Chain structure of polyethylene/polypropylene in‐reactor alloy synthesized in gas phase with spherical Ziegler–Natta catalyst

Two polyethylene/polypropylene (PE/PP) in‐reactor alloy samples were synthesized by multi‐stage gas‐phase polymerization using a spherical Ziegler–Natta catalyst. The alloys show excellent toughness and stiffness. FTIR, ¹³C‐NMR and thermal analysis proved that the alloys are mainly composed of polyethylene, PE‐block‐PP copolymer and polypropylene. There are also a few percent of ethylene‐propylene segmented copolymer with very low crystallinity. The block copolymer fraction accounts for more than 25 % of the alloy. The role of the block copolymer as compatibilizer between PE and PP is believed to be the key factor that results in the excellent toughness–stiffness balance of the material. Copyright © 2004 Society of Chemical Industry     

Influence of copolymerization conditions on the structure and properties of polyethylene/polypropylene/poly(ethylene‐co‐propylene) in‐reactor alloys synthesized in gas‐phase with spherical ziegler‐natta catalyst

A spherical TiCl₄/MgCl₂‐based catalyst was used in the synthesis of polyethylene/polypropylene/poly (ethylene‐co‐propylene) in‐reactor alloys by sequential homopolymerization of ethylene, homopolymerization of propylene, and copolymerization of ethylene and propylene in gas‐phase. Different conditions in the third stage, such as the pressure of ethylene–propylene mixture and the feed ratio of ethylene, were investigated, and their influences on the compositions, structural distribution and properties of the in‐reactor alloys were studied. Increasing the feed ratio of ethylene is favorable for forming random ethylene–propylene copolymer and segmented ethylene–propylene copolymer, however, slightly influences the formation of ethylene‐b‐propylene block copolymer and homopolyethylene. Raising the pressure of ethylene–propylene mixture results in the increment of segmented ethylene–propylene copolymer, ethylene‐b‐propylene block copolymer, and PE fractions, but exerts a slight influence on both the random copolymer and PP fractions. The impact strength of PE/PP/EPR in‐reactor alloys can be markedly improved by increasing the feed ratio of ethylene in the ethylene–propylene mixture or increasing the pressure of ethylene–propylene mixture. However, the flexural modulus decreases as the feed ratio of ethylene in the ethylene–propylene mixture or the pressure of ethylene–propylene mixture increases. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 102: 2481–2487, 2006     

Structure and morphology of polyethylene/polypropylene in‐reactor alloys synthesized by spherical high‐yield Ziegler–Natta catalyst

A series of spherical polyethylene/polypropylene (PE/PP) in‐reactor alloys were synthesized with spherical high‐yield Ziegler–Natta catalyst by sequential multistage polymerization in slurry. The morphology of PE/PP alloy granule was evaluated by optical microscopy, scanning electron microscopy, and transmission electron microscopy. The results show PE/PP in‐reactor alloy with excellent morphology, high porosity, and narrow distribution of the particle size. The PE/PP in‐reactor alloys show excellent mechanical properties with good balance between toughness and rigidity. It was fractionated into five fractions by temperature‐gradient extraction fractionation, and every fractionation was analyzed by FTIR, ¹³C‐NMR, DSC, and WAXD. The PE/PP in‐reactor alloy was found to contain mainly five portions: PP, PE, segmented copolymer with PP and PE segment of different length, ethylene‐b‐propylene copolymer, and an ethylene–propylene random copolymer. The characteristic chain structure leads to good compatibility between the fractions of the alloy that shows a multiphase structure. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 2075–2085, 2007     

Effect of the structure on the morphology and spherulitic growth kinetics of polyolefin in‐reactor alloys

