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     

Characterization and properties of polypropylene‐block‐poly(ethylene‐co‐propylene) synthesized by short‐period polymerization

The morphology and mechanical properties of novel block copolymers consisting of isotactic polypropylene (PP) and ethylene–propylene rubber (EPR) synthesized by a short‐period polymerization method were examined using differential scanning calorimetry, atomic force microscopy, dynamic mechanical analysis, and a rheooptical technique. It was found that the novel block copolymers show a single glass transition and EPR segments are trapped into the amorphous region of PP. Furthermore, the rheooptical analysis demonstrates that a drawing process of the EPR‐rich block copolymer induces orientation of the PP lamellae in the EPR matrix. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 74: 958–964, 1999     

Effect of center block structure on the physical and rheological properties of ABA block copolymers. Part II. Rheological properties

The effect of the chemical structure of the center block on the rheological properties of ABA block copolymers with polystyrene end blocks has been investigated. The chemical structure of the center blocks investigated in the present paper are polybutadiene, polyisoprene, ethylene/butene copolymer, ethylene/propylene copolymer and polydimethyl-siloxane. The chemical structure of the center block was found to have a pronounced effect on the rheological properties of the ABA block copolymer melts. The long range relaxation times of these block copolymer melts increases with increasing incompatibility between the styrene block and the center block. However, the rheological properties of the block copolymers are not influenced significantly by the glass transition or the entanglement molecular weight of the center block.     

乙丙嵌段共聚物相对分子质量及链结构对PP/EPR共混体系结构与性能的影响

设计合成了一系列不同相对分子质量和乙烯平均序列长度的乙丙嵌段共聚物（EP）,并将其作为聚丙烯（PP）/二元乙丙橡胶（EPR）共混体系的增容剂,考察了EP用量、相对分子质量及乙烯平均序列长度对共混体系性能及分散相形态演变的影响。结果表明,EP增容PP/EPR体系时存在最佳添加量,少量EP的加入可有效提高PP/EPR共混体系的抗冲击性能,并对分散相尺寸及形态起到良好的调控作用;同时,EP的相对分子质量越大对共混体系的冲击性能提高越明显,EP的组成与EPR越接近,对共混体系的增容效果越明显。     

Relation between molecular structure and flow instability for ethylene/α-olefin copolymers

Surface instabilities in a capillary extrusion have been studied for various ethylene/α-olefin copolymers. It is found that the onset stress of shark-skin failure for ethylene/1-hexene copolymer (EHR) decreases rapidly with increasing 1-hexene content, whereas that of ethylene/propylene copolymer (EPR) is independent of propylene content in the experimental region. Consequently, EHR with high 1-hexene content exhibits shark-skin at low stress level compared to EPR. Lower rubbery plateau modulus, leading to higher Deborah number at the same stress level, is attributed to the lower onset stress. Further, the low entanglement density will cause cracks at lower stress level like glassy polymers, which is also responsible for the low onset stress for shark-skin.     

抗冲聚丙烯结构与性能研究

对部分国内外抗冲聚丙烯(PP)产品进行了微观形态和结构分析，研究其对材料宏观力学性能的影响。实验结果表明：抗冲PP是一个含有PP均聚物、丙烯与乙烯-丙烯两嵌段共聚物、乙丙橡胶(EPR)、聚乙烯均聚物等的多相体系。EPR的分子序列结构对聚合物抗冲击性能起主要作用。在序列结构中，丙烯、乙烯单体在分子链上的位置交换越频繁，抗冲击性能越得到提高。丙烯序列平均长度的增大对抗冲击性能有一定的削弱作用。     

PP/PE blends. IV. Characterization and compatibilization of blends of postconsumer resin with virgin PP and HDPE

The mechanical properties of blends of isotactic polypropylene and high-density polyethylene with a postconsumer resin (recycled dairy containers) were investigated over the entire composition range. Modification of these blends with an ethylene/propylene/diene copolymer or an ethylene/vinyl acetate copolymer was also investigated. Isotactic polypropylene/postconsumer resin blends have satisfactory impact and tensile properties at postconsumer resin contents of less than 50% for certain applications. At higher postconsumer resin contents, the tensile properties were adversely affected. The impact properties remained satisfactory. Addition of an ethylene/propylene/diene copolymer improved the mechanical properties of these blends to levels equal to or greater than those for neat isotactic polypropylene. Ethylene/vinyl acetate copolymers were also able to improve the mechanical properties, but not as efficiently as did the ethylene/propylene/diene copolymer. Blends of high-density polyethylene and a postconsumer resin had poor impact and tensile properties. Although the ethylene/propylene/diene copolymer and ethylene/vinyl acetate copolymers were able to improve these properties, the improvement was insufficient for general recycling, except at lower (≤25%) postconsumer resin contents. © 1998 John Wiley & Sons, Inc. J Appl Polym Sci 70: 2081–2095, 1998     

