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     

Fabrication of polypropylene blends with excellent low‐temperature toughness and balanced toughness‐rigidity by a combination of EPR and SEEPS

To overcome serious rigidity depression of rubber‐toughened plastics and fabricate a rigidity‐toughness balanced thermoplastic, a combination of styrene‐[ethylene‐(ethylene‐propylene)]‐styrene block copolymer (SEEPS) and ethylene‐propylene rubber (EPR) was used to toughen polypropylene. The dynamic mechanical properties, crystallization and melting behavior, and mechanical properties of polypropylene (PP)/EPR/SEEPS blends were studied in detail. The results show that the combination of SEEPS and EPR can achieve the tremendous improvement of low‐temperature toughness without significant strength and rigidity loss. Dynamic mechanical properties and phase morphology results demonstrate that there is a good interfacial strength and increased loss of compound rubber phase comprised of EPR component and EP domain of SEEPS. Compared with PP/EPR binary blends, although neither glass transition temperature (T_g) of the rubber phase nor T_g of PP matrix in PP/EPR/SEEPS blends decreases, the brittle‐tough transition temperature (T_bd) of PP/EPR/SEEPS blends decreases, indicating that the increased interfacial interaction between PP matrix and compound rubber phase is also an effective approach to decrease T_bd of the blends so as to improve low‐temperature toughness. The balance between rigidity and toughness of PP/EPR/SEEPS blends is ascribed to the synergistic effect of EPR and SEEPS on toughening PP. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45714.     

Influence of cocatalyst on the structure and properties of polypropylene/poly (ethylene‐co‐propylene) in‐reactor alloys prepared by MgCl2/TiCl4/diester type Ziegler‐Natta catalyst

In this work, a series of polypropylene/poly(ethylene‐co‐propylene) (iPP/EPR) in‐reactor alloys were prepared by MgCl₂/TiCl₄/diester type Ziegler‐Natta catalyst with triethylaluminium/triisobutylaluminium (TEA/TIBA) mixture as cocatalyst. The influence of cocatalyst and external electron donor, e.g., diphenyldimethoxysilane (DDS) or dicyclopentyldimethoxysilane (D ‐donor), on the structure and mechanical properties of iPP/EPR in‐reactor alloys were studied and discussed. According to the characterization results, PP/EPR was mainly composed of random poly(ethylene‐co‐propylene), segmented poly(ethylene‐co‐propylene), and high isotactic PP. Using TEA/TIBA mixture as cocatalyst and DDS as external electron donor, as TEA/TIBA ratio increased, the impact strength of iPP/EPR in‐reactor alloys had an increasing trend. Using TEA/TIBA mixture as cocatalyst and D ‐donor as external electron donor, the impact strength of iPP/EPR in‐reactor alloy were dramatically improved. In this case, the iPP/EPR in‐reactor alloy prepared at TEA: TIBA = 4 : 1 was the toughest. The influence of cocatalyst and external electron donor on the flexural modulus and flexural strength could be ignored. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

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     

Effect of composition and component structure on thermal behavior and miscibility of polypropylene catalloys

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. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007     

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     

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     

Structure and properties of polypropylene alloy in situ blends

A series of polypropylene (PP) alloys containing different ethylene contents have been prepared by the in situ sequential polymerization technique, using Ziegler–Natta catalyst (MgCl₂/TiCl₄/BMF; BMF is 9,9‐bis(methoxymethyl)fluorine, as an internal donor) without any external donor. The structure and properties of PP alloys obtained have been investigated by nuclear magnetic resonance, Fourier transform infrared spectroscopy, dynamic mechanical analysis, differential scanning calorimetry, and scanning electron microscopy (SEM). The results have suggested that PP alloys are the complex mixtures containing PP, the copolymer with long sequence ethylene chain, ethylene‐propylene rubber (EPR), and block copolymer etc. In the alloys, PP, EPR, and the copolymer with long sequence ethylene chain are partially compatible. The investigation of the mechanical properties indicates that notched Izod impact strength of PP alloy greatly increases at 16°C/?20°C in comparison with that of pure PP. The noticeable plastic deformation is observed in SEM photograph. The increase in the toughness, the mechanical strength of PP alloy decreases to a certain extent. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 4804–4810, 2006     

