Ethylene Α-olefin Copolymers Research Articles

Polymer surface modification by photografting of functional nitroxides

The UV-initiated photografting of X-TEMPO onto the surface of ethylene/α-olefin copolymer (EOC) and of styrene-b-(ethylene-co-butene)-b-styrene (SEBS) block copolymer films is here described. In particular, 4-benzoyloxy-2,2,6,6-tetramethylpiperidine-1-oxyl (BzO-TEMPO), 4-(1-naphthoate)-2,2,6,6-tetramethylpiperidine-1-oxyl (NfO-TEMPO) and 4-(4,4,5,5,6,6,7,7,8,8,9,9,9-tridecafluorononanoate)-2,2,6,6-tetramethylpiperidine-1-oxyl (Fluo-TEMPO) were used as X-TEMPO derivatives to change the surface properties of the two polymer films. Infrared analysis (ATR-FTIR), electron paramagnetic resonance (EPR) and thermogravimetric analysis (TGA) confirmed the covalent immobilization of X-TEMPO onto the polymer surface. The fluorescence emission spectroscopy was used to investigate the optical properties of the NfO-TEMPO functionalized samples, while the contact angle measurements highlighted the wettability features of the surface modified with Fluo-TEMPO. A comparison of the data evidences that the properties of the free X-TEMPO derivatives have been completely transferred to the polymer giving “functional” films by a simple modification technique. Furthermore a discussion about the photografting mechanism as well as of the thermal robustness of the covalent bond between the X-TEMPO and the polymer is proposed.

Interfacial self-adhesion of polyethylene blends: the role of long chain branching and extensional rheology

The interfacial self-adhesion strength of polyethylene (PE) binary blends in temperatures higher than the melting point was investigated in relation to their components’ structures and elongational rheological properties. Four binary blends were prepared from the combination of a conventional polyethylene; LDPE or Ziegler-Natta LLDPE, with a metallocene catalyzed ethylene α-olefin copolymer; linear (Linear-m) or long chain branched (LCB-m). Interfacial adhesion was carried out by bringing two films into intimate contact under slight pressure and heat for 0.5 s. Adhesion strength was then measured by peeling immediately after sealing while the adherents were still in the molten state. Blending metallocene in 20, 40, and 60 wt% compositions with conventional PEs enhanced the self-adhesion. However, the adhesion strength of the blends containing 60 wt% metallocene resins was significantly lower than the adhesion strength of neat metallocene resins. This was interpreted to be due to the formation of a segregated layer of highly branched short chains of LDPE or Zn-LLDPE at the surface of films. The increase in adhesion strength of LDPE/Linear-m and Zn-LLDPE/Linear-m blends was more than LDPE/LCB-m and Zn-LLDPE/LCB-m blends. This was attributed to the faster reptation of linear chains, hence superior diffusion across the interface compared to LCB containing resin. The higher increase of adhesion strength for all compositions of LDPE blends was observed compared to their Zn-LLDPE counterparts. The temperature range in which the film showed a plateau of its highest adhesion strength was determined for all blend compositions. The results indicated that the temperature window of plateau adhesion strength for LDPE blends were broader than their Zn-LLDPE counterparts. Therefore, this work suggests that the final plateau temperature (T pf ) can be correlated with the area under stress–strain curve of the extensional rheological measurements, which is called toughness. Then, the higher melt toughness can result in a broader adhesion strength plateau.

Effects of process method and quiescent coarsening on dispersed-phase size distribution in polymer blends: comparison of solid-state shear pulverization with intensive batch melt mixing

We compare how solid-state shear pulverization (SSSP), batch melt mixing (BMM), and static melt-state annealing affect the morphology of an immiscible blend of polypropylene (PP) and ethylene-α-olefin copolymer (EOC). For 85/15 wt% PP/EOC blends, SSSP and BMM led to log-normal distributions of dispersed-phase particle size. The SSSP blend had smaller average particle diameters (e.g., D n = 0.24 μm) and a narrower particle size distribution (e.g., D w/D n = 1.17; D v/D n = 1.56) than the BMM blend (D n = 0.28 μm; D w/D n = 1.25; D v/D n = 1.79). The fact that BMM is subject to thermodynamically and flow-induced coalescence while SSSP is not, can lead to smaller particle sizes and a narrower distribution by SSSP. Although annealing at 200 °C for 30 and 90 min led to continuous growth of average particle size in the BMM blend, the particle-size dispersity remained virtually unchanged. In contrast, after 30-min annealing at 200 °C, the SSSP blend showed less growth in $$D_{{_{n} }}^{{^{3} }}$$ than the BMM blend but a dramatic increase in particle-size dispersity and a loss of the log-normal size distribution. Between 30 and 90 min, there was at most slight growth in $$D_{{_{n} }}^{{^{3} }}$$ , consistent with partial compatibilization caused by in situ block copolymer formation during SSSP, and major reductions in D w/D n and D v/D n close to those of the BMM blend and recovery of the log-normal size distribution. These results suggest that caution should be used in correlating immiscible blend properties to a particular average particle size as that value may not reflect possible complexity of the underlying size distribution.

