Ethylene-propylene Random Copolymer Research Articles

Processing effects on crystal morphology and application performance of blown films from propylene-ethylene random copolymers

Processing effects on crystal morphology and application performance of blown films from propylene-ethylene random copolymers

Polyolefin Blends with Selectively Crosslinked Disperse Phase Based on Silane-Modified Polyethylene.

Polypropylene-based multiphase compositions with a disperse elastomer phase provide superior impact strength. Making this property indifferent to processing steps requires stabilization of the morphology of these materials. Various approaches have been tested over time, each of which shows limitations in terms of performance or applicability. Using polyethylene (PE) homo- and copolymers capable of silane-based crosslinking as modifiers was explored in the present study, which allows decoupling of the mixing and crosslinking processes. Commercial silane-copolymerized low-density PE (LD-PEX) from a high-pressure process and silane-grafted high-density PE (HD-PEX) were studied as impact modifiers for different types of PP copolymers, including non-modified reference PE grades, LDPE and HDPE. Blends based on ethylene-propylene random copolymers (PPR) and based on impact- (PPI) and random-impact (PPRI) copolymers show improvements of the stiffness-impact balance; however, to different degrees. While the absolute softest and most ductile compositions are achieved with the already soft PPRI copolymer base, the strongest relative effects are found for the PPR based blends. Modifiers with lower density are clearly superior in the toughening effect, with the LD-PEX including acrylate as second comonomer sticking out due to its glass transition around -40 °C. The impact strength improvement found in most compositions (except at very high content) results, however, not from the expected phase stabilization. For comparable systems, particle sizes are normally higher with crosslinking, probably because the process already starts during mixing. Thermoplastic processability could be retained in all cases, but the drop in melt flow rate limits the practical applicability of such systems.

Furan as Impurity in Green Ethylene and Its Effects on the Productivity of Random Ethylene-Propylene Copolymer Synthesis and Its Thermal and Mechanical Properties.

The presence of impurities such as H2S, thiols, ketones, and permanent gases in propylene of fossil origin and their use in the polypropylene production process affect the efficiency of the synthesis and the mechanical properties of the polymer and generate millions of losses worldwide. This creates an urgent need to know the families of inhibitors and their concentration levels. This article uses ethylene green to synthesize an ethylene-propylene copolymer. It describes the impact of trace impurities of furan in ethylene green and how this furan influences the loss of properties such as thermal and mechanical properties of the random copolymer. For the development of the investigation, 12 runs were carried out, each in triplicate. The results show an evident influence of furan on the productivity of the Ziegler-Natta catalyst (ZN); productivity losses of 10, 20, and 41% were obtained for the copolymers synthesized with ethylene rich in 6, 12, and 25 ppm of furan, respectively. PP0 (without furan) did not present losses. Likewise, as the concentration of furan increased, it was observed that the melt flow index (MFI), thermal (TGA), and mechanical properties (tensile, bending, and impact) decreased significantly. Therefore, it can be affirmed that furan should be a substance to be controlled in the purification processes of green ethylene.

Morphology and physical properties of composites based on high-density polyethylene/propylene-ethylene random copolymers blends and carbon black

High-density polyethylene (HDPE) composites containing propylene-ethylene random copolymers (PEC) elastomer and carbon black (CB) were prepared by melt blending in an effort to obtain excellent balance of properties. HDPE matrix and PEC elastomer were immiscible, and CB fillers were selectively located in HDPE matrix. The introduction of CB fillers into the HDPE/PEC blend significantly improved the viscoelasticity of the composite melts. Percolation network of CB particles was formed at CB content of 5 wt%, which consequently largely improved the conductivity of composites, and the surface resistance decreased to 106 Ω (square)−1, equal to the antistatic range. DSC results suggested that CB with a content more than 5 wt% showed nucleation effect, improving the degree of crystallinity of HDPE. Moreover, the incorporation of CB improved stiffness of composites, and decreased ductility compare with HDPE/PEC blend. The combination of adjustable conductivity and mechanical properties, as well as improved melt viscoelasticity wold further broaden the application fields of HDPE based composites.

