Polyethylene Waxes Research Articles

Synthesis of linear low-density polyethylene waxes through chain-walking benzocycloalkyl nickel-catalyzed ethylene polymerization

Polyethylene wax is a highly useful material, and its diverse topological structures may have a significant impact on its applications. In this study, we have devised and synthesized a series of unilateral benzocycloalkyl α-diimine nickel catalysts. These nickel catalysts exhibited very high activities (1.06 to 10.25 × 106 g mol-1·h-1) and yielded branched (37–97/1000 C) polyethylene waxes with low molecular weights (Mn = 0.49 to 2.01 kg mol-1) and variable molecular weight distributions (1.79–35.05) in ethylene polymerization. Polymerization conditions such as pressure and temperature and catalyst structure such as backbone and axial substituents have an important influence on the polymerization activity and the properties of the resulting polyethylene waxes. High-temperature NMR reveals that these branched polyethylenes primarily feature short-chain branches, such as the methyl group, and exhibit a topology resembling that of low-molecular-weight linear low-density polyethylene (LLDPE).

Modifying the Properties of Bitumen Binders with Polyethylene Waxes

Modifying the Properties of Bitumen Binders with Polyethylene Waxes

Nickel catalyzed synthesis of branched polyethylene waxes using a hybrid steric strategy

Previous work suggests that the mixing of different substituents may have an unexpected effect on transition metal-catalyzed polymerization of ethylene. In this study, we synthesized a series of pyridine-imine Ni(II) complexes bearing o-diarylmethyl and o-aryl substituents. The hybrid steric Ni(II) complexes exhibited moderate activities (0.80–8.5 × 105 g·mol−1·h−1) and yielded branched (54–79/1000 C) polyethylene waxes with appropriate molecular weights (1.8 to 6.8 kg/mol) in ethylene polymerization. Surprisingly, methoxy and bimethoxy nickel catalysts exhibited very low polymerization activity commonality as well as significant different molecular weight polyethylene variability. The complexation of methoxy with diethylaluminum chloride resulting in simultaneous suppression of chain growth and chain transfer may be responsible for the above phenomenon. In addition, high temperature carbon spectra show that these polyethylene waxes are predominantly methyl branched.

Synthesis of chain‐end functionalized highly branched polyethylene waxes using sterically open α‐diimine Ni(II) catalysts

AbstractOur previous research showed that bis(benzocyclopentyl) α‐diimine Pd(II) complexes can facilitate chain transfer and polar monomer insertion in ethylene (co)polymerization. In this study, we synthesized two bis(benzocyclopentyl) α‐diimine Ni(II) complexes with different backbones. The Ni(II) complexes exhibited high activities (0.63–7.23 × 106 g·mol−1 h−1) and produced low molecular weight (2.7–7.8 kg mol−1) polyethylene waxes with high branching densities (43–86/1000 C) in ethylene polymerization. The use of a catalyst with a butyl backbone resulted in polyethylene waxes with significantly higher molecular weights. The axial substituent restriction strategy employed in the nickel catalyst allows for a sterically open structure, reducing the molecular weight of the resulting polyethylene by over two orders of magnitude, compared to ethyl catalysts without axial restrictions. This enables the production of polyethylene wax grade products with improved properties. The branched polyethylene wax chain ends were found to be aryl‐functionalized according to NMR characterization analysis, while the double bonds were absent. Also, the choice of solvent affects the branching, molecular weight, and chain end composition of the polyethylene wax.