Four polyolefin in‐reactor alloys with different compositions and structures were prepared by sequential polymerization. All the alloys were fractionated into five fractions: a random copolymer of ethylene and propylene (25°C fraction), an ethylene–propylene segmented copolymer (90°C fraction), an ethylene homopolymer (110°C fraction), an ethylene–propylene block copolymer (120°C fraction), and a propylene homopolymer plus a minor ethylene homopolymer of high molecular weight (>120°C fraction). The effect of the structure on the morphology and spherulitic growth kinetics of the polypropylene (PP) component in the alloys was investigated. The polyolefin alloys containing a suitable block copolymer fraction and a larger amount of PP had a more homogeneous morphology, and the crystalline particles were smaller. Quenching the polyolefin alloys led to smaller crystallites and a more homogeneous morphology as well. Isothermal crystallization was carried out above the melting temperature of polyethylene, and the growth of PP spherulites was monitored with polarized optical microscopy with a hot stage. The alloys with higher propylene contents exhibited a faster spherulitic growth rate. The fold surface free energy was derived, and it was found that a large amount of block copolymer fractions and random copolymer fractions could reduce the fold surface free energy. The structure of the alloys also affected the crystallization regime of PP. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 632–638, 2005     

Study of crystallization and melting behavior of polypropylene‐block‐polyethylenes copolymers fractionated from polypropylene and polyethylene mixtures

A series of ethylene–propylene block copolymer fractions of differing compositions, while still retaining broad molecular weight distributions, were obtained by fractionation of polypropylene (PP) and polyethylene (PE) copolymers prepared by sequential polymerization of ethylene and propylene. The crystallization and melting behavior of the polypropylene‐block‐polyethylene fractions were studied. It was observed that the major component could suppress crystallization of the minor component, leading to a decrease in crystallinity and melting temperature. Non‐isothermal crystallization showed that crystallization of the ethylene block was less influenced by composition and cooling rate than the propylene block. At fast cooling rates, the ethylene block could crystallize prior to the propylene block. Isothermal crystallization kinetics experiments were also conducted. We found that the block copolymers with minor ethylene components had smaller Avrami exponents (n ≈ 1.0), hence indicating a reduced growth dimension of the PE crystals by the pre‐existing PP crystals. On the other hand, the ethylene block exhibited much larger Avrami exponents in those block copolymers with major ethylene contents. Copyright © 2004 Society of Chemical Industry     

Fractionation and characterization of an ethylene–propylene copolymer produced with a MgCl2/SiO2/TiCl4/diester‐type ziegler–natta catalyst

An ethylene–propylene copolymer synthesized with a Ziegler–Natta catalyst was fractionated by a combination of dissolution/precipitation and temperature‐gradient extraction fractionation. The fractions were characterized with ¹³C‐NMR, differential scanning calorimetry, and wide‐angle X‐ray diffraction. The fractionation was carried out mainly with respect to the content of ethylene, but the crystallizable propylene sequences could also exert an influence on the fractionation. The copolymer contained a series of components with wide variations in the compositions. With an increase in the ethylene content, the structure of the fractions became blockier and blockier, and the fraction extracted at 111°C had the blockiest structure. A further increase in the ethylene content led to a decrease in the length and number of the propylene sequences. Differential scanning calorimetry results showed that the composition distribution in single fractions was not homogeneous, and multiple melting peaks were observed. Wide‐angle X‐ray diffraction results revealed both polyethylene and polypropylene crystals in most of the fractions. Short propylene sequences could be included in the polyethylene crystals, and short ethylene sequences could also be incorporated into the polypropylene crystals. The incorporation of propylene sequences into polyethylene crystals strongly depended on the sequence distribution and crystallization conditions. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Influence of polymerization conditions on the structure and properties of polyethylene/polypropylene in‐reactor alloy synthesized in the gas phase with a spherical Ziegler–Natta catalyst