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     

The Use of Ethylene/Propylene Copolymers as Compatibilizers for Recycled Polyolefin Blends

Compatibilizing effects of ethylene/propylene (EPR) diblock copolymers on the morphology and mechanical properties of immiscible blends produced from recycled low‐density polyethylene (PE‐LD) and high‐density polyethylene (PE‐HD) with 20 wt.‐% of recycled poly(propylene) (PP) were investigated. Two different EPR block copolymers which differ in ethylene monomer unit content were applied to act as interfacial agents. The morphology of the studied blends was observed by scanning‐ (SEM) and transmission electron microscopy (TEM). It was found that both EPR copolymers were efficient in reducing the size of the dispersed phase and improving adhesion between PE and PP phases. Addition of 10 wt.‐% of EPR caused the formation of the interfacial layer surrounding dispersed PP particles with the occurrence of PE‐LD lamellae interpenetration into the layer. Tensile properties (elongation at yield, yield stress, elongation at break, Young's modulus) and notched impact strength were measured as a function of blend composition and chemical structure of EPR. It was found that the EPR with a higher content of ethylene monomer units was a more efficient compatibilizer, especially for the modification of PE‐LD/PP 80/20 blend. Notched impact strength and ductility were greatly improved due to the morphological changes and increased interfacial adhesion as a result of the EPR localization between the phases. No significant improvements of mechanical properties for recycled PE‐HD/PP 80/20 blend were observed by the addition of selected block copolymers.     

Facile synthesis of ethylene–propylene fully alternating copolymer and comparison with random copolymer of similar composition

A precisely sequenced ethylene–propylene (EP) fully alternating copolymer was synthesized via trans‐1,4‐polymerization of isoprene catalyzed by Ziegler–Natta catalyst followed by hydrogenation. This EP copolymer was used as model polymer for studying structure–property relationship. An ethylene–propylene random copolymer (ethylene–propylene rubber [EPR]) with similar ethylene content was also prepared for comparison, and the effect of comonomer sequence distribution on properties was investigated. The copolymer chain structures were monitored by ¹H and ¹³C NMR and Fourier translation infrared. Differential scanning calorimetry, thermogravimetric analysis, dynamic mechanical analysis, and tensile tests were employed to determine the thermal and mechanical properties. The fully alternating copolymer EP gives a more precise glass transition comparing than EPR. Further understanding on thermal properties and aggregation behavior of ethylene–propylene copolymers is made possible by this comparative study. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2018 , 135, 45816.     

气相法PP洗衣机专用树脂结构与性能研究

以核磁共振碳谱、差示扫描量热法、凝胶渗透色谱，扫描电子显微镜和原子力显微镜等手段对聚丙烯共聚物进行结构与性能研究，发现气相法聚丙烯聚物中含有更多的乙丙接点及多种乙丙嵌段结构，分子链柔性好，其分子量分布宽，乙丙橡胶的重均分子量较大，粒径较小，分散均一，对提高冲击强度有利，其结晶细密，结晶温度高，速度快、对提高刚性，改善加工性能有利。     

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     

Effect of diblock copolymers on morphology and mechanical properties for syndiotactic polystyrene/ethylene‐propylene copolymer blends

Interfacial agents are often used to compatibilize immiscible polymer blends. They are known to reduce the interfacial tension, homogenize the morphology, and improve adhesion between phases. In this study, two diblock copolymers of styrene/ethylene‐propylene (SEP), which have different molecular weights, were used to compatibilize a blend of syndiotactic polystyrene (sPS) 75% and ethylene‐propylene rubber (EPR) 25% so as to extend the applications of sPS as incoming thermoplastics. The morphological analysis and emulsification curve, which relates the average size of the dispersion particles to the concentration of diblock copolymers added, was used to investigate the efficiency of the interfacial agents on the blend morphology. A notched izod impact test and a tensile test were also performed to determine the compatibilization effect of different molecular weight copolymers on the mechanical properties of the blends and to establish links between morphology and mechanical properties. Results suggest that the lower molecular weight diblock copolymer showed an effective emulsifying capacity for sPS/ERP immiscible blend in morphology and mechanical properties. © 2004 Wiley Periodicals, Inc. J Appl Polym Sci 91:3618–3626, 2004     