Influence of compatibilizer on mechanical, morphological and rheological properties of PP/ABS blends

The objective of this work was to study the compatibilizer effect on polypropylene (PP) and acrylonitrile butadiene styrene (ABS) blends. The blends were coextruded and injection molded in various ratios of ABS with and without compatibilizers. Universal testing machine was employed to analyze the tensile properties of basic PP/ABS binary blends. From the mechanical testing, the impact and tensile properties of PP/ABS blend were optimized at 80/20 weight ratio. Various compatibilizers such as PP-g-MAH, SEBS-g-MAH and ethylene α-olefin copolymer were used and their comparative performance on binary blend was enumerated. Hybrid compatibilization effect was also studied and reported. However, the addition of compatibilizers showed the maximum increase in impact strength attributed to rubber toughening effect of ABS. The effect of compatibilizers on morphological properties was examined using scanning electron microscopy (SEM). SEM micrographs depicted the more efficient dispersion of ABS particles in PP matrix with the addition of compatibilizers. Further, interparticle distance analysis was carried out to evaluate the rubber toughening effect. The ABS droplet size in compatibilized PP/ABS blend was brought to minimum of 3.2 μm from 9.9 μm with the addition of compatibilizers. The melt rheology of PP/ABS blend systems was investigated through parallel plate arrangement in frequency sweep. Linear viscoelastic properties like storage (G′) and loss (G″) modulus and complex viscosity (η*) have been reported with reference to the virgin materials. It is understood that the combination of compatibilizers (hybrid compatibilizer) had a considerable effect on the overall blend properties.

Tuning structural parameters of polyethylene brushes on silicananoparticles in surface-initiated ethylene “living” polymerization and effects on silica dispersion in a polyolefin matrix

Surface-initiated ethylene “living” polymerization with covalently tethered Pd–diimine catalysts represents a novel technique for covalent surface functionalization of silica nanoparticles with polyethylene (PE) brushes. In this paper, we report on the successful tuning of various structural parameters of PE brushes in this surface-initiated polymerization technique, including brush length, density, and topology. To control/reduce the brush density, the density of the surface-tethered acryloyl groups for catalyst immobilization is adjusted by using mixed silane agents comprised of effective 3-acryloxypropyltrichlorosilane and inert ethyltrichlorosilane at different compositions in the surface functionalization step, which in turn adjusts the density of immobilized catalysts for rendering PE brushes. This approach gives rise to low-polydispersity PE brushes of controllable densities at the polymerization condition of 27 atm/5 °C: 0.022–0.055 chains per nm2 on a precipitated silica (Silica-I) and 0.07–0.17 chains per nm2 on a fumed silica (Silica-II). The length of PE brushes is controlled by adjusting the polymerization time, with the highest brush length of about 45 kg mol−1 achieved at 6 h of polymerization at 27 atm/5 °C. Unlike the linear brushes with short branch structures obtained at 27 atm/5 °C, hyperbranched PE brushes with compact topology are obtained at 1 atm/25 °C, benefiting from the chain walking mechanism of the Pd–diimine catalyst. The PE-grafted silicas of varying brush density and length are subsequently used as nanofillers to construct polymer nanocomposites with an ethylene–α-olefin copolymer as the matrix polymer. The effects of brush length and density on the nanofiller dispersion and physical properties of the composites are examined. This represents the first study on polyolefin composites containing silica nanoparticles grafted with polyolefin brushes as nanofillers.

Analysis of the molecular structure of ethylene hexene-1 copolymers produced over highly active supported Ziegler-Natta catalysts

The mechanical and rheological properties of ethylene α-olefin copolymers are governed by a molecular and supramolecular structure that depends on its molecular weight characteristics, comonomer concentration, and the uniformity of branching distributions for polymer chains with different molecular weights (compositional heterogeneity). Using state-of-the-art methods, we study the parameters of molecular weight distribution, molecular structure, and compositional heterogeneity of ethylene hexene-1 copolymers with different compositions, produced over highly active supported Ti-Mg and V-Mg Ziegler-Natta catalysts, and show the possibility of controlling these parameters to improve the quality of the resulting polymers.

