Amorphous Ethylene-propylene Copolymer Research Articles

Polyethylene/crystalline ethylene-propylene copolymer/amorphous ethylene-propylene copolymer in-reactor alloys synthesized by periodic switching polymerization process: An excellent toughener for polypropylene

In order to obtain softer polyolefins applicable as toughener for polypropylene (PP), a series of in-reactor alloys composed of polyethylene, crystalline ethylene-propylene copolymer (cEP) and amorphous ethylene-propylene copolymer (aEP) were synthesized by sequential ethylene polymerization followed by ethylene-propylene copolymerization in periodic switching polymerization process (PSPP) using a spherical MgCl2-supported Ziegler-Natta catalyst. In the PSPP step, ethylene-propylene copolymerization was repeatedly switched between two different monomer feed ratios: one with high propylene/ethylene ratio to form aEP component, and the other with low propylene/ethylene ratio to form cEP component. In the synthesized PE/cEP/aEP in-reactor alloys, aEP accounted for 40~56 wt%, and cEP accounted for 18~30 wt% of the alloy. With aEP content rising above 48 wt%, the alloys showed rather low modulus, and no yielding appeared in their stress–strain curve, implying that they were a sort of elastomeric material. By blending the PE/cEP/aEP alloys with isotactic PP, their PP-toughening performances were evaluated and compared with a commercial EPDM. Impact strength of PP toughened by the alloy was significantly higher than that toughened by EPDM at the same blend ratio. Cryo-fractured surface of PP/alloy blends showed that the alloy particles were uniformly dispersed in PP matrix, and showed a core–shell type morphology, in which the core domain was composed of polyethylene, and aEP constituted the shell domain in between the core and the PP matrix. Segmented EP copolymer chains (s-EP) located inside the aEP domains formed thin filaments bridging the core and the PP matrix, which are believed to act as compatibilizer that significantly enhanced interfacial adhesion between the PP matrix and the dispersed phase.

Characterization of phase morphology of polymer melts (PP/PE blends) via rheology

AbstractThe viscoelastic behavior of high impact polypropylene (PP) melts, a multiphase system with an isotactic PP matrix and inclusions consisting of mainly amorphous ethylene–propylene copolymer (EP), is strongly influenced by the size of small inclusions. The dynamic moduli of such two‐phase systems (reactor products) are well described by Palierne's emulsion model. For this analysis the reactor product is separated into matrix and dispersed phase via the different solubility in xylene. This analysis also provides information on the ratio interfacial tension to particle size of the dispersed phase. With morphology data (particle size) of the solidified heterophasic samples (Transmission Electron Microscopy), we estimate the interfacial tension between PP and EP copolymer via the emulsion model of Palierne and from the relaxation time spectra according to Gramespacher and Meissner. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2007

FI catalysts: new olefin polymerization catalysts for the creation of value-added polymers.

This contribution reports the discovery and application of phenoxy-imine-based catalysts for olefin polymerization. Ligand-oriented catalyst design research has led to the discovery of remarkably active ethylene polymerization catalysts (FI Catalysts), which are based on electronically flexible phenoxy-imine chelate ligands combined with early transition metals. Upon activation with appropriate cocatalysts, FI Catalysts can exhibit unique polymerization catalysis (e.g., precise control of product molecular weights, highly isospecific and syndiospecific propylene polymerization, regio-irregular polymerization of higher alpha-olefins, highly controlled living polymerization of both ethylene and propylene at elevated temperatures, and precise control over polymer morphology) and thus provide extraordinary opportunities for the syntheses of value-added polymers with distinctive architectural characteristics. Many of the polymers that are available via the use of FI Catalysts were previously inaccessible through other means of polymerization. For example, FI Catalysts can form vinyl-terminated low molecular weight polyethylenes, ultra-high molecular weight amorphous ethylene-propylene copolymers and atactic polypropylenes, highly isotactic and syndiotactic polypropylenes with exceptionally high peak melting temperatures, well-defined and controlled multimodal polyethylenes, and high molecular weight regio-irregular poly(higher alpha-olefin)s. In addition, FI Catalysts combined with MgCl(2)-based compounds can produce polymers that exhibit desirable morphological features (e.g., very high bulk density polyethylenes and highly controlled particle-size polyethylenes) that are difficult to obtain with conventionally supported catalysts. In addition, FI Catalysts are capable of creating a large variety of living-polymerization-based polymers, including terminally functionalized polymers and block copolymers from ethylene, propylene, and higher alpha-olefins. Furthermore, some of the FI Catalysts can furnish living-polymerization-based polymers catalytically by combination with appropriate chain transfer agents. Therefore, the development of FI Catalysts has enabled some crucial advances in the fields of polymerization catalysis and polymer syntheses.

