Ethylene-propylene Segmented Copolymer Research Articles

Crystallization behavior of impact copolymer polypropylene revealed by fast scanning chip calorimetry analysis

The crystallization behaviors of two impact copolymer polypropylenes (ICP) were investigated by using fast scanning chip calorimetry (FSC) and micro-focus wide-angle X-ray diffraction (WAXD) techniques. Different crystallization peaks of these two samples during cooling were observed at cooling rates from 50 to 4000 K/s. For ICP-A, the crystallization of polypropylene (PP) matrix into α crystallites, polyethylene (PE) sequences in ethylene-propylene segmented copolymer (EsP), PP segments in ethylene-propylene block copolymer (EbP), and PP matrix into mesophase successively occurred from high to low temperatures. As the cooling rate increased, the crystallization of PP matrix into α crystallites, PP segments, and mesophase were suppressed one by one. Nevertheless, the crystallization of PE segments was hardly suppressed. For ICP-B, it showed almost the same crystallization behavior as ICP-A, except for the absence of independent crystallization peak of PP segments. The different crystallization performance in these two samples could be ascribed to their different chain microstructures.

Analysis of Defects in Biaxially Oriented Polypropylene Films by Micro-Fourier Transform Infrared and Raman Spectroscopies

Abstract A practical method for identification of defects that occur occasionally during the production of biaxial oriented polypropylene (BOPP) films is developed. The size and morphology of the defects in the BOPP film were observed with optical microscopy, and micro Fourier transform infrared (Micro-FTIR) and Raman spectroscopies were employed to identify the chemical composition of the defects. Significant amounts of ethylene and propylene units were found in the defects, and characteristic vibrational bands for crystalline PP were observed by both IR and Raman. However, one defect exhibited IR characteristics for ordered PE whereas the other showed amorphous PE structure. These results indicate that the defects are composed of either ethylene-propylene block copolymers with long sequences of both propylene and ethylene that can form ordered structures, or ethylene-propylene segmented copolymers with long propylene sequences that can crystallize and shorter ethylene sequences that are amorphous. Possible sources of these foreign materials and corresponding mitigation measures were discussed.

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).

Ethylene–Propylene Segmented Copolymer as an in Situ Compatibilizer for Impact Polypropylene Copolymer: An Assessment of Rheology and Morphology

This work aims to probe the roles of ethylene–propylene segmented copolymer (EPS) in impact polypropylene copolymers (IPCs) by rheological and morphological investigations. A series of IPCs with different EPS contents and molecular structures are prepared by an atmosphere-switching polymerization process (ASPP). The Palierne emulsion model is used to describe the relationship between the rheological response to small amplitude oscillatory deformation and the morphology of IPC. It is found that this model describes well the linear viscoelastic responses of IPC, if the role of EPS is taken into account. An increase in the content of EPS and the length of its PP segments leads to a decrease in the size of the ethylene–propylene random copolymer (EPR) phase domains and the interfacial tension. These results strongly confirm the role of the EPS as a compatibilizer in the IPC system. The adhesion between the PP matrix and the EPR phase domains is enhanced by the presence of the EPS that is produced in situ duri...

A model for the structures of impact polypropylene copolymers produced by an atmosphere-switching polymerization process

This work reports on the development of a model to establish the relationship between the structures of impact polypropylene copolymer (IPC), a high performance polymer material, and the characteristics of an atmosphere-switching polymerization process (ASPP), a new polymerization route. To calculate the complex structures of IPC, a detailed kinetic mechanism was proposed to describe the kinetic behavior of the active centers of Ziegler–Natta catalyst during ASPP. The semibatch ASPP for synthesizing IPC was carried out for the model validation. The model is capable of predicting the evolution of the compositional distributions of IPC as a function of switching frequency (SF), which is the main characteristic parameter of ASPP. ASPP not only allows controlling the contents of ethylene–propylene random copolymers (EPR) and ethylene–propylene segmented copolymers (EPS,) but also tuning the composition of EPS. Other applications of the model are discussed.

Characterization of the microstructure of impact polypropylene alloys by preparative temperature rising elution fractionation

Two polypropylene alloys (Samples A and B), as impact polypropylene (PP) with similar ethylene contents and melt indices but different impact properties at low temperatures, are fractionated into eight fractions using preparative temperature rising elution fractionation. The microstructure of the original samples and their fractions are studied using high-temperature gel permeation chromatography, Fourier transform infrared spectroscopy, 13C nuclear magnetic resonance spectroscopy, and differential scanning calorimetry. The results indicate that the two alloys are mainly composed of four portions: ethylene–propylene random copolymer (EPR), ethylene–propylene segmented copolymer, ethylene–propylene block copolymer, and propylene homopolymer. Sample A contains more EPR and more fractions with higher isotacticity eluted at 120 and 140 °C than Sample B. The difference in the microstructure distributions of both PP alloys results in observable differences in their mechanical properties: Sample A has better impact toughness and possesses higher rigidity than Sample B. Sample A also exhibits better balance between toughness and stiffness.