Synthesis of polypropylene graft copolymers from a hydroxyl‐groups‐containing polypropylene precursor via atom‐transfer radical polymerization

Isotactic polypropylene graft copolymers, isotactic[polypropylene‐graft‐poly(methyl methacrylate)] (i‐PP‐g‐PMMA) and isotactic[polypropylene‐graft‐polystyrene] (i‐PP‐g‐PS), were prepared by atom‐transfer radical polymerization (ATRP) using a 2‐bromopropionic ester macro‐initiator from functional polypropylene‐containing hydroxyl groups. This kind of functionalized propylene can be obtained by copolymerization of propylene and borane monomer using isospecific MgCl₂‐supported TiCl₄ as catalyst. Both the graft density and the molecular weights of i‐PP‐based graft copolymers were controlled by changing the hydroxyl group contents of functionalized polypropylene and the amount of monomer used in the grafting reaction. The effect of i‐PP‐g‐PS graft copolymer on PP‐PS blends and that of i‐PP‐g‐PMMA graft copolymer on PP‐PMMA blends were studied by scanning electron microscopy. Copyright © 2006 Society of Chemical Industry     

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     

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     

Chain structure and mechanical properties of polyethylene/polypropylene/poly(ethylene‐co‐propylene)in‐reactor alloys synthesized with a spherical Ziegler–Natta catalyst by gas‐phase polymerization

Two polyethylene/polypropylene/poly(ethylene‐co‐propylene) in‐reactor alloy samples with a good polymer particle morphology were synthesized by sequential multistage gas‐phase polymerization with a spherical Ziegler–Natta catalyst. The alloys showed excellent mechanical properties, including both toughness and stiffness. With temperature‐gradient extraction fractionation, both alloys were fractionated into five fractions. The chain structures of the fractions were studied with Fourier transform infrared, ¹³C‐NMR, and thermal analysis. The alloys were mainly composed of polyethylene, polyethylene‐b‐polypropylene block copolymer, and polypropylene. There also were minor amounts of an ethylene–propylene segmented copolymer with very low crystallinity and an ethylene–propylene random copolymer. The block copolymer fraction accounted for more than 44 wt % of the alloys. The coexistence of these components with different structures was apparently the key factor resulting in the excellent toughness–stiffness balance of the materials. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 97: 640–647, 2005     

Probing into the pristine basic morphology of high impact polypropylene particles

In this paper, the pristine basic morphology of high impact polypropylene (hiPP) particles prepared with an industrial MgCl₂/TiCl₄ Ziegler–Natta catalyst undergoing sequentially occurred propylene (P) homopolymerization and ethylene (E)/propylene copolymerization has been probed mainly using transmission electron microscopy (TEM) techniques including plain TEM and the advanced transmission electron microtomography (TEMT). It is revealed that the basic structure units comprising a whole hiPP particle are the submicron PP (polypropylene) globule and nano-sized EP (ethylene-co-propylene) droplet. EP rubber (EPR) domain is formed by the agglomeration of EP droplets. Continually formed EP droplets turn to fill, from inside out, the micro- and macro-pores inside the preformed PP skeleton, affording different-sized EPR domains. Taking the two basic structure units into account, new quaternary structure model describing the manifold structures of hiPP particles has been proposed. From these findings, it is suggested that, to gain hiPP polymers with excellent stiffness/toughness-balanced properties, it is crucial to control the first-staged propylene homopolymerization alongside a rational design of the catalyst architecture to accomplish desired EPR dispersion morphologies that dictate hiPP properties.     

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     

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     

Mechanical and thermal properties of toughened polypropylene composites

The mechanical, thermal, and structural properties of a new flexible composite containing polypropylene fiber (PP) in a random poly(propylene‐co‐ethylene) (PPE) matrix with ethylene–propylene elastomer (EP) was investigated with emphasis on the effect of EP elastomer concentration. The intrinsic composition of the composites, toughening of the matrix with EP and the fiber–matrix interface determined the properties of the composites. Through the incorporation of EP elastomer into the polypropylene–poly (propylene‐co‐ethylene) (all‐PP) composite, tensile and storage modulus (E′) decreased, flexural modulus and loss modulus (E″, damping) increased slightly to 0.15 EP and then decreased. There was an increase in impact resistance for the toughened composites, with about 100% increase in comparison with an untoughened all‐PP composite. The composition corresponding to 0.20 weight fraction EP gave optimum impact and mechanical properties. Creep resistance of the composite decreased with increasing EP content, but recovery showed an increase with increasing EP content up to 0.20. Fracture surfaces of composites after impact tests were studied with scanning electron microscopy. Moreover, the use and limitation of theoretical equations to predict the tensile and flexural modulus of the flexible PP composite is discussed. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007     