A spherical TiCl₄/MgCl₂‐based catalyst was used in the synthesis of in‐reactor polyethylene/polypropylene alloys by polyethylene homopolymerization and subsequent homopolymerization of propylene in the gas phase. Different conditions in the ethylene homopolymerization stage, such as monomer pressure and polymerization temperature, were investigated, and their influences on the structure and properties of in‐reactor alloys were studied. Raising the polymerization temperature is the most effective way of speeding up polymerization and regulating the ethylene content of polyethylene (PE)/polypropylene (PP) alloys, but it will cause a greater increase in the PE‐b‐PP block copolymer fraction (named fraction D) than in the fraction of PP‐block‐PE in which the PP segments have low or medium isotacticity (named fraction A). Although changing ethylene monomer pressure could influence the ethylene content of PE/PP alloys slightly, it is an effective way of regulating the structural distribution. Reducing the monomer pressure will evidently increase fractions A and D. The mechanical properties of the alloys, including impact strength and flexural modulus, can be regulated in a broad range with changes in polymerization conditions. These properties are highly dependent on the amount, distribution, and chain structure of fractions A and D. The impact strength is affected by both fraction A and fraction D in a complicated way, whereas the flexural modulus is mainly determined by the amount of fraction A. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 101: 2136–2143, 2006     

The functions of crystallizable ethylene‐propylene copolymers in the formation of multiple phase morphology of high impact polypropylene

The functions of crystallizable ethylene‐propylene copolymers in the formation of multiple phase morphology of high impact polypropylene (hiPP) were studied by solvent extraction fractionation, transmission electron microscopy (TEM), selected area electron diffraction (SAED), nuclear magnetic resonance (¹³C‐NMR), and selected reblending of different fractions of hiPP. The results indicate that hiPP contains, in addition to polypropylene (PP) and amorphous ethylene‐propylene random copolymer (EPR) as well as a small amount of polyethylene (PE), a series of crystallizable ethylene‐propylene copolymers. The crystallizable ethylene‐propylene copolymers can be further divided into ethylene‐propylene segmented copolymer (PE‐s‐PP) with a short sequence length of PE and PP segments, and ethylene‐propylene block copolymer (PE‐b‐PP) with a long sequence length of PE and PP blocks. PE‐s‐PP and PE‐b‐PP participate differently in the formation of multilayered core‐shell structure of the dispersed phase in hiPP. PE‐s‐PP (like PE) constructs inner core, PE‐b‐PP forms outer shell, while intermediate layer is resulted from EPR. The main reason of the different functions of the crystallizable ethylene‐propylene copolymers is due to their different compatibility with the PP matrix. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Preparation and characterization of high MFR polypropylene and polypropylene/poly(ethylene‐co‐propylene) in‐reactor alloys

In this work, high melt flow rate (MFR) polypropylene (HF‐PP) and polypropylene/poly(ethylene‐co‐propylene) in‐reactor alloys (HF‐PP/EPR) with MFR ≈ 30 g/10 min were synthesized by spherical MgCl₂‐supported Ziegler–Natta catalyst with cyclohexylmethyldimethoxysilane (CHMDMS) or dicyclopentyldimethoxysilane (DCPDMS) as external donor (De). The effects of De on polymerization activity, chain structure, mechanical properties, and phase morphology of HF‐PP and HF‐PP/EPR were studied. Adding CHMDMS caused more sensitive change of the polymers MFR with H₂ than DCPDMS, and produced PP/EPR alloys containing more random ethylene‐propylene copolymer (r‐EP) and segmented ethylene‐propylene copolymer (s‐EP). CHMDMS also caused formation of s‐EP with higher level of blockiness than DCPDMS. HF‐PP/EPR alloy prepared in the presence of DCPDMS exhibited higher flexural properties but lower impact strength than that prepared with CHMDMS. Toughening efficiency of the rubber phase was nearly the same in the alloys prepared using CHMDMS or DCPDMS as De, but stiffness of the alloy can be improved by using DCPDMS. © 2015 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016 , 133, 42984.     