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

AbstractA 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

New polypropylene blends toughened by polypropylene/poly(ethylene-co-propylene) in-reactor alloy: Compositional and morphological influence on mechanical properties

Abstract A new toughening agent, polypropylene/poly(ethylene-co-propylene) in-reactor alloy (EP-P), has been adopted to modify isotactic polypropylene (PP) in present study. Systematic investigation has been performed on the inter-compositional interaction, crystalline structure, and phase morphology of a series of PP/EP-P blends. It has been found that the PP component from EP-P is thoroughly miscible with neat PP and they together serve as the matrix of the PP/EP-P blends, while the ethylene–propylene random copolymers (EPR) act as the dispersed phase. The ethylene–propylene segmented copolymers (EPS), behaving as the compatibilizer between the EPR dispersed phase and PP matrix, strengthen mutual incorporation and effective diffusion of the amorphous PP segments and the EPR molecules. Based on the in-depth understanding of the crystalline structure and phase morphology, the correlation between morphological structure and mechanical properties has been established. The excellent impact toughness of PP/EP-P blends with higher EP-P content is mainly attributed to the small PP crystallites scattered in the blends and the well dispersed EP copolymer domains in PP matrix.

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

AbstractFour 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

Influence of the reaction conditions on the solid‐state graft copolymerization of methyl methacrylate and polyethylene/polypropylene in situ alloys

AbstractGraft copolymers of poly(methyl methacrylate) (PMMA) with spherical, high‐porosity polyethylene (PE)/polypropylene (PP) in situ alloys were synthesized by a solid‐state reaction. The effects of the amount of the free‐radical initiator, the feed ratio of the methyl methacrylate (MMA) monomer, the reaction temperature, and the composition of the alloys on the grafting degree of PMMA were studied. A greater amount of the initiator and a higher reaction temperature led to a higher grafting degree. The grafting degree first increased with the feed ratio of MMA but leveled off at a higher feed ratio. The obtained graft copolymer was fractionated by temperature gradient extraction fractionation into six fractions, and each fraction was characterized by Fourier transform infrared and differential scanning calorimetry. The structures of these fractions were ungrafted ethylene–propylene random copolymers and ethylene–propylene segmented copolymers, ethylene–propylene block copolymers having PE and PP segments of different lengths and grafted by PMMA, PP grafted by PMMA, and nearly pure PP. Most PMMA was grafted on propylene segments, and thus the grafting degree decreased as the content of ethylene units in the alloys increased. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 98: 195–202, 2005

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

AbstractTwo 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

Phase morphology and impact toughness of impact polypropylene copolymer

Factors influencing the impact toughness of two impact polypropylene copolymers (IPC) with almost the same ethylene content, molecular weight and molecular weight distribution were studied by temperature gradient extraction fractionation (TGEF), scanning electron microscopy (SEM), nuclear magnetic resonance (NMR) and differential scanning calorimetry (DSC). The results indicate that poor interfacial adhesion between the disperse phase and the continuous matrix, larger dimensions and non-uniform distribution of disperse phases are main reasons for the low impact toughness of IPC B that possesses of a low content of ethylene–propylene segmented copolymer with long crystallizable PE and PP sequences as a compatibilizer between the disperse phase and the matrix.

Structure and properties of impact copolymer polypropylene. II. Phase structure and crystalline morphology

In this work, an impact copolymer polypropylene (ICPP) was separated into 4 fractions, A, B, C, and D. The phase structure, thermal behavior, and crystalline morphology of the ICPP and its 4 fractions were studied thoroughly using scanning electron microscopy (SEM). Dynamic mechanical analysis (DMA), differential scanning calorimetry (DSC), and polarized light microscopy (PLM). Results of SEM and DMA show that ethylene–propylene rubber (EPR) and part of the ethylene–propylene segmented copolymer disperse as toughening particles in the ICPP. The size and size distribution of these particles are determined by chain structure of the fractions of ICPP. From fraction A to fraction D, the morphology changes from noncrystalline to semicrystalline gradually, as shown by DSC. DSC results also indicate that thermal behavior of the ICPP agrees greatly with its chain structure. PLM demonstrates that it is difficult for the ICPP to grow perfect spherulites, that is, partially, because the matrix of ICPP, fraction D, has defects in its macromolecular chain. Another cause is that there is a good compatible structure in the ICPP and so the noncrystalline component (including all fractions) hinders the growth of the spherulite. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 71: 103–113, 1999