Dispersed phase morphology of impact PP copolymers. Effects of blend composition as determined by TREF

AbstractPolypropylene (PP) blends, commercially known as “impact polypropylene copolymers” (IPC), are produced by a sequential gas phase polymerization process. The final product is a complex mixture of polypropylene (PP) and a range of ethylenepropylene copolymers (EPC) with different ethylene contents. In the present work, the composition of three different IPC was estimated by performing a step elution mode Analytical Temperature Rising Elution Fractionation (TREF) separation. The recovered fractions were analyzed by Differential Scanning Calorimetry (DSC), Size Exclusion Chromatography (SEC) and Fourier Transform Infrared Spectroscopy (FTIR). The morphology was examined by Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Amorphous EPC were isolated in an independent way in order to perform a more careful characterization. The distinct particle size and shape of the dispersed phase for different IPC was interpreted in terms of the molecular characteristics of the blend components and their compositions.

Sequence distributions versus catalyst site behavior of in situ blends of polypropylene and poly(ethylene-co-propylene)

Sequential polymerizations of first propylene and then ethylene, propylene mixtures with the same Ziegler-Natta catalyst system produce in situ blends known as high-impact polypropylenes. Over 100 high-impact polypropylenes are characterized in terms of weight fractions and sequence distributions for isotactic polypropylene, atactic polypropylene, an amorphous ethylene propylene copolymer, and a crystalline ethylene propylene copolymer. The apparent r 1 r 2 behaviors of the E/P copolymers suggest that the amorphous and crystalline E/P copolymers principally arise from different types of catalyst sites as opposed to originating strictly from compositional heterogeneities. The amorphous copolymers consistently have r 1 r 2 values close to unity over a broad range of compositions, while the corresponding crystalline copolymers have apparent r 1 r 2 values that range from 2 to over 20. An apparent r 1 r 2 close to unity not only reflects random sequencing but also indicates a narrow compositional distribution. This r 1 r 2 result indicates that the amorphous E/P copolymers are produced from a singular type of catalyst site. The higher r 1 r 2 values shown by the crystalline E/P copolymers indicate broad compositional distributions that are produced by a different type or types of catalyst sites. The ratio of amorphous to crystalline ethylene, propylene copolymers is nominally around 80/20 over a broad range of impact copolymer compositions. The consistency of this result suggests that the two basic types of catalyst sites producing E/P copolymers are also in an approximate 80/20 ratio.

Sequence distributions versus catalyst site behavior of in situ blends of polypropylene and poly(ethylene‐co‐propylene)

Sequential polymerizations of first propylene and then ethylene, propylene mixtures with the same Ziegler–Natta catalyst system produce in situ blends known as high-impact polypropylenes. Over 100 high-impact polypropylenes are characterized in terms of weight fractions and sequence distributions for isotactic polypropylene, atactic polypropylene, an amorphous ethylene propylene copolymer, and a crystalline ethylene propylene copolymer. The apparent r1r2 behaviors of the E/P copolymers suggest that the amorphous and crystalline E/P copolymers principally arise from different types of catalyst sites as opposed to originating strictly from compositional heterogeneities. The amorphous copolymers consistently have r1r2 values close to unity over a broad range of compositions, while the corresponding crystalline copolymers have apparent r1r2 values that range from 2 to over 20. An apparent r1r2 close to unity not only reflects random sequencing but also indicates a narrow compositional distribution. This r1r2 result indicates that the amorphous E/P copolymers are produced from a singular type of catalyst site. The higher r1r2 values shown by the crystalline E/P copolymers indicate broad compositional distributions that are produced by a different type or types of catalyst sites. The ratio of amorphous to crystalline ethylene, propylene copolymers is nominally around 80/20 over a broad range of impact copolymer compositions. The consistency of this result suggests that the two basic types of catalyst sites producing E/P copolymers are also in an approximate 80/20 ratio. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1527–1542, 1998

