The composition and structure of polymer largely determine the properties of its final products.As a novel polymer material,the composition,structure,and properties of the isotactic polypropylene/polybutene-1 in-reactor alloy (iPP/iPB alloy) synthesized by sequential two-stage polymerization with Ziegler-Natta catalyst were correlated for the first time in this work.The iPP/iPB alloy was fractionated by temperature rising elution fractionation (TREF) in a broad temperature ranged from-30 ℃ to 140 ℃,and the chain microstructures and sequence distributions of isolated fractions were analyzed by DSC,GPC,13C-NMR,and FTIR.The iPP/iPB alloy was composed of five components,namely high isotactic PB (iPB,85.8 wt%),medium isotactic PB (mPB,5.1 wt%),poly((butene-1)-block-propylene) copolymers (PB-b-PP,4.1 wt%) which contained PB and PP blocks with different lengths according to the isolation temperature,isotactic PP (iPP,2.7 wt%),and atactic PB (aPB,2.3 wt%).Compared to other commercial pipe materials,the iPP/iPB alloy presented outstanding thermal creep resistance and gas permeability resistance,high strength and low deformation at high temperature,and appropriate flexural strength.The roles of PP and PB-b-PP components in the alloy were interpreted.This work is expected to elucidate the potential application of iPP/iPB alloy as pipe materials and provide solutions for the design and synthesis of high performance pipe materials.