Ethylene Comonomer-Directed Epitaxial Nucleation and Growth of β-Nucleated Isotactic Polypropylene

We present a molecular-level investigation of the epitaxial crystallization of β-nucleated isotactic polypropylene associated with the minor and local topographic modification at the interface, i.e., the inclusion of an ethylene comonomer. The experimental results show that the relative fraction of β-crystal (Kβ) decreases progressively with increasing the amount of ethylene comonomer, which originates from a simultaneous reduction in the β-nucleation ability of a β-nucleating agent (N,N′-dicyclohexylterephthalamide, DCHT) toward propylene–ethylene random copolymers (PERs) and the growth rate of the β-crystal relative to the α-crystal. With the aid of molecular mechanics simulation, we demonstrate that such a topographic modification weakens the intermolecular interactions at the nucleation and growth interfaces, thereby modifying the epitaxial nucleation of the β-crystal and the growth kinetics of β- and α-crystals. The study reveals that the polymorph selection of the PERs/DCHT system is not solely determined by the lattice match but also profoundly influenced by the topography characteristics dependence of molecular interaction at the crystalline interfaces. Our fundamental insight could have important implications in the control of the polymorphism of polymers through the careful design of the topography of the nucleation and growth interfaces.

Morphology, rheological, thermal, and mechanical properties of high-density polyethylene toughened by propylene-ethylene random copolymers

Morphology, rheological, thermal, and mechanical properties of high-density polyethylene toughened by propylene-ethylene random copolymers

An experimentally validated model for quiescent multiphase primary and secondary crystallization phenomena in PP with low content of ethylene comonomer

While crystallization behavior of isotactic polypropylene homopolymers had been subject to a wide range of experimental and modeling studies, this is not the case for propylene-ethylene random copolymers (PPR). This class of polymers offers up to now significant challenges, both from an experimental as well as a modeling perspective. The ethylene incorporation in the propylene chains, as well as the distribution of this comonomer, has a marked effect on the crystallization kinetics. Moreover, the presence of these defects causes a clear separation between primary crystallization (i.e. space filling) and subsequent secondary crystallization (increase of crystallinity in filled space) within the spherulitic skeletons, particularly subsequent at high primary crystallization temperatures. In this work, the underlying mechanism is first quantified by means of a combination of in-situ WAXD and SAXS experiments, as well as ex-situ WAXD experiments and calorimetric measurements. Based on these experiments an extended model framework is presented, capable of predicting multiphase non-isothermal crystallization kinetics as well as the final crystallinity as a function of the applied thermal conditions relevant for processing. The chemical composition distribution (CCD) of the ethylene comonomer serves as critical input to parameterize the model. Optical microscopy- and DSC experiments are used for parameterization of the primary crystallization model. The model developed in this study is, in principle, applicable to all polypropylenes, ranging from homo-polymers to random copolymers with variable comonomer content and/or CCD but, so far, only applied and validated on one PPR. To validate the model and the parameters for a given PPR, several non-isothermal and isothermal experiments (the latter followed by subsequent cooling) are conducted over a wide range of crystallization temperatures and cooling rates. The good match between experiments and model predictions demonstrates the power of the newly developed framework. The final crystallinity, the amount of α - and γ -phase, and the ratio between primary and secondary crystallization can be predicted as a function of the time-temperature history. To the best knowledge of the authors, it is the first time that such a direct connection with the CCD is incorporated in a crystallization model. Consequently, the model offers a new tool to bridge the gap between chemical structure and resulting product properties, which now has come one step closer for PPR systems. • Isothermal and cooling experiments reveal primary and secondary crystallization behavior of PPR. • Primary crystallization is modeled via formation of α-skeletons, in which γ-phase co-crystallizes. • Incorporated multi-phase secondary crystallization to predict final phase composition. • Final crystallinity from the introduction of a crystallizable fraction and kinetic maximum. • Direct link between chemical composition distribution and crystallization kinetics.

Enhancing electrical properties of impact polypropylene copolymer for eco-friendly power cable insulation by manipulating the multiphase structure through molten-state annealing

Composite insulating materials with high electrical properties are integral for high voltage power cable. In this paper, we achieved significant increases by about 17% and 30% in breakdown strength and charge injecting transition field of impact polypropylene copolymer (IPC), a promising composite for power cable insulation, through 60 min molten-state annealing (MSA). To unravel the influencing mechanism of MSA on electrical properties, the multiphase structure evolution were investigated. Results showed that ethylene-propylene random copolymer (EPR) was separated from matrix with ongoing MSA. Meanwhile, two melting peaks were found in DSC curves. The one at lower temperature was raised from 142.2 °C to 144.6 °C after 60 min MSA, while the higher one remained unchanged, indicating the increase in thickness of partial lamellas, which was proved to be the reason for the increased deep trap level from 1.01 eV to 1.05 eV. Under 50 Hz AC electric field, electro-hole recombination was proposed to be the main origins of high-energy electrons, rather than acceleration under electric field. The greater the energy level of the deep trap, the smaller the energy released by recombination, resulting in reduced probability of collision ionization and thus increased breakdown strength. This work provides a new comprehending into the electrical breakdown and its enhancement of IPC eco-friendly power cable insulation.