Evaluation of X-ray-excited Valence Band Measurements for the Determination of the Surface Composition of Model Thermoplastic Olefins

In this study we evaluate the utility of using x-ray-excited valence band measurements for the determination of the surface composition of simple model thermoplastic olefin systems composed of binary blends of semicrystalline polypropylene (PP) and an amorphous ethylene–propylene copolymer (E-co-P). Blend compositions included combinations of high- and low-molecular-weight (MW) PP and E-co-P composed of 60 wt.% PP/40 wt.% E-co-P and 80 wt.% PP/20 wt.% E-co-P blends. Results demonstrate that experimental valence band spectra for the polyolefin blends can be approximated by a linear combination of the pure-component valence band spectra. Bulk compositions determined from spectra recorded from cryomicrotomed cross-sections were found to be consistent with the bulk component wt.%. The surface compositions of the binary blends were all found to be enriched in PP. Measurements taken from the 60/40 wt.% blends were 10–20% higher in PP concentration than the bulk compositions, and were found to vary depending on the MW combination of the components. No MW dependence was observed for the 80/20 wt.% blends, apparently due to a near saturation of the surface with PP. The development of methods for assessing the surface composition of these types of materials may prove useful in monitoring changes in composition with material formulation and process conditions. Information of this nature could be helpful in permitting an evaluation of potential influences of composition on adhesion. © 1997 by John Wiley & Sons, Ltd

Composition and Crystallinity Effects in the Degradation of Ethylene-Propylene Copolymers by γ-Radiation

Abstract The degradation by γ-radiation of amorphous ethylene-propylene (EP) copolymers containing 23 and 36% propylene has been studied by measuring the yields of radical intermediates (at 77 K), volatile products (H, and CH, at 300 K), and main-chain scission and crosslinking. The G values for these changes in the homopolymers polyethylene (PE) and polypropylene (PP) all increase with decreasing crystallinity. The values for the amorphous EP copolymers are much lower than would be predicted by linear extrapolation of the values for PE and PP of low crystallinity. We conclude that all of these radiation-induced chemical changes in polyolefins occur preferentially at crystalline surfaces and defects; consequently the G values will be lower for both highly crystalline and amorphous polymers than for polymers of low crystallinity.

Radiation effects of paraffins as polymer model compounds—I. Evolved gas analysis

Radiation yields of gases from n-paraffins of n-C 20H 42 to n-C 24H 50 and squalane (C 30H 62), as polymer model compounds, in the liquid and solid phases were analyzed by gas chromatography. G(H 2) in the liquid phase was 3.2–3.3 for all samples and found to be almost independent of the chemical structure and molecular weight; G(H 2) in the crystalline state of n-paraffins was 2.2–2.5 at -77 to 25°C. G(CH 4) was about 1% of G(H 2) for n-paraffins and increased with the methyl content of the branched chain for squalane. G(C 2H 6) in the liquid phase was about 0.05 for n-paraffins, but G(C 2H 6) in the crystalline state was found to depend on the crystal structure; that is, nearly zero for triclinic of an even number of carbons and about 0.02 for orthorhombic of an odd number. C 3H 8 and C 2H 4(C 3H 6 in squalane) were observed only in the liquid phase of n-paraffins and in glass and the liquid phase of squalane; G(C 3H 8) = 0.03–0.05 and G(C 2H 4 or C 3H 6) = 0.01–0.03. But the C 4-compounds were not detected in any phase of any of the samples. Chain scission by radiation is supposed to proceed mainly at chain end carbons until the third carbon in the liquid phase of n-paraffins, only at the chain end carbon of the crystalline surface in triclinic crystals and at chain end carbons until the second carbon in orthorhombic crystals. These chain scission phenomena in the liquid phase and crystalline state of n-paraffins and in the liquid phase of squalane would be analogous to those in the amorphous and crystalline states of polyethylene, and in amorphous ethylene-propylene copolymer, respectively.