Evolution of rheological properties and morphology development during crosslinking of polyolefin elastomers and their TPV blends with polypropylene

AbstractThis work investigates the evolution of the rheological properties of elastomeric dynamically vulcanized ethylene‐α‐olefin copolymers (ECs) and their blends with polypropylene (PP), during peroxide initiated crosslinking. Rheological techniques are used in conjunction with gel content measurements to determine the onset of gelation during static crosslinking. The complex viscosity and moduli follow power‐law dependence with respect to frequency at the gel point. The relaxation exponent and corresponding values of tan δ at the gel point are determined from the complex viscosity versus frequency curves and used as criteria for the determination of the instance of gelation. The evolution of morphology of thermoplastic vulcanizate (TPV) blends consisting of EC and PP during dynamic crosslinking is discussed in the context of the evolving rheological properties of the matrix and the dispersed phase that take place upon peroxide modification. TPVs having the crosslinked EC as the matrix present a very fine morphology, whereas the blends containing crosslinked EC particles, present a coarser morphology. POLYM. ENG. SCI., 2009. © 2008 Society of Plastics Engineers

Phase Structure and Crystallization Behavior of Polypropylene in-Reactor Alloys: Insights from Both Inter- and Intramolecular Compositional Heterogeneity

Systematic investigation on the compositional heterogeneity, phase structure, the crystallization and subsequent melting behavior of two commercial in-reactor alloys EB−P and EP−P (ethylene-co-butylene polypropylene and ethylene-co-propylene polypropylene) from Basell were conducted. The composition of the alloys and the chain structure of each component were characterized by combinatorial using of preparative TREF and 13C NMR technique. The compositional heterogeneities of both samples were further studied by SSA technique, and possible thermal fractionation mechanisms were then inferred. Correlations between the mechanical properties and the molecular architectures and phase structures were discussed. The results show that the excellent balance between toughness and rigidity of sample EB−P primarily benefits from the crystalline polyethylene homopolymer (HPE) phase and the amorphous ethylene-α-olefin copolymer (EC) component, which is proved to be enriched at the interface between the dispersed polyprop...

Effect of composition and comonomer type on the rheology, morphology and properties of ethylene-α-olefin copolymer/polypropylene blends

The rheology, morphology, thermal and mechanical properties of blends containing low molecular weight polypropylene (PP) and metallocene-based ethylene-α-olefin copolymers (ECs) have been investigated. Evaluation of the thermo-rheological properties of the blends showed that they are immiscible, both in the solid and melt state, over the whole range of compositions. Rheological properties were correlated to blend morphology, by using the Palierne emulsion model. The resulting low values of interfacial tension confirmed excellent compatibility between the phases. Addition of ECs in PP resulted in significant ductility improvement. The transition from plastic to elastomeric properties coincided with phase inversion. The butene-based EC was found to be the most beneficial in terms of impact properties. Fine morphologies, with sub-micron sizes of the dispersed phase, were obtained upon post-extrusion shearing of the blends.

Effect of molecular weight and average comonomer content on the crystallization analysis fractionation (Crystaf) of ethylene α-olefin copolymers

The effect of molecular weight and average comonomer content on the crystallization analysis fractionation (Crystaf) of ethylene/1-hexene copolymers was investigated experimentally and modeled via stochastic simulations. Molecular weight and comonomer content are the main structural parameters that affect the crystallizability of polymer molecules from dilute solutions. Sets of samples with varying molecular weight and comonomer content were prepared to study each effect separately. Although both structural parameters significantly affect the shape of Crystaf profiles, comonomer content is the main determining factor for Crystaf peak location for most molecular weights of interest. The results of the stochastic simulations show good qualitative agreement with the experimental data, but also indicate some clear limitations that might be related to the kinetics of crystallization effects during Crystaf analysis.