Choosing an Effective Compatibilizer for a Virgin HDPE Rich-HDPE/PP Model Blend.

The most widely used commodity polymers in the rigid packaging industry are polypropylene (PP) and high-density polyethylene (HDPE). For example, blow molding grade of HDPE as a bottle and injection molding grade of PP as a cap are often used to produce detergent bottles. Therefore, the recycled HDPE bottles from post-consumer waste include PP as a contaminant originated from PP bottle caps. To simulate mechanical recycling of bottle waste, the mechanical properties of HDPE-rich-HDPE/PP virgin model blend were studied. For compatibilization, ethylene-based olefin block copolymer, propylene-based olefin block copolymer, ethylene propylene random copolymer, and styrene-butadiene-styrene triblock copolymer were chosen as potential compatibilizer candidates. Contact angle measurements, morphological analysis, adhesion tests of compatibilizer candidates to polymer blend components and the tensile as well as tensile impact properties of the ternary blends were studied. It was found that the ethylene-based olefin block copolymer was the most effective compatibilizer resulting in a return of mechanical properties to those of neat vHDPE due to its ability to encapsulate dispersed vPP particles in a vHDPE matrix (core-shell morphology) and the best adhesion to polymer blend components.

Structural evolution of mesomorphic propylene–1‐butene random copolymer during heating process

AbstractThe study of the transition of mesophase to α‐crystal (meso–α transition) is of great significance for understanding the crystallization, morphology as well as processability of polypropylene materials. The structural evolution of mesomorphic isotactic propylene–1‐butene (iPPBu) random copolymer during the continuous heating process was investigated using in situ Fourier transform infrared spectroscopy, differential scanning calorimetry, wide‐angle X‐ray diffraction and dynamic mechanical analysis. The presence of the butene comonomer influences the meso–α transition behavior. Compared with the mesomorphic iPP homopolymer, the presence of butene comonomer reduces both onset temperature (Tonset) and end temperature (Tend) of the meso–α transition, and narrows the transition temperature range. The content of the 31 helical sequence with 12 monomers remains invariant during the meso–α transition, differing from that of mesomorphic iPP homopolymer. Similar to mesomorphic iPP homopolymer, the 31 helical sequence with monomer number n ≤ 12 is found to exist in the rigid amorphous fraction of iPPBu, but is different from that of a mesomorphic propylene–ethylene random copolymer. In the meso–α transition (from 60 to 100 °C), the redshift of the peak position of the band at ca 841 cm−1 provides new information for the approaching of adjacent stems at the molecular level. Moreover, a new peak at around Tend is found in the tan(δ)–T plot, and is correlated with the meso–α transition. The activation energy of the meso–α transition of mesomorphic iPPBu is 32.5 kJ mol−1, which is slightly lower than that of mesomorphic iPP homopolymer. This work sheds new light on further understanding of the meso–α transition mechanism of iPPBu copolymer at the molecular level and elucidates the effect of butene comonomer on the meso–α transition. © 2021 Society of Industrial Chemistry.

Revisiting the Mechanism of the Meso-to-α Transition of Isotactic Polypropylene and Ethylene–Propylene Random Copolymers

In this work, we have conducted in situ simultaneous small- and wide-angle X-ray scattering and Raman spectroscopy experiments to investigate the fundamental differences in the mechanism of the mesomorphic to α phase transition of the isotactic polypropylene homopolymer and the random ethylene–propylene copolymer. Via quantitative analysis of the results coming from the three techniques, we found that in the homopolymer, chain interlock and chain extension occur during the transition. However, these processes are not necessary for the transition to occur. Indeed, the presence of randomly distributed ethylene co-units hinders the chain interlock process in the early stages of the phase transition (T > 60 °C) and suppresses the chain elongation process at the later stages (T > 90 °C). Consequently, the mesomorphic to α-phase transition in the random copolymer occurs with inclusion of the ethylene co-units inside the crystal lattice, causing increased lateral interchain distance and larger crystalline sizes. Our results show how differences exist in the way solid phase transitions occur at the molecular scale when co-monomers are included into the macromolecular chains, leading to a better understanding of the thermal behavior of semi-crystalline polymers.

