EP Copolymers Research Articles

New approaches to characterize polymeric oil additives in solution based on pyrene excimer fluorescence

Maleated polyolefins (MaPOs) such as maleated ethylene propylene copolymers or polyisobutylene terminated at one end with a succininic anhydride can be used as polymeric dispersants in engine oils after reaction with polyamines while unmodified EP copolymers improve the viscosity index of oils. MaPOs can also be labeled with pyrene derivatives to generate pyrene-labeled polyolefins (PyLPOs) as fluorescent mimics of oil additives and pyrene excimer fluorescence (PEF) can be applied to probe their behavior in solution. This review describes new methodology that was recently implemented to characterize the complex fluorescence signal emitted by PyLPOs by using steady-state and time-resolved fluorescence. This methodology enables one to gain quantitative information about the level of clustering of the succinic pendants along a maleated polyolefins and intra- and intermolecular aggregation of polyolefins in solution. Such information is relevant to scientists aiming to characterize polymeric oil additives used in engine oil. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 7–18

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.

Fractionation and Characterization of Impact Poly(propylene) Copolymers by High Temperature Two‐Dimensional Liquid Chromatography

SummaryInformation regarding molar mass distribution (MMD) and chemical composition distribution (CCD) of complex polyolefins such as impact polypropylene copolymer (IPC) is important in order to fully understand their properties during processing and application. Precise analysis of such polymeric materials having multiple distributions in various molecular characteristics is a difficult task and single separation methods fail to provide enough information about their microstructure. Preparative fractionation and subsequent analysis of the separated fractions was found to be an effective method for their complete characterisation. In this work, a combination of preparative TREF with high temperature two‐dimensional liquid chromatography was used for the separation and analysis of the complex components in a commercial IPC sample. In addition to the ethylene‐propylene (block or segmented) copolymers and low molar mass isotactic polypropylene (iPP) homopolymer (as expected in the semicrystalline TREF fraction of an IPC), significant amounts of high molar mass iPP and polyethylene (PE) homopolymer were observed. The results showed that the TREF‐HT‐2D‐LC combination can be used as a powerful analytical tool for the complete microstructural analysis of such complex EP copolymers.

Thermal fractionation and effect of comonomer distribution on the crystal structure of ethylene–propylene copolymers

In this paper the comonomer distributions of two series of ethylene–propylene copolymers with different propylene contents, which were prepared by a fluorinated bis(phenoxyimine) Ti catalyst (FI–EP copolymers) and a conventional Ziegler–Natta catalyst (ZN–EP copolymers), respectively, were characterized. It is found that the comonomer distribution of ethylene–propylene copolymers can still be characterized by thermal fractionation at a long scale, though the propylene units can be incorporated into the PE crystal lattice. The FI–EP copolymers exhibit a narrow and random comonomer distribution, whereas a broad comonomer distribution is observed for the ZN–EP copolymers. The crystal structures of the FI–EP and ZN–EP copolymers were studied by WAXD. The a-axis of the PE crystals of the FI–EP copolymers increases rapidly with propylene content, indicating that more propylene units are incorporated into the PE crystal lattice, whereas only a slight expansion in a-axis is observed for the ZN–EP copolymers. WAXD result also shows the presence of hexagonal phase in the FI–EP copolymers and the relative content of the hexagonal phase increases with the propylene content, while in the ZN–EP copolymers the hexagonal phase is negligible.

Evolution of phase morphology of high impact polypropylene particles upon thermal treatment

Solvent fractionation and differential scanning calorimetry (DSC) results show that high impact polypropylene (hiPP) produced by a multistage polymerization process consists of PP homopolymer, amorphous ethylene–propylene random copolymer (EPR), and semicrystalline ethylene–propylene copolymer. For the original hiPP particles obtained right after polymerization, direct transmission electron microscopy (TEM) observation reveals a fairly homogeneous morphology of the ethylene–propylene copolymer (EP) phase regions inside, while the polyethylene-rich interfacial layer observed between the EP region and the iPP matrix supports that EP copolymers form on the subglobule surface of the original iPP particles. Compared with that in original hiPP particles, the dispersed EP domains in pellets have much smaller average size and relatively uniform size distribution, indicating homogenization of the EP domains in the hiPP by melt-compounding. Upon heat-treatment, phase reorganization occurs in hiPP, and the dispersed EP domains can form a multiple-layered core–shell structure, comprising a polyethylene-rich core, an EPR intermediate layer and an outer shell formed by EP block copolymer, which accounts to some extent for the good toughness-rigidity balance of the material. The results indicate that to establish the optimum phase structure and desired properties for hiPP, both the architecture of original hiPP particles and subsequent melt-processing conditions should be carefully modulated.