Structure and morphology of a commercial high‐impact polypropylene in‐reactor alloy synthesized using a spherical Ziegler–Natta catalyst

A commercial high‐impact polypropylene (hiPP) was fractionated by temperature‐gradient elution fractionation into nine fractions. All fractions were studied using Fourier transform infrared spectroscopy and differential scanning calorimetry. The amount of ethylene in the fractions was also determined. The results demonstrate that the ethylene–propylene statistical copolymer (or ethylene–propylene rubber, EPR) content in this hiPP is rather low and the amounts of ethylene–propylene segmented copolymer and ethylene–propylene block copolymer (that act as adhesive and compatibilizer between elastomeric phase and matrix, respectively) are negligible. Furthermore, the morphology of the resin was studied using scanning electron microscopy observations of microtome‐cut original and etched samples, which reveals that EPR particles are too large and their distribution inside the matrix is not uniform. Copyright © 2010 Society of Chemical Industry     

Multilayered core–shell structure of the dispersed phase in high‐impact polypropylene

The multiphase morphology of high impact polypropylene (hiPP), which is a reactor blend of polypropylene (PP) with ethylene–propylene copolymer, was investigated by transmission electron microscopy, selected area electron diffraction, atomic force microscopy, and field‐emission scanning electron microscopy techniques in conjunction with an analysis of the hiPP composition and chain structure based on solvent fractionation, ¹³C‐NMR, and differential scanning calorimetry measurements. A multilayered core–shell structure of the dispersed phase of hiPP in solution‐cast films and the bulk was observed. The inner core was mainly composed of polyethylene (including its long blocks) together with part of PP, the intermediate layer was ethylene–propylene random copolymer, and the outer shell consisted of ethylene–propylene multiblock copolymers. The formation process and controlling factors of the multilayered core–shell structure are discussed. This kind of multiphase morphology of hiPP caused the material to possess both a high rigidity and high toughness. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

Compatibilization of poly(vinyl chloride) with polyamide and with polyolefin by using poly(lauryllactam‐random‐caprolactam‐block‐caprolactone)

The compatibilization of various poly(vinyl chloride) (PVC) blends was investigated. The blend systems were PVC‐polyamide 12 (PA12), PVC‐polypropylene (PP), and PVC‐ethylene‐propylene‐diene rubber (EPDM) with a new compatibilizing agent, random‐block terpolymer poly(ω‐lauryllactam‐random‐?‐caprolactam‐block‐?‐caprolactone) or systems containing these copolymers. The results were compared to those obtained in previous studies using poly(ω‐lauryllactam‐block‐?‐caprolactone) copolymer. The new block copolymer was specially synthesized by reactive extrusion. Observation by scanning electron microscopy (SEM) revealed that compatibilized blends had a finer morphology than the noncompatibilized blends. Addition of 10 weight percent (wt%) of block copolymer proved to be sufficient to give a significant improvement of the mechanical properties of the immiscible PVC blends at room temperature and at high temperatures that were above the glass transition temperature of PVC. For polyolefins, a three‐component compatibilizing system including maleated polypropylene, polyamide 12, and block copolymer was used. It was found that poly(ω‐lauryllactam‐random‐?‐caprolactam‐block‐?‐caprolactone) was the more efficient compatibilizing agent for the modification of PVC‐polyamide 12, PVC‐polypropylene, and PVC‐ethylene‐propylene‐diene rubber blends. J. VINYL. ADDIT. TECHNOL., 11:95–110, 2005. © 2005 Society of Plastics Engineers     

Influences of copolymerization conditions on the structure and properties of isotactic polypropylene/ethylene–propylene random copolymer in situ blends

A spherical TiCl₄/MgCl₂‐based catalyst was used in the synthesis of in situ isotactic polypropylene/ethylene–propylene random copolymer blends by propylene bulk polymerization and subsequent gas‐phase copolymerization of ethylene with propylene. Different copolymerization conditions, such as the reaction time, monomer pressure, and composition, were investigated, and their influences on the structure and properties of the products were studied. Raising the monomer pressure was the most effective way of speeding up the copolymerization, but it caused more increases in the random copolymer than the block copolymer fractions. Increasing the ethylene content of the monomer feed also resulted in higher reaction rates and copolymer contents, but the ethylene contents of both the random and block copolymer fractions were also raised. In situ blends that contain more than 50 wt % copolymer were prepared. The mechanical properties of the blends, including the impact strength and flexural modulus, were regulated in a rather broad range with changes in the copolymerization conditions. The properties were highly dependent on the amount, distribution, and chain structure of the copolymer fractions. The impact strength was influenced by both the random copolymer and block copolymer portions in a complicated way, whereas the flexural modulus was mainly determined by the amount of random copolymer. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 84: 445–453, 2002; DOI 10.1002/app.10415     