Melt flow characterization of highly loaded cooper filled poly(acrylonitrile-co-butadiene-co-styrene)

The knowledge of the rheological behavior of hybrid polymer melts is essential to develop fused deposition modeling (FDM) filaments to print metal and ceramic goods. In this contribution, we performed an in-depth analysis of the morphology and the rheological behavior in the linear elastic domain of poly(acrylonitrile-co-butadiene-co-styrene) (ABS) highly filled with copper microparticles functionalized by bioinspired polydopamine, containing polyethylene waxes (PEW) as lubricant agent. The composite systems have potential applicability in manufacturing FDM filaments for the 3D printing of metallic parts. Small amplitude oscillatory shear (SAOS) tests, scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) demonstrate complex relationships among polydopamine coating, filler content, morphology, and rheological properties of the ABS/PEW/Cu system. Furthermore, PEW affects the interface adhesion and shear transmission between the ABS copolymer and the copper filler coated with polydopamine. Also, the polydopamine influences the rheological parameters of the polymer composites, namely retardation and relaxation times, melt flow, and cohesive energy density (Ec).

Development and Evaluation of Vegetable Resin Bio-Binders as Technological Alternatives to Bitumen

Recently, the feasibility of using bio-materials to reduce or completely replace the use of bitumen in asphalt mixture has gained increasing attention. Amongst others, an interesting solution is represented by the use of wood co-products with mineral or vegetable oils. This research focuses on the development of bio-binders using vegetable resin (VR) in unmodified form and waste olive oil (WOO) as the main components; in order to optimize the rheological properties of the blends, crumb rubber from end-of-life tyres (CR), Styrene-Butadiene-Styrene (SBS) and polyethylene waxes (PEW) are used as additives. In particular, this investigation focuses on studying different oil/rosin ratios and polymer contents to provide a clear framework on this bio-binder solution; conventional bituminous binders are taken as a reference. The alternative binders are characterized in terms of conventional properties such as penetration depth and softening point, as well as rheological response. Finally, two of the bio-binders studied are selected with the aim of assessing the mechanical properties of the resulting sustainable asphalt mixture using the Marshall Stability test and the Indirect Tensile Strength test, comparing the results with the threshold values set by an Italian road agency. Thus, this research represents a preliminary analysis of the potential application of bio-binder mixtures within the specification limits imposed by road agencies. Although this research represents a first attempt, the results are promising and prove to be worthy of further investigations.

Waxes from Long-Chain Aliphatic Difunctional Monomers.

Petrochemical polyethylene waxes (Mn = 800-8000 g/mol for commercial Ziegler waxes) as additives, lubricants, and release agents are essential to numerous products and production processes. The biodegradability of this class of compounds when unintentionally released to the environment is molar mass dependent and subject to ongoing discussions, and alternatives to conventional polyethylene waxes are desirable. By employing bottom-up and top-down approaches, that is nonstoichiometric A2 + B2 polycondensation and chain scission, respectively, linear waxes with multiple in-chain ester groups as biodegradation break points could be obtained. Specifically, waxes with 12,12 (WLE-12,12, WLE = waxes linear ester) and 2,18 (WLE-2,18) carbon atom linear ester repeat unit motifs were accessible over a wide range of molar masses (Mn ≈ 600-10 000 g/mol). In addition to the molar mass, the type of end group functionality (i.e., methyl ester, hydroxy, or carboxylic acid end groups) significantly impacts the thermal properties of the waxes, with higher melting points observed for carboxylic acid end groups (e.g., Tm = 83 °C for carboxylic acid-terminated WLE-12,12 with Mn,NMR = 1900 g/mol, Tm = 92 °C for WLE-2,18 with Mn,NMR = 2200 g/mol). A HDPE-like orthorhombic crystalline structure and rheological properties comparable to a commercial polyethylene wax suggest WLE-12,12 and WLE-2,18 are viable biodegradable and biosourced alternatives to conventional, petrochemical polyethylene waxes.