The role of microstructure, molar mass and morphology on local relaxations in isotactic polypropylene. The α relaxation

This study aims to assess the relative influence of microstructure, molar mass and morphology on the local α relaxation of isotactic polypropylene (iPP). For that purpose, three families of samples have been prepared. The Ziegler–Natta type provides a wide molar mass range where both the isotactic average length (n1) and the nature of the isotacticity interruptions change according to chain size. The metallocene type allows to analyse also the samples in which molar mass and n1 are related but the nature of the defects stays the same. Finally, three propylene-like EP copolymers (containing only isolated ethylene units) have been synthesised via metallocene catalysis in order to study samples which combine both relatively high molar masses and short n1.Among the factors considered, microstructure and n1 in particular have been found to drive mainly the quality of the α relaxation. Concerning the intensity, it has been observed that some microstructural features related to n1 must be fulfilled for this dynamics to take place. Provided this requirements are met, the intensity of the α relaxation depends on the final crystalline distribution resulting from a given molar mass, microstructure and processing conditions.

Morphology and mechanical properties in the binary blends of isotactic polypropylene and novel propylene-co-olefin random copolymers with isotactic propylene sequence 1. Ethylene–propylene copolymers

The additive effects of the novel ethylene–propylene random (EP) copolymers with high isotacticity in propylene sequence on the morphology and mechanical properties of isotactic polypropylene (iPP) were investigated using polarized optical microscopy, transmission electron microscopy, dynamic mechanical analysis and tensile behavior. According to these results, the EP copolymers with a propylene content of more than 84mol% were miscible with iPP, in which the crystallizable PP sequences in these EP copolymers were incorporated in crystal lattice of iPP and the other portions in the EP chains were excluded to the amorphous phases. Consequently, they act as tie molecules linking between adjacent lamellae, leading to enhancement of yield toughness of iPP. On the other hand, the EP copolymers with a propylene-unit content of less than 77mol% were incompatible with iPP. The iPP/EP blends showed the phase-separated morphology.

Blends of propylene-ethylene and propylene-1-butene random copolymers: I. Morphology and structure

Samples of propylene-ethylene (EP) and propylene-(1-butene) (BP) random copolymers with various comonomer content (2–3.1wt% ethylene, 9.9wt% 1-butene), were melt-mixed in Brabender internal mixer at various compositions (25/75, 50/50, 75/25). Films of copolymers and blends, as well as of a homopolymer sample (iPP), obtained by compression moulding and with different thermal history were characterized by optical and scanning electron microscopy (OM, SEM), small-angle light scattering (SALS), small- and wide angle X-ray scattering (SAXS, WAXS) and differential scanning calorimetry (DSC). It was found that all copolymers and blends studied crystallized exclusively in monoclinic α-modification forming spherulitic structure in a very broad undercooling range. The average size of spherulites is smaller in the copolymer containing 1-butene as compared to those containing ethylene or to iPP homopolymer, due to enhanced heterogeneous nucleation in BP copolymer. SEM microscopic observations demonstrated that EP and BP copolymers were miscible at all examined compositions and form homogeneous blends. Structural and morphological analysis indicated that the comonomer units are incorporated into growing crystallites in both EP and BP copolymers, while the non-crystallizing material is rejected out of the crystallites. For small concentrations of comonomer some of non-crystallizing species are pushed ahead of the front of growing spherulite into interspherulitic regions. For higher comonomer concentration these species are mostly trapped in intraspherulitic regions. Melting behavior of copolymers reflects the incorporation of comonomer into crystalline phase: melting temperature and crystallinity degree decrease in copolymers and blends as compared to plain iPP.

Modeling branched polyethylene: copolymers possessing precisely placed ethyl branches.

A structural investigation of precise ethylene/1-butene (EB) copolymers has been completed using step polymerization chemistry. The synthetic methodology needed to generate four model copolymers is described; their primary and higher level structure is characterized. The copolymers possess an ethyl branch on every 9th, 15th, and 21st carbon along the backbone of linear polyethylene. Melting points and heats of fusion decrease with increased branch frequency. Differential scanning calorimetry and infrared spectroscopy show highly disordered crystal structures favoring ethyl branch inclusion. On the other hand, the EB copolymers contain high concentrations of kink and gauche defects independent of branch frequency. These model copolymers are compared with random copolymers produced using traditional chain chemistry and previously synthesized ADMET EP copolymers.