Comparison of olefin copolymers as compatibilizers for polypropylene and high‐density polyethylene

Some polyolefin elastomers were compared as compatibilizers for blends of polypropylene (PP) with 30 wt % high‐density polyethylene (HDPE). The compatibilizers included a multiblock ethylene–octene copolymer (OBC), two statistical ethylene–octene copolymers (EO), two propylene–ethylene copolymers (P/E), and a styrenic block copolymer (SBC). Examination of the blend morphology by AFM showed that the compatibilizer was preferentially located at the interface between the PP matrix and the dispersed HDPE particles. The brittle‐to‐ductile (BD) transition was determined from the temperature dependence of the blend toughness, which was taken as the area under the stress–strain curve. All the compatibilized blends had lower BD temperature than PP. However, the blend compatibilized with OBC had the best combination of low BD temperature and high toughness. Examination of the deformed blends by scanning electron microscopy revealed that in the best blends, the compatibilizer provided sufficient interfacial adhesion so that the HDPE domains were able to yield and draw along with the PP matrix. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Structure and properties of impact copolymer polypropylene. I. Chain structure

In this work, impact copolymer polypropylene (ICPP) was fractionated into 4 fractions. ICPP and the 4 fractions were studied using Fourier transform infrared and ¹³C nuclear magnetic resonance analysis. The results demonstrate that fraction A is ethylene–propylene rubber, fraction B is ethylene–propylene (EP) segmented copolymer, fraction C is ethylene–propylene block copolymer, and fraction D is polypropylene with a few ethylene monomers in the chain. The differences in properties between different impact copolymer polypropylenes should be due to their fractions' differences in composition and chain sequence structure. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 93–101, 1999     

New synthesis methods for polypropylene‐co‐ethylene‐propylene rubber

In this research, the reinforcement of polypropylene (PP) was studied using a new method that is more practical for synthesizing polypropylene‐block‐poly(ethylene‐propylene) copolymer (PP‐co‐EP), which can be used as a rubber toughening agent. This copolymer (PP‐co‐EP) could be synthesized by varying the feed condition and changing the feed gas in the batch reactor system using Ziegler–Natta catalysts system at a copolymerization temperature of 10°C. The ¹³C‐NMR tested by a 21.61‐ppm resonance peak indicated the incorporation of ethylene to propylene chains that could build up the microstructure of the block copolymer chain. Differential scanning calorimetry (DSC), scanning electron microscopy (SEM), and dynamic mechanical analysis (DMA) results also confirmed these conclusions. Under these conditions, the morphology of copolymer trapped in PP matrix could be observed and the copolymer T_g would decrease when the amount of PP‐co‐EP was increased. DMA study also showed that PP‐co‐EP is good for the polypropylene reinforcement at low temperature. Moreover, the PP‐co‐EP content has an effect on the crystallinity and morphology of polymer blend, i.e., the crystallinity of polymer decreased when the PP‐co‐EP content increased, but tougher mechanical properties at low temperature were observed. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3609–3616, 2007     

Study on thermal behavior of impact polypropylene copolymer and its fractions

An impact polypropylene copolymer (IPC) was fractionated into three fractions using n‐octane as solvent by means of temperature‐gradient extraction fractionation. The glass transitions, melting, and crystallization behavior of these three fractions were studied by modulated differential scanning calorimeter (MDSC) and wide‐angle X‐ray diffraction (WAXD). In addition, successive self‐nucleation and annealing (SSA) technique was adopted to further examine the heterogeneity and the structure of its fractions. The results reveal that the 50°C fraction (F₅₀) mainly consists of ethylene‐propylene random copolymer and the molecular chains may contain a few of short but crystallizable propylene and/or ethylene unit sequences; moreover, the lamellae thicknesses of the resulting crystals are extremely low. Furthermore, 100°C fraction (F₁₀₀) mainly consist of some branched polyethylene and various ethylene‐propylene block copolymers in which some ethylene and propylene units also randomly arrange in certain segments, and some polypropylene segments can form crystals with various lamellae thickness. An obvious thermal fractionation effect for F₁₀₀ samples after being treated by SSA process is ascribed to the irregular and nonuniform arrangement of ethylene and propylene segments. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