Synthesis of branched polyethylene waxes using benzocycloalkyl pyridine-imine Ni(II) catalysts with dibenzosuberyl group

Our previous works revealed that dibenzosuberyl groups can suppress chain transfer reactions in many late-transition metal-catalyzed ethylene polymerization systems. In this study, we synthesized three benzocycloalkyl or naphthyl pyridine-imine Ni(II) complexes with a single o-aryl dibenzosuberyl substituent. The generated Ni(II) complexes exhibited moderate activities (3.6–7.6 × 105 g·mol−1·h–1) and yielded branched (44–69/1000 C) polyethylene waxes with appropriate molecular weights (3.0–9.1 kg/mol) in ethylene polymerization. Moreover, compared to the planar naphthyl Ni(II) complex, the more stereospecific benzocyclohexyl Ni(II) complex produced 2 times higher molecular weight polyethylene. Most importantly, the single o-aryl dibenzosuberyl substituent can significantly suppress chain transfer during polymerization and increase the molecular weight of the polyethylene produced in this pyridine-imine Ni(II) system with respect to the dibenzhydryl substituent. The resulting branched polyethylene waxes with suitable molecular weights can be used as additives in the plastic processing, coating and dyeing industries.

Co‐crystallization behaviors and thermo‐physical properties of SSPCM consisting of an extra low melt viscosity HDPE and paraffin waxes

AbstractShape stabilized phase change materials (SSPCMs) consisting of an extra low melt viscosity high‐density polyethylene (lv‐HDPE) and paraffin waxes (PW) were fabricated using a twin screw extruder. Thermal and mechanical properties of these composites were assessed. The latent heats (ΔH) of the SSPCMs fabricated were up to 78 J g−1. Co‐crystallization between lv‐HDPE and paraffin waxes increased with increasing wax content. Dynamic mechanical thermal analysis confirmed the paraffin wax having a higher melting point (H‐PW, Tm ranging from 56 to 58°C) plasticized the lv‐HDPE, decreasing both its crystalline content and melting temperature. Static mechanical testing, disregarding the form of deformation (tension, flexural, and compression), showed addition of paraffin waxes resulted in a diminution of all mechanical properties of lv‐HDPE, but the properties of the composites with H‐PW were good in comparison to those with a lower melting point wax (L‐PW, Tm ranging from 18 to 23°C). Evidences from Cole–Cole plots obtained from oscillatory rheology experiments showed there was no interaction between lv‐HDPE and H‐PW, inducing a heterogeneous blend in contrast to the more homogeneous lv‐HDPE/L‐PW composites.

Nanohybrid emulsions stabilized with calcium phosphate oligomers prepared by self‐emulsification technology for ultra‐high abrasion resistance coating

AbstractPolyethylene waxes are low molecular weight polyolefin synthetic waxes with outstanding mechanical properties, lubricating performance, and chemical stability, which are widely used in various industrial fields. The nonpolar nature of polyethylene waxes leads to low surface energy and poor compatibility with polar materials, which limits their development applications. Therefore, developing composites with better mechanical properties is essential to overcome this drawback. In this work, calcium phosphate oligomers (CPO) are employed to stabilize nano‐emulsions of polyethylene wax modified with maleic anhydride. The emulsification of emulsions was investigated under different NaOH dosages, temperatures, emulsification times, and rotational speeds. The prepared emulsions are used as additives in polyurethane coatings and starch slurries. The CPO can reduce the particle size of the nanohybrid emulsions and greatly improve the abrasion resistance of some polymer films as additive agents. The organic and inorganic units were homogeneously combined with properties of a complete and continuous organic–inorganic network. The emulsions exhibit ultra‐high abrasion resistance when applied to polyurethane coatings and starch pastes, broadening their range of applications.

Characterization of porous biomaterials of 316L stainless steel made from polyethylene waxes as pore-forming agents

For biomedical purposes, the 316L stainless steel has been used due to its high mechanical strength and its biotolerability by the human body. Its porosity allows the growth of living tissue within the implant, which improves fixation to hard tissues. Porous 316L stainless steel specimens were produced by powder metallurgy with controlled porosity by the addition of different polyethylene waxes granulometries (50 and 100 mm) and concentrations (0.0, 1.0, 2.0, 3.0 and 4.0%). The elastic modulus, porous morphologies and densities of the steel samples were determined. Thus, the densities and the elastic modulus were evaluated statistically through Tukey’s test. The results showed that the porosity increases proportionally to polyethylene wax concentration, but the elastic modulus decreases. The Tukey’s Test showed that there are no significant differences in most samples using the two waxes at most concentrations. Range values of 1.89 to 1.51 GPa using wax with 50 mm, and 1.72 to 1.19 GPa were respectively obtained using 100 mm particle size. The highest pore size (45 mm) and the lowest elastic modulus (1.19 GPa) were obtained by use of 4.0% of wax.