Effect of absorbing pigments on the photo-oxidation and mechanical property changes in ethylene-propylene copolymers

The present paper reports observations on the ZnO and TiO 2 photo-catalyzed oxidations of an amorphous ethylene-propylene copolymer containing 75% w/w of ethylene. Hydroperoxide and carbonyl group formation occurs with subsequent changes in the mechanical properties. Differences between ZnO and TiO 2 are observed particularly in the hydroperoxidation processes. A reinforcing effect due to the photo-active pigments can account for the differences in mechanical properties, even at high carbonyl content.

The radiation crosslinking and scission of ethylene‐propylene copolymers studied by solid‐state nuclear magnetic resonance

AbstractMethyl groups from chain scission and H‐crosslinks have been identified by solid‐state nuclear magnetic resonance in amorphous ethylene‐propylene copolymers containing 23 and 36 mole % propylene after γ‐irradiation to 10 MGy at 30°C. G (scission) and G (crosslink) values determined from the n.m.r. spectra and by extraction are in agreement, which suggests that the crosslinks are not clustered. This may differ from the situation in polyethylene where there is a substantial crystalline content. G(S). G(X) and the ratio G(S)/G(X) increase with increasing propylene content of the copolymers.

New Trends in the Field of Propylene Based Polymers

This paper deals with the high degree of control of the intimate structure of polymers obtained with Ziegler–Natta (Z-N) catalysts. In the field of the poly(α-olefin)s, there are Z-N catalysts able to produce high density polyethylene, isotactic polypropylene (PP) or ethylene–propylene (EP)-copolymers including the EP-elastomers. The heterophasic phenomena and in particular the toughening of PP with amorphous ethylene–propylene copolymers have been studied. By terpolymerization of propylene, ethylene and other monomer such as 1-butene, terpolymers with very interesting performance are produced, thanks to the addition of 1-butene to ethylene–propylene copolymers. A decrease in Tgδ takes place in raw polymers, while polyethylene crystallinity is found at higher ethylene content than is the corresponding ethylene–propylene copolymers. An increase in tensile strength and a decrease in permanent deformation is noticed, both at environment and low temperature for the vulcanized products compared to the traditional ethylene–propylene copolymers. By the use of the above catalysts, copolymers and saturated terpolymers free from low volatile substance may be produced. Production of these new copolymers and saturated terpolymers can be carried out by highly simplified processes, mainly consisting of a polymerization and a monomer flashing step only, and the well known advantages have already been achieved with the new processes for the production of poly(α-olefin)s.

Fine structure in spectra of internal friction and the character of relaxation transitions in amorphous ethylene-propylene copolymer

Fine structure has been revealed in spectra of internal friction of amorphous ethylene-propylene elastomer SKEP-30 by means of three dynamic methods. The fine structure in the relaxation spectrum of the same material, calculated from long-time isothermal stress relaxation experiments, was also investigated. Results of all methods are in agreement and together give evidence that four groups of relaxation transition (β-, α-, λ, and δ-groups) are characteristic for SKEP-30 in the interval between 100 K and the temperature of thermal decomposition. The most rapid (β) as well as the most slow (δ) of the four are short-range, very local processes that pertain to kinetic units consisting of atoms or monomeric links in the polymer chain. The group of α-transitions is related to segmental mobility while the group of λ-processes is connected with the life-span of physical crosslinks in the molecular network. Splitting of β- and α-transitions indicates that two amorphous structures exist in SKEP-30.

Aging and degradation of polyolefins. III. Polyethylene and ethylene–propylene copolymers

AbstractRates of oxygen absorption and formation of oxidation products were determined in γ‐initiated oxidations of thin films of high‐ and low‐density polyethylene, atactic and isotactic polypropylene, and of three ethylene–propylene copolymers. Radiation yields G for O2 absorbed and formation of hydroperoxides depend on dose rates and decrease sharply with increasing ethylene content of the copolymers and moderately with increasing crystallinity of any base polymer. G values for dialkyl peroxide and carbonyl formation, and therefore for chain initiation and termination, do not change much with polymer composition and crystallinity and not at all with dose rates. A few experiments with atactic polypropylene and an amorphous ethylene–propylene copolymer, initiated by di‐tert‐butylperoxy oxalate, indicate that 37 mole‐% of ethylene in the polymer increases the efficiency of initiation and the tendency toward crosslinking.