The styrene-isoprene-butadiene terpolymer rubbers (SIBRs) with different molecular weights and monomer ratios were first synthesized by living anionic polymerization method.A series of ABS resins were prepared via bulk polymerization method under the initiation of difunctional initiator modified by the foresaid SIBR tougheners.The molecular structure

morphology and performances of ABS were characterized by typical phase-separating method

SEC

TEM and mechanical testing

respectively.And SEM technique was used for observing the fractured surfaces of specimens after impact in order to study the fracture mechanism.The results show that with increasing the molecular weight of SIBR

the rubber phase size increases and the grafting degree decreases besides gradually obvious phase interface and improved impact properties.Moreover

increasing the styrene content in SIBR could lead to relatively uniform particles

but goes against the impact resistance due to its rigidity.The SIBR with higher molecular weight and lower styrene content restrains the generation and development of cracks to a certain extent

and correspondingly

the ABS displays ductile fracture mode and the fracture mechanisms are mainly abundant crazing

obvious shear yielding and a great many ruptured ligaments.While the SIBR with lower molecular weight and higher styrene content could not efficiently resist the formation and expansion of cracks

ABS is fractured in quasi-ductile modes and matrix plasticization

stripping and stress whitening are the main fracture mechanism.