Surface damage behavior during scratch deformation of mineral reinforced polymer composites

The surface damage behavior during scratch deformation of neat and wollastonite reinforced ethylene–propylene and polypropylene polymeric materials with significant differences in ductility was studied using electron microscopy in association with scratch deformation parameters and local crystallinity characteristics obtained from atomic force microscopy. Under identical conditions of scratch tests, the decrease in resistance to scratch damage and stress whitening of polymeric materials followed the sequence: wollastonite-reinforced polypropylene (PP-W) ≅ wollastonite-reinforced ethylene–propylene (EP-W) > neat polypropylene (PP) > neat ethylene–propylene copolymer (EP). The improved resistance to scratch damage of mineral reinforced polymeric materials is attributed to the effective reinforcement by micrometer-sized wollastonite particles that increase the tensile modulus of the polymeric materials and restrict plastic deformation of the polymer matrix. Scratching of neat and wollastonite-containing EP copolymers involved periodic parabolic scratch tracks containing voids, which transformed to distinct zig-zag scratch tracks on reinforcement with micrometric wollastonite particles. The enhanced plastic flow in neat EP is facilitated by high ductility of the material and ability to nucleate voids, while in EP-W the plastic flow is suppressed because of reinforcement effect of wollastonite. On the other hand, zig-zag periodic scratch tracks were observed in both neat PP and PP-W, but the scratch tracks were not clearly discernible on reinforcement of PP with wollastonite. The resistance to scratch deformation is discussed in terms of tensile modulus, elastic recovery, scratch hardness, and reinforcement–matrix interaction.

Characterization by Fluorescence of the Distribution of Maleic Anhydride Grafted onto Ethylene−Propylene Copolymers

An ethylene−propylene random copolymer (EP) was maleated according to two different procedures which were expected to yield different distributions of succinic anhydride (SAH) along the backbone. The two maleated EPs, referred to as EP-I and EP-II, were labeled with fluorescent dyes such as pyrene and/or naphthalene by reacting 1-pyrenemethylamine (or 1-naphthalenemethylamine) with the SAH moieties randomly attached along the EP copolymer. As a result, the distribution of dyes mimics that of the SAH moieties along the polymer backbone. The labeled EP copolymers thus obtained were studied by steady-state and time-resolved fluorescence techniques in solution. Hexane and tetrahydrofuran (THF) were chosen as solvents. Pyrene excimer formation and fluorescence resonance energy transfer measurements were performed to demonstrate that the SAH moieties are attached to EP-I in a less clustered manner than to EP-II. These conclusions were confirmed by analyzing the fluorescence decays of the pyrene-labeled EPs with...

Molecular and microdeformation characteristics of ethylene-propylene copolymers during tensile loading

The microstructural modification during uniaxial tensile deformation of ethylene-propylene diblock copolymers (EP copolymers) at varying displacement rates was studied using atomic force microscopy (AFM) and Raman spectroscopy. Characterisation by AFM of the undeformed surface of the two copolymers (designated EP-M and EP-TC) indicated differences in arrangement (regular or irregular) of fibrils depending on their melt flow conditions. Type EP-M is a long chain copolymer manufactured with restricted flow, whereas EP-TC is a short chain copolymer obtained by controlled rheology. The microfibrils in both copolymers exhibited small kinks/nodules of ethylene-propylene. At the molecular level, long chain EP-M copolymer exhibited greater non-uniformity in the alignment of chains of molecules in comparison with short chain EP-TC copolymer. Atomic force micrographs taken at different fields of view for long chain EP-M copolymer tensile deformed at a low displacement rate indicated excessive stretching and merging of fibrils/microfibrils in the direction of the tensile axis, whereas short chain EP-TC copolymer exhibited reduced stretching of fibrils and microfibrils. With a subsequent increase in displacement rate of the tensile test, long chain EP-M copolymer continued to stretch along the tensile direction, but with reduced ability for stretching and merging of fibrils/microfibrils. On the other hand, tensile deformation of short chain EP-TC copolymer at a high displacement rate was irregular, and the fibrils/microfibrils were not preferentially stretched in the direction of tensile stress. The irregular deformation behaviour was a consequence of reorganisation of the microstructure. At the molecular level, stretching of individual molecular units occurred in both cases with an increase in displacement rate. However, the differences between the two copolymers were insignificant. Raman spectroscopy indicated that the rate of shift of frequency of Raman band per percentage strain was only marginally greater for long chain EP-M copolymer in comparison with short chain EP-TC copolymer, confirming AFM observations and suggesting only small differences in molecular deformation between the two copolymers.