Experimental analysis of the grafting products of diethyl maleate onto linear and branched polyethylenes

This paper is focused on establishing the grafting products of diethylmaleate onto ethylene–α-olefin copolymers of varying comonomer contents. Several commercial ethylene/α-olefin copolymers ranging in comonomer contents from 0.35 to 3.70mol% were used, as well as a hydrogenated polybutadiene (HPB) with a 1,2 unit content of 13.9mol%. The polymers were functionalized with DEM in solution. The experimental techniques employed to verify the grafting and to ascertain the exact positioning of the insertion with respect to the branching points were: Fourier transform infra red spectroscopy (FTIR), carbon 13 nuclear magnetic resonance (13C NMR) and Distortionless enhancement polarization transfer NMR (13C NMR-DEPT). Thermal fractionation was performed by Differential Scanning Calorimetry (DSC) employing the successive self-nucleation and annealing technique (SSA).The results obtained show that the DEM insertion onto polyethylene chains occurs in secondary carbons of the main chain regardless of the copolymer branch type and content. The reasons for this behavior may be related to a statistical factor being involved in the peroxide radical attack since there is an excess of secondary carbons as compared to tertiary ones per PE chain. Also, steric effects produced by the size of the DEM molecules are probably involved in the DEM insertion step. Our 13C NMR-DEPT results suggest that DEM not only avoids the tertiary carbons where the branches are located but also, in polyethylenes with less than 4mol% branch content, it prefers to insert in the secondary carbons that are at least 5 carbon atoms away from the branch point. In those cases where unsaturations are present in PE chain ends, FTIR shows that they can also be depleted by DEM grafting. However, in the HPB case where no unsaturations are present and the branching content is very high, the insertion still occurs only in the secondary carbons of the main chain. The thermal fractionation performed by SSA corroborated the aforementioned results since the fractions with the longest linear chains were always the first to be depleted by the grafting reactions.

Comparative studies of ethylene–α-olefin copolymers by thermal fractionations and temperature-dependent crystallinity measurements

In this work the crystallization behavior and thermal fractionation results of various ethylene–α-olefin copolymers (1-butene, 1-hexene, 1-octene, 1-tetradecene, 1-hexadecene, 1-octadecene, vinylcyclohexane as comonomer) were evaluated using differential scanning calorimetry (DSC). The step crystallization (SC) method was compared with the successive self-nucleation/annealing (SSA) method. SSA exhibited better separation than SC, especially in the low temperature regions, and provided results in a shorter time. The temperature-dependent crystallinities confirmed that for all more branched polymers a lot of material is present at ambient and can crystallize below that temperature. Significant differences in the temperature-dependent crystallinity curves existed between ZN- and metallocene-catalyzed copolymers at the same comonomer level (and comonomer type).

Rheological characterization of molten ethylene–α-olefin copolymers synthesized with Et[Ind] 2ZrCl 2/MAO catalyst

The linear viscoelastic behavior of copolymers of ethylene with 1-hexene, 1-octene, 1-decene and 1-octadecene prepared with Et[Ind] 2 ZrCl 2/MAO is analyzed. The copolymers with α-olefin concentration greater than approximately 14 mol% have the simple rheological behavior with temperature that may be associated to linear polyethylenes with short chain branches. On the other hand, the polymers having comonomer concentration lower than approximately 14 mol% are thermo-rheologically complex materials. The rheological behavior of these copolymers may not be explained solely by the presence of long chain branching. A dendritic-like molecular structure with branches-on-branches has to be considered to explain the complexity observed in the case of the ethylene copolymers with low comonomer concentration and ethylene homopolymer. The complex chain structure would be the result of the incorporation of branched macromonomers in the polymers produced by single-site catalysts. The level of branching and complexity of molecular structure increases as the comonomer concentration decreases. No dependence with the length of the α-olefin was found in any of the analyzed parameters.

Phase Separation and Crystallization Behavior in Extruded Polypropylene/Ethylene-Propylene Rubber Blends Containing Ethylene-α-Olefin Copolymers

Liquid-liquid (L-L) phase separation and its effects on crystallization in polypropylene (PP)/ethylene-propylene rubber (EPR)/ethylene-α-olefin copolymer (ECP) ternary blends obtained by melt extrusion were investigated by time-resolved light scattering (TR-LS) and optical microscopy. L-L phase separation via spinodal decomposition (SD) was confirmed by TR-LS data. After L-L phase-separation at 250°C for various durations, the blend sample was subjected to temperature-drop to 130°C for isothermal crystallization and the effects of L-L phase separation on crystallization were investigated. Memory of L-L phase separation via SD remained for crystallization. The crystallization rate decreased with increasing L-L phase-separated time at 250°C. Slow crystallization for the long L-L phase-separated time could be ascribed to decrease in chain mobility of PP by decrease in rubbery components in the PP-rich region. The ethylene-octene copolymer exhibited good affinity with PP, leading to a slow growth of a concentration fluctuation during annealing.