NMR,differential scanning calorimetry,and Fourier transform infrared characterization of the crystalline degree and crystallite dimensions of ethylene runs in isotactic polypropylene/ethylene–propylene copolymer blends (iPP/EP)

High‐resolution solid‐state ¹³C‐NMR, differential scanning calorimetry, and Fourier transform infrared spectroscopy were used to compare the very low crystalline degree and crystallite dimensions of ethylene runs in a series of isotactic polypropylene/ethylene–propylene copolymer blends exhibiting a range of properties. Results obtained from the three techniques on samples with the same thermal history are in a satisfying qualitative agreement. They show that the morphology of the polyethylene domains is only very slightly dependent on the viscosity ratio of the two blend components. On the opposite, it is largely governed by the ethylene content of the ethylene–propylene copolymer. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 3165–3172, 1999     

Structural characterization of reactor blends of polypropylene and ethylene‐propylene rubber

Blends of isotactic polypropylene (PP), ethylene‐propylene rubber copolymer (EPR), and ethylene‐propylene crystalline copolymer (EPC) can be produced through in situ polymerization processes directly in the reactor and blends with different structure and composition can be obtained. In this work we studied the structure of five reactor‐made blends of PP, EPR, and EPC produced by a Ziegler‐Natta catalyst system. The composition of EPR was related to the ratio between ethylene and propylene used in the copolymerization step. The ethylene content in the EPR was in the range of 50–70 mol %. The crystallization behavior of PP and EPC in the blends was influenced by the presence of the rubber, and some specific interactions between the components could be established. By preparative temperature rising elution fractionation (P‐TREF) analysis, the isolation and characterization of crystalline EPC fractions were made. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 2155–2162, 2004     

FI Catalysts: A New Family of High Performance Catalysts for Olefin Polymerization

This paper reviews a new family of olefin polymerization catalysts. The catalysts, named FI catalysts, are based on non‐symmetrical phenoxyimine chelate ligands combined with group 4 transition metals and were developed using “ligand‐oriented catalyst design”. FI catalysts display very high ethylene polymerization activities under mild conditions. The highest activity exhibited by a zirconium FI catalyst reached an astonishing catalyst turnover frequency (TOF) of 64,900 s ^–1 atm ^–1, which is two orders of magnitude greater than that seen with Cp₂ZrCl₂ under the same conditions. In addition, titanium FI catalysts with fluorinated ligands promote exceptionally high‐speed, living ethylene polymerization and can produce monodisperse high molecular weight polyethylenes (M_w/M_n<1.2, max. M_n>400,000) at 50 °C. The maximum TOF, 24,500 min ^–1 atm ^–1, is three orders of magnitude greater than those for known living ethylene polymerization catalysts. Moreover, the fluorinated FI catalysts promote stereospecific room‐temperature living polymerization of propylene to provide highly syndiotactic monodisperse polypropylene (max. [rr] 98%). The versatility of the FI catalysts allows for the creation of new polymers which are difficult or impossible to prepare using group 4 metallocene catalysts. For example, it is possible to prepare low molecular weight (M_v∼10³) polyethylene or poly(ethylene‐co‐propylene) with olefinic end groups, ultra‐high molecular weight polyethylene or poly(ethylene‐co‐propylene), high molecular weight poly(1‐hexene) with atactic structures including frequent regioerrors, monodisperse poly(ethylene‐co‐propylene) with various propylene contents, and a number of polyolefin block copolymers [e.g., polyethylene‐b‐poly(ethylene‐co‐propylene), syndiotactic polypropylene‐b‐poly(ethylene‐co‐propylene), polyethylene‐b‐poly(ethylene‐co‐propylene)‐b‐syndiotactic polypropylene]. These unique polymers are anticipated to possess novel material properties and uses.