ABSTRACT:The thermal behavior and the miscibility of an in-situ polypropylene blend named polypropylene catalloys (PP-cats) were investigated by using modulated differential scanning calorimeter (MDSC). It is found that all PP-cats samples present two glass transitions, one of which is ascribed to the ethylene-propylene random copolymer (EPR), and the other, to isotactic polypropylene (PP). However, no glass transition of ethylene-propylene block copolymer (E-b-P) responsible for a third component in PP-cats could be found. With the increase of EPR, the glass transition temperatures responding to PP and EPR components, T g , PP and T g , EPR , shift to low temperature, because of the enhancement of the interaction between PP and EPR component and the increase of ethylene content in EPR, respectively. Furthermore, the difference between T g , PP and T g , EPR remarkably decreases with the increase of the total ethylene content in PP-cats, which indicates that the miscibility of PP-cats is strongly dependent on the composition. Comparing the T g , PP and T g , EPR with T g of fractionated PP and EPR, we ascribe the T g change of PP fraction to the increase of EPR content; while that of EPR, to the increase of ethylene content in EPR. These experimental results suggest that the existence of E-b-P plays an important role in improving the miscibility between propylene homopolymer and EPR in PP-cats.

The effects of preparation method, composition, and thermal condition on formation of β‐iPP in isotactic polypropylene/ethylene–propylene rubber (iPP/EPR) blends were studied using modulated differential scanning calorimeter (MDSC), wide angle X‐ray diffraction (WAXD), and phase contrast microscopy (PCM). It was found that the α‐iPP and β‐iPP can simultaneity form in the melt‐blended samples, whereas only α‐iPP exists in the solution‐blended samples. The results show that the formation of β‐iPP in the melt‐blended samples is related to the crystallization temperature and the β‐iPP generally diminishes and finally vanishes when the crystallization temperature moves far from 125 °C. The phenomena that the lower critical temperature of β‐iPP in iPP/EPR obviously increases to 114 °C and the upper critical temperature decreases to 134 °C indicate the narrowing of temperature interval, facilitating the formation of β‐iPP in iPP/EPR. Furthermore, it was found that the amount of β‐iPP in melt‐blended iPP/EPR samples is dependent on the composition and the maximum amount of β‐iPP formed when the composition of iPP/EPR blends is 85:15 in weight. The results through examining the effect of annealing for iPP/EPR samples at melt state indicate that this annealing may eliminate the susceptibility to β‐crystallization of iPP. However, only α‐iPP can be observed in solution‐blended samples subjected to annealing for different time. The PCM images demonstrate that an obvious phase‐separation happens in both melt‐blended and solution‐blended iPP/EPR samples, implying that compared with the disperse degree of EPR in iPP, the preparation method plays a dominant role in formation of β‐iPP. It is suggested that the origin of formation of β‐iPP results from the thermomechanical history of the EPR component in iPP/EPR. © 2007 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 45: 1704–1712, 2007

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