Ductile behaviour of ethylene-propylene block copolymers

Flow behaviour during the tensile loading of ethylene-propylene diblock copolymers (EP copolymers) has been investigated at various strain rates. The strain rate sensitivity index indicated that the short chain (EP-TC) copolymer is more sensitive to strain rate than is the long chain (EP-M) copolymer. Scanning electron microscopy of ethylene-propylene diblock copolymers deformed at various strain rates revealed two types of fracture morphology, fibrillation and ductile ploughing. The area fraction of fibrillation decreased with an increase in strain rate, with a consequent increase in ductile ploughing. The surface of tensile deformed specimens of both block copolymers was characterised by wedge formation that increased with strain and strain rate of the tensile test. The density of wedges was greater in the centre of the longitudinal direction of the tensile specimen and less away from the centre. The higher plastic flow associated with wedges led to fibrillation type failure in the centre of the fracture, surrounded by a less ductile mode of failure, referred to as ductile ploughing. Regarding the difference in ductile behaviour of the two copolymers, long chain EP-M diblock copolymer exhibited greater fibrillation compared with short chain EP-TC diblock copolymer at a constant strain rate.

Alternating Copolymerization of Ethylene and Propylene: Evidence for Selective Chain Transfer to Ethylene

C1-symmetric ansa-metallocenes Me2E(Ind)(Flu)ZrCl2 (E = Si (1) and C (2)), upon activation with methylaluminoxane (MAO), produce atactic alternating ethylene−propylene copolymers (up to 92% EP dyads) with low molecular weight (less than 20K). Quantitative 13C NMR analysis of copolymer chain ends produced with 2/MAO indicates that the chain initiation/termination process is highly selective to generate a vinylidene as the unsaturated end group (terminating end) and an ethyl group as the saturated end group (initiating end). The high selectivity for sec-butyl end groups reveals a highly selective chain-initiation process where ethylene insertion is followed by propylene insertion at the initiating end. Chain transfer from a propylene-terminated polymer chain to a coordinated ethylene monomer is proposed to explain this selectivity. The facile cross-monomer chain-transfer process explains the much lower molecular weights obtained for the EP copolymers relative to the ethylene or propylene homopolymers.

The effect of hydrophobe chemical structure and chain length on the solubilization of griseofulvin in aqueous micellar solutions of block copoly(oxyalkylene)s

The solubilization capacities of micellar solutions of a series of block copolymers composed of hydrophilic poly(oxyethylene) (E) and hydrophobic poly(oxypropylene) (P), poly(oxybutylene) (B) or poly(oxyphenylethylene) (S, from styrene oxide) have been compared using the poorly water-soluble drug griseofulvin as a model solubilizate. A 1H NMR technique for determining the extent of solubilization has been developed. Considering the optimum result in each case, the amount of griseofulvin solubilized (expressed as moles griseofulvin per mole of hydrophobic units) by ES block copolymers was approximately nine times more than by EP copolymers and three times more than by EB copolymers. The mobility of the S-blocks in the cores of the ES copolymer micelles, as determined by 1H NMR spectroscopy, was sufficient to allow solubilization at ambient temperature.

Characterization of the Structure and Crystalline Polymorphism Present in Aliphatic Polyketones by Raman Spectroscopy

Raman spectroscopy has been used for the first time for the characterization of perfectly 1:1 alternating α-olefin:carbon monoxide aliphatic polyketones produced by the polymerization of ethene with carbon monoxide (ECO polymers) and mixtures of ethene and propene with carbon monoxide (EPCO polymers). A procedure to determine the methyl branch content arising from propene incorporation in EPCO polymers was established. This is based on the good correlation found between the intensity of a Raman band assigned to −CH3 bending and the propene incorporation determined by 1H NMR spectroscopy. A measure of the relative degree of crystallinity was made from the CO stretching band, and this was correlated with the heat of fusion determined by differential scanning calorimetry. Band shapes in the range assigned to −CH2− bending were attributed to factor group splitting effects (correlation splitting) and were interpreted to infer the presence of the two crystal forms (α and β) which have previously been identified by X-ray diffraction for aliphatic polyketones.