Temperature dependency of cavitation in impact copolymer polypropylene during stretching

Cavitation in the impact copolymer polypropylene (ICP) and its corresponding homo-isotactic polypropylene (homo-iPP) during stretching was investigated using ultra-small angle X-ray scattering technique. Different from the iPP showing a suppressed cavitation around yielding at high deformation temperature (Td), the ICP presented a more intensive cavitation at elevated Td. This unusual Td dependency of cavitation around yielding observed in ICP was suggested to be caused by the changes of the stability of the rubber particles dispersed in iPP matrix. The rubber particles exhibit a multi-phase core-shell structure which contains crystallizable polyethylene segments in the core layer, the amorphous polymer of ethylene-propylene random copolymer in the inner shell layer, and the crystallizable polypropylene segments in the outer shell layer. The softening and melting from the inner shell to the core and the outer shell took place as the Td increased. It can be envisaged that the fraction of unstable regions inside the rubber particles and the debonding between the iPP matrix and the dispersed phase gradually increased providing more nucleation sites for cavities at high Td, a more intensive cavitation was thus observed.

New Insights into Crystallization of Heterophasic Isotactic Polypropylene by Fast Scanning Chip Calorimetry.

The crystallization kinetics of metallocene-catalyzed heterophasic isotactic polypropylene composed of a matrix of isotactic polypropylene (iPP) and rubbery particles made of random ethylene–propylene copolymers (EPC), often denoted as heterophasic iPP copolymers, was analyzed as a function of the cooling rate and supercooling in nonisothermal and isothermal crystallization experiments, respectively. Fast scanning chip calorimetry (FSC) allowed assessing crystallization at processing-relevant conditions, and variation of the content (0–39 wt %) and composition (0–35 wt % propylene counits) of the EPC particles revealed qualitatively new insight about mechanisms of heterogeneous crystal nucleation. For neat iPP homopolymer, the characteristic bimodal temperature dependence of the crystallization rate due to predominance of heterogeneous and homogeneous crystal nucleation at high and low temperatures, respectively, is reconfirmed. At high temperatures, in heterophasic iPP, the here studied ethylene-(C2)-rich EPC particles accelerate crystallization of the iPP-matrix, with the acceleration or nucleation efficacy correlating with the EPC-particle content. The crystallization time reduces by more than half in presence of 39 wt % EPC particles. An additional nucleating effect of the EPC particles on iPP-matrix crystallization is detected after their crystallization, suggesting that liquid/rubbery particles are less effective than solid/semicrystalline particles in affecting crystallization of the surrounding iPP-matrix. At low temperature, homogeneous crystal nucleation in the iPP-matrix outpaces all heterogeneous nucleation effects, and the matrix-crystallization rate is independent of the sample composition. The obtained results lead to the conclusion that the crystallization kinetics of iPP can be affected significantly by the content and composition of EPC particles, even towards superfast crystallizing iPP grades.

Insulative ethylene-propylene copolymer-nanostructured polypropylene for high-voltage cable insulation applications

Worldwide, various efforts to replace crosslinked-polyethylene (XLPE) as an insulation layer in the cable industry, is becoming increasingly popular for improved recycling of polymer waste. Polypropylene (PP) has been proposed as a representative candidate because of its excellent thermomechanical and electrical performances. However, overcoming the mechanical limitations of intrinsic rigidity is required for cable applications. Herein, PP-based insulating materials were prepared via melt-blending with rubbery ethylene-1-octene copolymer (EOC), followed by mixing an ethylene-propylene random copolymer (rPP) as a surfactant for high-voltage power cable applications. Simple melt-blending of rPP formed a core-shell nanostructure composed of EOC/rPP and a fine dispersion of macron-sized EOC domains. The nanostructured PP ternary blends exhibited multiple advantages in terms of thermal stability, mechanical properties, dielectric performances, and long-term stability compared to the existing XLPE. This study provides a straightforward, rational design of environmental insulation materials for high voltage power cable applications.