Defining the distribution of ethylene-propylene copolymer phases in heterophasic ethylene-propylene copolymers by a sequential xylene extraction method: Chemical and morphological analysis

Sequential xylene extraction (SXE) in combination with scanning electron microscopy (SEM) and high temperature solvent gradient interaction chromatography (HT-SGIC) were employed for the detailed visualisation and understanding of the evolution of phase morphology in heterophasic ethylene-propylene copolymer (HEPC) particles. The study focused on sequentially extracting the soluble EP rubber phase and EP block or segmented copolymers by SXE at various temperatures. Major changes in the particle morphology (significant increase in both size and number of voids in the particles) after SXE were revealed using SEM imaging. These void structures are believed to result from the amorphous phase (EPR) being removed during the xylene extraction which was further confirmed by differential scanning calorimetry (DSC), high temperature ¹³C NMR spectroscopy and HT-SGIC. The extractables obtained at 100 °C were found to be a mixture of EP random copolymers, semi-crystalline EP (block or segmented) copolymers, as well as iPP and PE homopolymers. Upon complete dissolution of the particles by SXE at 100 °C, significant amounts of the EP rubber fractions were obtained. Our results show a very heterogeneous distribution of EPR components with varying chemical compositions in HEPC particles produced by dual-reactor processes. For the layered structure observed from this study, truly amorphous EP rubber was found in the outer most regions followed by continuous regions of EP random copolymers having increasing ethylene contents. Propylene-rich EPR, extracted at temperatures of 100 and 130 °C, was observed as the inner EPR phase. Semi-crystalline EP (segmented or block copolymer) and PE homopolymer were detected as intermediate structures between these two EPR regions, inside and outside the pores of the iPP particles. Based on these findings a modified multi-layered core–shell structure was proposed. The results obtained by the proposed SXE fractionation method and its combination with various analytical approaches are found to be very effective for the investigation of the phase composition present in HEPC particles. The present approach is general and can also be used for other multiphase semi-crystalline polyolefins.     

Mechanical properties and morphology of crosslinked PP/PE blends and PP/PE/propylene–ethylene copolymer blends

Blending is an effective method for improving polymer properties. However, the problem of phase separation often occurs due to incompatibility of homopolymers, which deteriorates the physical properties of polyblends. In this study, isotactic polypropylene was blended with low-density polyethylene. Crosslinking agent and copolymers of propylene and ethylene (either random copolymer or block copolymer) were added to improve the interfacial adhesion of PP/LDPE blends. The tensile strength, heat deflection temperature, and impact strength of these modified PP/PE blends were investigated. The microstructures of polyblends have been studied to interpret the mechanical behavior through dynamic viscoelasticity, wide-angle X-ray diffraction, differential scanning calorimetry, picnometry, and scanning electron microscopy. The properties of crosslinked PP/PE blends were determined by the content of crosslinking agent and processing method. For the material blended by roll, a 2% concentration of peroxide corresponded to a maximum tensile strength and minimum impact strength. However, the mechanical strength of those products blended by extrusion monotonously decreased with increasing peroxide content because of serious degradation. The interfacial adhesion of PP/PE blends could be enhanced by adding random or block copolymer of propylene and ethylene, and the impact strength as well as ductility were greatly improved. Experimental data showed that the impact strength of PP/LDPE/random copolymer ternary blend could reach as high as 33.3 kg · cm/cm; however, its rigidity and tensile strength were inferior to those of PP/LDPE/block copolymer blend.     