Crystalline structure in aliphatic polyketones

The crystalline structure of a number of perfectly 1:1 alternating α-olefin:carbon monoxide aliphatic polyketones produced by the polymerisation of ethene with carbon monoxide (ECO polymers) and mixtures of ethene and propene with carbon monoxide (EPCO polymers) have been studied by wide angle X-ray scattering (WAXS), Raman spectroscopy and differential scanning calorimetry (DSC). It is further confirmed that both WAXS and Raman spectroscopy are suitable techniques for the characterisation of the two polymorphs (α and β) reported for these materials. DSC detected the presence of small endotherms around 100°C associated with the transition from the α to the β phase only in the ECO material. In accordance with previous work, it is found that the α/β ratio is the highest for the ECO polymer and decreases with increasing propene content in EPCO polymers. Above 2.9 mol% of propene incorporation, EPCO polymers show exclusively β phase. Heat of fusion (degree of crystallinity) and melting point decreased with increasing propene level, as expected. Accordingly, crystalline density (as determined by WAXS) and lattice interchain interaction (as determined by Raman) were also found to decrease by increasing the propene incorporation.

13C NMR Studies of Ethylene-Propylene Copolymers Prepared with Homogeneous Metallocene-Based Ziegler-Natta Catalysts

13 C NMR investigation of EP copolymers at high ethylene content, prepared with highly isospecific, highly syndiospecific, and aspecific catalysts, is presented. The high stereoregularity of the iso- and syndiotactic samples and the complete regioregularity of all three samples greatly simplify the spectra and make it possible to check some of the chemical shift predictions and to perform other sequence assignments. The assignment of new sequences is based on (i) correlation of chemical shifts of homoand copolymers performed with the same catalysts, (ii) comparison of spectral intensities for samples of different compositions, and (iii) comparison with chemical shift values predicted by calculations. The detailed information obtained on comonomer and tactic sequences opens the possibility of describing the chain growth mechanism for the various catalytic systems and of correlating chain structure and copolymer physical and mechanical properties

Silane-Grafted / Moisture-Curable Ethylene—Propylene Elastomers for the Cable Industry

Abstract The present study has shown the capability of VTMOS grafting and moisture crosslinking of EP Elastomers. These capabilities are very large and have been shown to be dependent on various parameters. In EP copolymers, the crosslinking potential appears to be a function of the ethylene content, molecular weight, and molecular weight distribution. In the case of diene containing terpolymers, the process is shown to be limited by the diene content of the polymer through probable parasitic condensation reactions of grafted alkoxy silane. The good performance of the EP elastomers in silane-grafting/moisture-crosslinking can be also utilized in the modification of LDPE when crosslink rate improvement (elimination of hot-water treatment/hot-water treatment time reduction) or higher flexibility and lower shrinkage are needed. The positive results of this study made possible the development of EP elastomer compounds using silane-grafting and moisture-crosslinking for electrical applications. In Table IX and Table X are reported two EP elastomer compounds respectively for low-voltage and medium-voltage cable insulation applications. The key features of the above mentioned two EP elastomer compounds are the following: • high flexibility (comparable to conventional peroxide cure compound) • good mechanical properties • very fast extrusion (for productivity) • easy/versatile processing • high crosslinking state (set properties) • crosslinkable in ambient conditions.

Use of the lower critical solution temperature for the characterization of polymer mixtures and the study of their compatibility: Application to polyethylenes, polypropylene, and their copolymers

AbstractThe Lower Critical Solution Temperature (LCST) of polyethylene (PE), polypropylene (PP), and ethylene‐propylene block and random copolymers have been measured in heptanes. A thermogram related to the variation of the turbidity of the solution is obtained between 100 and 210°C. The temperature of the onset of the turbidity peak is defined as the LCST of the system. The width and the area of the turbidity peaks are tentatively associated with the polymer polydispersity and the amount of polymer involved in the phase separation. The thermograms of solutions containing both homopolymers show two distinct turbidity peaks situated at a 70°C interval. Correlations of molecular orientations in the concentrated phase, possible in PE systems but not in PP solutions, are at the origin of the lower LCST values for PE solutions. The LCST of copolymers are situated between those of the homopolymers but the dependence of the LCST on the copolymer ethylene content is different for block and random copolymers. Examples of thermograms are also given for mixtures of copolymers with PE and PP. By analysis of their thermograms, some commercial block EP copolymers were also found to contain PK and PP. This method seems well suited for characterizing polymer mixtures.