Chain microstructure of two highly impact polypropylene resins with good balance between stiffness and toughness

For highly impact polypropylene (HIPP), a good balance between stiffness and toughness has attracted much attention from both industrial and academic research. Herein, two HIPP resins (A and B) with different ethylene contents and impact resistances especially at low temperatures are investigated. Their chain microstructure is studied by combining preparative temperature rising elution fractionation (P-TREF) with multiple characterization techniques such as high-temperature gel permeation chromatography (HT-GPC), Fourier transform infrared (FTIR) spectroscopy, 13C nuclear magnetic resonance (13C NMR), wide-angle X-ray diffraction (WAXD), differential scanning calorimetry (DSC), rheometer, and thermal fractionation. Both samples are mainly composed of four portions: amorphous ethylene−propylene random copolymer (EPR), ethylene−propylene (EP) segmented and blocky copolymer, and isotactic polypropylene homopolymer. Sample A contains ~30 wt% EPR fractions eluted at 35 °C, ~9 wt% EP segmented and blocky copolymers eluted at 80–100 °C, and ~19 wt% highly isotactic polypropylene fractions eluted at 125–140 °C, which are higher than the contents of corresponding fractions in sample B. Moreover, most fractions of sample A have higher molecular weights than the corresponding fractions of sample B. The contribution of different components to stiffness and toughness is also discussed. The excellent impact resistance of sample A is demonstrated from the perspective of chain microstructure.

Progress in advanced catalyst and their use in ethylene/propylene copolymerization

Ethylene-propylene rubber (EPR) and ethylene-propylene-diene rubber (EPDM) have important market shares of the industry due to their excellent resistance toward heat, oxidation, weather, and other chemicals. EPR and EPDM have been synthesized by ethylene/propylene copolymerization and ethylene/propylene/nonconjugated diene copolymerization, respectively, employing Ziegler-Natta, metallocene and metal complex catalysts. Catalyst plays important roles in the copolymerization of ethylene and propylene. The progress of Ziegler-Natta, metallocene and metal complex catalysts and their use in ethylene/propylene copolymerization were reviewed. The characteristics and application in the industry of these advanced catalysts were introduced. The effects of metals and their valence in catalysts, chemical structure of ligands, cocatalysts and additives on the catalytic activity, composition, molecular weight, molecular weight distribution and sequence of the resulting ethylene-propylene copolymer were discussed. Vanadium based Ziegler-Natta catalyst is still promising in ethylene/propylene copolymerization. The open active site of vanadium catalyst results in random ethylene-propylene copolymers, which prevent the formation of long crystallized ethylene sequences. Meanwhile, the good solubility in alkanes and low cost of vanadium-based Ziegler-Natta catalyst are benefit for the application for the production of ethylene-propylene rubber in industry. About 70% of the commercial E/P copolymers are conducted by using vanadium based Ziegler-Natta catalysts. However, the unstable active centers brought low activity and the catalyst residues should be removed from the polymer product after deactivation. In order to improve the catalytic activity of vanadium-based Ziegler-Natta catalyst, the additives including electron donor and promoter are usually introduced to the catalytic system. The reactivity ratio of the monomer and the microstructure of the resulting ethylene-propylene copolymer could be adjusted by the additives. Metallocene catalyst, as a single-site catalyst, becomes a promising choice for ethylene/propylene copolymerization because of its high activity, high thermal stability and excellent copolymerization ability. The microstructure of resulting ethylene-propylene copolymer could be controlled by modification of chemical structure of metallocene catalyst. The alternating ethylene-propylene copolymer could be prepared by ethylene/propylene copolymerization using bridged zirconocenes. The half-titanocenes containing monodentate anionic nitrogen ligand exhibit high catalytic activity for ethylene-propylene copolymerization in high reaction temperature. Some of metallocene catalyst such as constrained geometry catalyst and half-titanocene catalyst have been applied in the production of ethylene-propylene rubber. The metal complex catalyst for olefin coordination polymerization and copolymerization have attracted considerable attention. The titanium, zirconium and vanadium complexes exhibit high activity for ethylene/propylene copolymerization and ethylene-propylene copolymers with high and ultra-high molecular weight could be prepared by using these complex catalysts. Living copolymerization of ethylene and propylene is achieved by using titanium complex containing phenoxy-imine ligands. The application in industry for the preparation of ethylene-propylene rubber using complex catalyst is still on the way. In conclusion, the high catalytic activity and propylene incorporation in ethylene/propylene copolymerization could be obtained by using advanced catalysts. In addition, the molecular weight, molecular weight distribution, sequence and topological structure could be controlled by advanced catalysts. Therefore, ethylene-propylene rubber with high performance could be prepared by ethylene-propylene copolymerization using advanced catalysts.