Elaboration of low viscosity and high impact polypropylene blends through reactive extrusion

In this work, a reactive high flow polypropylene, PP800 (η₀ = 40 Pa s, 190°C), is extruded with a commercial compound of polypropylene and ethylene‐propylene random copolymer (η₀ = 3000 Pa s, 190°C). On one hand, the fluidity of resulting blends is highly increased but, on the other hand, matrix degradation leads to a strong decrease of the impact behavior and tensile strain. Then, the addition of 10 wt% of propylene‐based copolymer (PBC) leads to a very interesting impact enhancement while keeping high fluidity. A study of morphological, thermal, and dynamical thermal mechanical properties reveal the anchoring of semi crystalline propylene segments of PBC droplets at the interface with the PP matrix. On the contrary, the addition of ethylene‐based copolymer (EBC) is not able to restore satisfactory impact properties. POLYM. ENG. SCI., 56:418–426, 2016. © 2016 Society of Plastics Engineers     

Surface functionalization of polypropylene by entrapment of polypropylene‐grafted‐poly(ethylene glycol)

A surface functionalization polypropylene was prepared by entrapment a copolymer of polypropylene‐grafted‐poly(ethylene glycol) into polypropylene. The effects of structure of copolymer, contact dies, and content of modifiers were studied. The results of attenuated total reflection infrared spectroscopy(ATR‐FTIR) and contact angle measurements indicated that PP‐g‐PEG could preferably diffuse onto the surface and effectively increase the hydrophilicity of PP. PPw‐g‐PEG with lower PEG contents, lower molecular weight of PPw and PEG had better selective enrichment on the surface of PP blend film. By grafting of PEG‐OH onto the MPP, PP macromolecular surface modifier with better solvent‐resistance than that of PEG can be achieved. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

Melt‐electrospun fibers obtained from polypropylene/poly(ethylene‐co‐vinyl alcohol)/polypropylene three‐layer films

Production of polypropylene (PP) nanofibers below 1 μm in average diameter is difficult with conventional melt‐spinning. A nozzle‐free melt‐type electrospinning (M‐ESP) system with a line‐like CO₂ laser beam melting device were used to produce PP nanofibers. To achieve the purpose, core [poly(ethylene‐co‐vinyl alcohol) (EVOH)]–clad (PP) nanofibers (average diameter, 0.88 μm) were fabricated from PP/EVOH/PP three‐layer films using the M‐ESP. The core–clad structure was formed by a wrapping phenomenon caused by the difference in the melt flow rates (MFRs) of PP and EVOH melts. Hollow PP nanofibers were obtained from the core–clad nanofibers by extraction of EVOH. Nanofiber diameter and hollow wall thickness could be altered by changing the MFR of the PP melt. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 46393.     

Influence of propylene‐based elastomer on stress‐whitening for impact copolymer

Two pure impact copolymer polypropylenes (ICP), one pure homo‐polypropylene (HPP) and their compounds with different type and fraction of Vistamaxx? propylene‐based elastomer (“Vistamaxx”) were used to investigate the stress whitening activated in the impact processes via ultra‐small‐angle X‐ray scattering technique. The whitening presented in ICP is confirmed to be caused by the interfaces existed between ethylene‐propylene (EP) rubber and polypropylene matrix, such kind whitening is apparently unlike the one initiated in the crystal phase of HPP. In this study, Vistamaxx with high crystallinity can adjust the compatibility of EP rubber and PP matrix which results in a reduction of interfaces, thus, a phenomenon of reduced stress whitening can be observed in blends of ICP with Vistamaxx. However, the enhancement of stress whitening can be found in blends of ICP with Vistamaxx which occupied low crystallinity. Such behaviors can be assigned to the poor compatibility between Vistamaxx and PP matrix. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44747.