| As a polymer alloy, impact polypropylene copolymer (IPC) is prepared by two step polymerization. Due to having good strength and impact toughness, IPC has been widely used in many industries. The diversity of the arrangement of propylene and ethylene units during the copolymerization step leads to an extremely complex composition of IPC. In addition, as a multi-component and multi-phase material, the IPC melt exhibits the characteristic rheological behavior. Considering that the performances of IPC strongly depend on its microstructure and composition, and the rheological behavior can reflect the processing property of the IPC, the study on the structure and rheological behaviors are necessary to optimize its performances and develop the optimal processing theory. In this dissertation, the chain structure, compatibility and morphology of IPC were studied and a phase model of IPC was put forward. The dynamic rheological behavior of IPC and its fractions were discussed. Furthermore, an IPC/HDPE (high density polyethylene) laminate was prepared by hot press and the high weld strength between IPC and HDPE was studied.The IPC was fractionated into three fractions (F50, F100 and F125) by means of temperature-gradient extraction fractionation. The thermal behavior of these three fractions was studied by modulated differential scanning calorimeter (MDSC) and dynamic mechanical analysis (DMA). The results show that these three fractions correspond to three main components of IPC, i.e. ethylene-propylene random copolymer (EPR), ethylene-propylene block copolymer (EbP) and propylene homopolymer (HPP), separately. It was also found that both IPC and EbP fraction (F100) present three glass transition peaks, and the glass transition temperature of EPR in IPC sample is remarkably lower than that of pure EPR fraction (F50) due to the existence of EbP component with special structure in IPC. Furthermore, by using successive self-annealing (SSA) technique, cocrystallization occurring between the polypropylene chains in EbP fraction and in HPP fraction was found for solution-mixed EbP/HPP blends, and it is believed that there exists a dilute effect of EPR on the crystallization of EbP fraction for the solution-mixed EPR/EbP blends. Accordingly, it can be inferred that EbP fraction has good compatibility with both EPR and HPP fractions, and it confirms that the compatibilization effect of EbP fraction in IPC is good.Based on electronic microscopy observation and results of chain structure analysis, a modified multi-layer core-shell phase structure model was put forward for IPC. In this model, the HPP component and EPR component were believed to be the matrix and the main dispersed phase respectively, and depending on its chain structure, the EbP component could form the core, the layer or the bridges connecting the core and EbP layer. It was found that even this multi-layer core-shell structure is completely destroyed, it can be rebuilt by thermal treatment, with a way analogous to self-assembly process. This indicates that the multi-layer core-shell structure is stable in thermodynamic to some extent.The dynamic rheological behavior of the melts of IPC and its three fractions were examined. The results shows that the dynamic storage modulus (G') of IPC exhibits "pseudo solid-like" phenomenon behavior at low frequency (ω). This result indicates that the IPC melt is endowed with a characteristic of heterogeneous phase. The differences in the G'and complex viscosity (η*) among the fractions of IPC appear dramatic, which are probably induced by the large variance of the molecular weight and the length of the molecular chains among the fractions. The EPR and HPP fractions present the fine linear viscoelasticity, implying that these fractions are homogeneous system. Moreover, the dynamic rheological behavior of the EbP exhibits "pseudo solid-like" behavior at lowω, meaning that this fraction is a heterogeneous system. On the other hand, the'second plateau'can be observed in low co region for the HPP/EPR blends when the proportion of the EPR is the same as the proportion of EPR in IPC, suggesting that the "second plateau" in IPC results from the phase-separation between HPP and EPR, and the existence of EbP is not a key factor in the generation of "second plateau" for IPC.The IPC/HDPE laminate was prepared and the peeling test result showed that the welded joint strength of the laminate is high. The thermal analysis results indicated that there exist some interactions between IPC and HDPE, and the crystallizable PE component in IPC could affect the crystallization of HDPE. On the basis of the morphological results of IPC/HDPE blends, it is suggested that HDPE tends to stay with the PE-rich EbP chains in IPC to form the dispersed phase, indicating the good compatibility between HDPE and EbP components of IPC.
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