Morphology and properties in the binary blends of polypropylene and propylene–ethylene random copolymers

Propylene-based random copolymers copolymerized by propylene and ethylene (PEC) with low degree of crystallinity were used for the modification of isotactic polypropylene (PP) in this work. The phase morphology, miscibility, mechanical properties and rheological properties of the PP/PEC blends were systematically investigated. Dynamic mechanical analysis (DMA) and differential scanning calorimeter (DSC) results verified that the blends were partial miscibility. This may be due to the fact that the PP segments from PEC chains are incorporated into crystal lattice of neat PP, and they together act as a matrix of the PP/PEC blends. The rest of the PEC chains serve as the dispersed phase. The segments from the PEC chains incorporated into pure PP play the role of compatibilizer between the PP matrix and the dispersed phase, which make the dispersed phase to be uniformly dispersed in the PP matrix, resulting in an increase in impact strength from 5 kJ/m2 of neat PP to 40 kJ/m2 of blend with 20 wt% PEC. In addition, the viscosity and modulus of the blends were lower than that of pure PP due to the dilution of PEC in the molten state.

Mechanism of Significant Improvement of Large Strain Elasticity in Soft Propylene–Ethylene Random Copolymer via Blending with Hard Propylene–Ethylene Coplymer

The deformation behavior of propylene–ethylene copolymers with 23 mol % of ethylene (iPPcoE23) and its blend (90/10 w/w) (iPPcoE23b) with propylene–ethylene copolymer (6 mol % ethylene) (iPPcoE6) at room temperature was studied by in situ small-angle X-ray scattering and wide-angle X-ray diffraction techniques. The 10 wt % copolymer with 6 mol % ethylene counits dispersed as small domains in the matrix of iPPcoE23. During stretching, longer and thinner fibrils and better elasticity properties were shown in the blend iPPcoE23b at large strain regime. The higher elasticity for iPPcoE23b at large strain regime was ascribed to the weak ability of strain-induced crystallization due to cocrystallization of the crystallizable long chain sequences of iPPcoE23 with the high crystalline iPPcoE6 during cooling, leaving fewer long crystallizable sequences in the matrix in iPPcoE23b. In addition, the phase-separated domains contributed stronger network modulus in the late stage of stretching compared with that of the ...

Abnormal crystallization behavior of high impact polypropylene under shear

The crystallization of two high impact polypropylenes (HIPP) was investigated under shear flow by online rheo-Raman spectroscopy. Abnormal retardation of crystallization under shear is observed in one HIPP, but the usual shear accelerated crystallization is observed in the other one. Such abnormal phenomenon was understood by thorough investigations on the phase separation behaviors in two HIPPs by scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and rheology. The slowdown of crystallization under shear can be ascribed to the suppression of the interface and fluctuation assisted nucleation under shear, which cannot be compensated by the acceleration effect due to molecular stretching/orientation under shear. The difference between two HIPP comes from the interplay between the suppression and acceleration effect of shear flow, which is determined by the amount of ethylene-propylene segmented copolymer (EPS) and its selective location in isotactic polypropylene (iPP) and ethylene-propylene random copolymer (EPR).

Morphology and properties of PP in-reactor alloys prepared with a MgCl2/TiCl4/diisobutyl phthalate/phosphate tris-methylphenyl ester catalyst system

A series of polypropylene(PP)/poly(ethylene-co-propylene) in-reactor alloys with different ethylene con-tents was prepared through a two-stage polymerization process using a MgCl2/TiCl4/diisobutyl phthalate/phosphate tris-methylphenyl ester catalyst system. The ethylene content, particle shape, fractured surface, and glass-transition temperature(Tg) of the obtained PP in-reactor alloys were characterized by means of nuclear magnetic resonance, scanning electron microscopy(SEM), and dynamic mechanical analysis(DMA). The ethylene content of the PP alloys increased from 2.34% to 26.69% when the propylene/ethylene feed ratio was increased from 66/34 to 54/46(molar ratio). Morevoer, the increment in ethylene content increased the notched Izod impact strength of the resulting PP al-loys. The impact strength of the PP alloy with an ethylene content of 26.69% was 55.8 kJ/m2, which is 12.7 times that of isotactic polypropylene. The results of DMA and SEM analysis reveal that ethylene-propylene random copoly-mer(EPR) in the PP alloy has a low Tg of ca.‒50 °C and a high interface compatibility with the PP matrix. The ex-cellent impact performance of the PP alloy can be attributed to the uniform dispersal of EPR in the alloy particles and PP matrix.