Determination of Short-Chain Branches in Poly(vinyl chloride) and Ethylene-Vinyl Chloride Copolymers by Pyrolysis-Hydrogenation-Gas Chromatography

Short-chain branches (SCB) of poly(vinyl chloride) (PVC) and ethylene-vinyl chloride copolymer (EVC) samples were determined by reduction of the samples with tri-n-butyltin hydride(Bu3SnH) followed by high-resolution pyrolysis-hydrogenation-gas chromatographic measurement in the presence of nickel (Ni) as a hydrogenation catalyst. The branch contents were estimated from the relative peak intensities of characteristic key isoalkanes on the C10 and C11 fragment region in the observed pyrograms by comparing the data of reference model ethylene–α-olefin copolymers with known contents of methyl (C1), ethyl(C2), and butyl (C4) branches, respectively. The results obtained by this method were in reasonably good agreement with those found by 13C NMR. The correlations between polymerization conditions and the SCB contents in the PVC and EVC samples were also discussed. Significant features of the proposed method such as extremely high sensitivity using less than 1 mg of the sample and rapidness to finish one run in about 1 h would meet the potential needs for the SCB characterization in various polymers containing chlorine, which were used in practical fields.

Characterization of microstructure and fracture behavior of polypropylene/elastomer blends containing small crystal in elastomeric phase

AbstractFracture behavior of polypropylene (PP)/ethylene–propylene–rubber (EPR) blends containing small crystal in elastomeric phase was investigated. Various ethylene‐α‐olefin co‐polymers (ECP) were used as crystal components and put into the elastomer phase of the blends. The crystallite size was controlled by changing the composition of the ECP. From thermal analysis and electron microscopic analysis, it was found that the ECP having a smaller crystal had better affinity to EPR and thus the crystal was finely dispersed in the elastomeric phase. The ECP with large crystallite size had poorer affinity to EPR and tended to segregate in the elastomeric phase. Scratch resistance and tensile elongation of blends were measured and it was found that the small crystal drastically improved the above properties while the large crystal deteriorated them. The dispersed small crystal was thought to act as a crosslinking point in the elastomeric phase. The reinforcement of the elastomeric phase by such quasi‐crosslinking structure was the possible reason for the improvement of the mechanical properties of the blends. © 1995 John Wiley & Sons, Inc.

Thermal and X‐ray investigations of ethylene–α‐olefin copolymers obtained with highly active supported Ti–Mg and V–Mg catalysts

AbstractCopolymers of ethylene with propylene, butene‐1 and hexene‐1 were prepared using a titanium–magnesium (TMC) or a vanadium–magnesium catalyst (VMC). The copolymers were examined for thermal stability by TGA, melting and crystallization behaviour by DSC and crystallinity by XRD. Fractionated samples of ethylene–hexene‐1 copolymers were also similarly characterized. Results indicate that VMC produces copolymers with a higher degree of crystallinity and greater compositional homogeneity than TMC.

Structural and property correlations of ethylen-?-olefin copolymers

Ethyleneα-olefin copolymers differ from other polyethylenes in that: With the help of a cross-fractionation method we interpreted the differences of the experimental data, according to the molecular mass fractionation and the branching received. The thermal history has a great influence on ethylene-α-olefin copolymers, evidenced in the crystallization time for the same branching type, but with extremely varied branching percentages.

Melt finishing operations in CdF chimie LLDPE process

AbstractThe CdF Chimie LLDPE process uses retrofitted high pressure autoclave LDPE units to make a broad range of ethylene–α‐olefin copolymers covering melt indices from 0.5 to 50 and densities as low as 0.88. The melt pelletizing extruder may be used to improve polymer properties by mixing with selected additives, other polymers like LDPE, and miscellaneous reagents.

Effect of the composition and distribution of monomer units on properties of ternary ethylene-propylene-butylene copolymers

A study was made of the effect of composition and distribution of monomer units on the properties of ternary ethylene-propylene-butylene copolymers synthesized using the Ac 3V—di-isobutylaluminium chloride catalytic system. It was shown that the addition of but-1-ene to the composition of a two component copolymer reduces the glass temperature and improves the physical and mechanical properties of ternary copolymers. A study was made of the effect of distribution of ethylene units on the crystallinity of a ternary copolymer. It was shown that crystallinity of polyethylene type may appear on increasing the probability of forming long ethylene units containing a minimum of 10 members. A study was made by calculation and experimentally of the effect of composition and the probability of forming M i - M j structures during copolymerization on the glass temperature of ethylene α-olefin copolymers. Experimental and calculated results showed satisfactory agrement.