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     

Rheological,mechanical and thermal properties of propylene‐ethylene block copolymer/polyalphaolefins blends

The rheological, thermal, and mechanical properties of propylene–ethylene block copolymer (PPB) blends with predominantly atactic molecular structure of low molecular weight polypropylene and propylene copolymers with either ethylene or 1‐butene (APAO) have been studied. It has been found that blend properties depend on comonomer type, content, and molecular weight of APAO as well as blend composition. APAO having ethylene comonomer showed better miscibility with PPB than the other ones, and high comonomer content of APAOs gave dramatic increase in impact strength over 30 wt%. It has been concluded that APAO can be used as an effective modifier of PPB. POLYM. ENG. SCI., 47:1905–1911, 2007. © 2007 Society of Plastics Engineers     

Glass transition of undrawn and drawn copolyetherester thermoplastic elastomers

The phase and deformation behaviour of two types of copolyetheresters (the block copolymers E and P) were studied by means of DSC, dynamic mechanical spectroscopy and X-ray diffraction. The block copolymers E and P based on poly(butylene therephtalate) (PBT) as a hard block have poly(tetramethylene oxide) (PTMO) and triblock copolymer (PEO-PPO-PEO) with a middle poly(propylene oxide) (PPO) block and two end poly(ethylene oxide) (PEO) as a soft block, respectively. The complex investigation shows that the studied copolyetheresters are microphase separated polymer systems in the amorphous matrix of which the PBT crystallites are embedded. The volume fraction of PBT crystallites depends on the block copolymer composition and changes from 5 to 20%. In the amorphous matrix that is the mixed PBT/ the soft block phase the soft block acts as a PBT plasticizer reducing the glass transition temperature of the amorphous mixed phase. The most interesting aspect of the phase behaviour of the copolyetheresters consists in the fact that, in comparison with PTMO, the triblock is characterized by a more pronounced PBT plasticization effect. A special emphasis was placed in this work on the investigation of an increased glass transition temperature of drawn copolyetheresters. It was found that this process depends on the volume fraction of PBT crystallites and chemical structure of the soft blocks. The first factor characterizes the interaction between the amorphous mixed phase and PBT crystallites and, therefore, the higher value of the volume fraction of PBT crystallites the higher is the glass transition temperature of drawn copolyetheresters. The second factor determines the PBT plasticization effect of the soft blocks and a level of the interaction of chains in the amorphous mixed phase. Because of a weaker PBT plasticization effect of PTMO in comparison with that of the triblock, the deformation of the block copolymer E is accompanied by a more pronounced elevation of the glass transition temperature in comparison with the block copolymer P.     

Dynamic mechanical properties and morphology of polypropylene block copolymers and polypropylene/elastomer blends

The relation between the dynamic mechanical properties and the morphology of polypropylene (PP) block copolymers and polypropylene/elastomer blends was studied by dynamic mechanical analysis (DMA), light- and electron microscopy. The latter techniques contributed to an improvement in assignments of relaxation transitions in the DMA spectra. It was established that PP block copolymers had multiphase structure since the ethylene/propylene rubber phase (EPR) formed in the copolymerization contained polyethylene (PE) domains. An identical morphology was found in the case of PP/polyolefin thermoplastic rubber (TPO) blends. Impact modification of PP by styrene/butadiene block copolymers led to a multiphase structure, too, due to the polystyrene (PS) domains aggregated in the soft rubbery polybutadiene phase. In the semicrystalline polyolefinic and in the amorphous styrene/butadienebased thermoplastic rubbers, PE crystallites and PS do mains acted as nodes of the physical network structure, respectively. PP/EPDM/TPO ternary blends developed for replacing high-density PE showed very high dispersion of the modifiers as compared to that of PP block copolymers. This fine dispersion of the impact modifier is a basic regulating factor of impact energy dissipation in the form of shear yielding and crazing.     

Crystallization,melting behavior,and morphology of BPP/HDPE blend

The crystallization, melting behavior, and morphology of a low ethylene content block propylene–ethylene copolymer (BPP) and a high-density polyethylene (HDPE) blend were studied. It was found that the existence of ethylene–propylene rubber (EPR) in BPP has more influence on the crystallization of HDPE than on that of PP. This leads to the decreasing of the melting temperature of the HDPE component in the blends. It is suggested that the EPR component in BPP shifted to the HDPE component during the blending process. The crystallinity of the HDPE phase in the blends decreased with increasing BPP content. The morphology of these blends was studied by polarized light microscopy (PLM) and SEM. For a BPP-rich blend, it was observed that the HDPE phase formed particles dispersed in the PP matrix. The amorphous EPR chains may penetrate into HDPE particles to form a transition layer. © 1998 John Wiley & Sons, Inc. J. Appl. Polym. Sci. 69: 2469–2475, 1998