Long chain branching (LCB) of polylactic acid (PLA) was successfully prepared by melt radicals reaction with pentaerythritol triacrylate (PETA) and bis (1-methyl-1-phenylethyl) peroxide (DCP). The topological structure of the LCB was investigated by rheology and branch-on-branch (BOB) model was used to estimate the exact chain structures of the products, where comb-like LCB structures were generated due to the complex coupling between different macro-radicals. LCB structure was found to affect the crystallization of PLA products. In the temperature range of 110130 degrees C, the crystallization rate parameter (k) was improved sharply and the half crystallization time was decreased significantly after the grafting of PETA, which was ascribed to the enhanced hydrogen bonding in PETA-grafted long chain branching PLA. By comparing with the LCB PLA made from chain extension using multifunctional monomer, it shows that the crystallization becomes slower in a highly branched material with extremely long relaxation time if the effect of hydrogen bonding is similar. (c) 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013