, BS)) containing two carbon carbon double-bonds with different reactivity was used in melt radical reaction to prepare long chain branched polypropylene (LCB-PP). High-temperature size-exclusion (HT-SEC) coupled with triple detectors, rheometer and NMR were used to characterize the microstructure of the resultant LCB-PP. BS showed double functions in mediating radical reaction, i.e. stabilizing macroradicals and promoting branching reaction. Compared to styrene and divinylbenzene, using BS as a grafting monomer led to the formation of more uniformly distributed LCB structure on the PP backbone. Thus the resultant sample showed strain hardening in extensional flow and had high melt strength. (C) 2011 Elsevier Ltd. All rights reserved.