Polyethylene Waxes with Short Chain Branching via Steric and Electronic Tuning of an 8-(Arylimino)-5,6,7-trihydroquinoline-nickel Catalyst

Ten examples of nickel(II) halide complexes [8-{N(2,4-(C15H13)2-6-RC6H2N)}C9H8N]NiBr2 [R = Me (Ni1), Et (Ni2), iPr (Ni3), Cl (Ni4), or F (Ni5)] and [8-{N(2,4-(C15H13)2-6-RC6H2N)}C9H8N]NiCl2 [R = Me (Ni6), Et (Ni7), iPr (Ni8), Cl (Ni9), or F (Ni10)], each incorporating a sterically encumbered N,N-chelating 8-[2,4-bis(dibenzocycloheptyl)-6-R-phenylimino]-5,6,7-trihydroquinoline ligand, are disclosed. Full details for the preparation of these complexes as well as the zinc-mediated synthesis of precursor ligands L1–L5 are given. Structural characterization of Ni3(H2O), Ni6, Ni7(H2O), and Ni8(H2O) reveals halide-bridged dinuclear structures of the type (N,N)NiX(μ-X)2NiX(N,N) with the ortho-substituted dibenzocycloheptyl groups providing steric protection to each metal center. In the presence of ethylaluminum dichloride (EtAlCl2) or methylaluminoxane (MAO), Ni1–Ni10 displayed high activities for ethylene polymerization [≤6.17 × 106 g of PE (mol of Ni)−1 h–1 for Ni6/EtAlCl2 at 20 °C], generating low-molecular weight polyethylene waxes. Notably, catalysts incorporating a 6-alkyl group (Me, Et, or iPr) as the N-aryl substituent proved to be more active than their 6-halide (Cl or F) counterparts and formed relatively higher-molecular weight polymers (Mw range of 9.1–22.9 kg mol–1) with a narrow dispersity. Moreover, analysis of these waxes by 13C nuclear magnetic resonance spectroscopy showed that they typically possessed short chain branching (>83% methyl) with branching densities of 79–90 branches per 1000 Cs. In addition, chain end analysis revealed the presence of both vinyl (−CH═CH2) and internal vinylene (−CH═CH−) functional groups, highlighting the role of both β-H elimination and isomerization.

Catalytic oligomerization and polymerization of ethylene with complexes of iron triad metals: influence of metal nature and new prospects

In the last five years the field of catalytic oligomerization and polymerization of olefins using complexes of late transition metals has been the most intensively developing area of post-metallocene catalysis. This review is devoted to detailed analysis of the influence of metal nature on the catalytic properties of systems based on complexes of iron triad metals. Some novel and developing areas of application of such complexes in olefin oligomerization and polymerization (ethylene trimerization, production of olefins with an odd number of carbon atoms and polyethylene waxes, targeted synthesis of heavy fractions of ethylene oligomers) are surveyed. Different approaches to the heterogenization of catalysts on various solid supports are considered.The bibliography includes 225 references.

Fluorinated Sterically Bulky Mononuclear and Binuclear 2-Iminopyridylnickel Halides for Ethylene Polymerization: Effects of Ligand Frameworks and Remote Substituents.

In the present work, four new mono(imino)pyridine ligands, 2-((2,4-bis(bis(4-R-phenyl)methyl)-6-fluorophenylimino)methyl)pyridine (R = H, L1; R = OCH3, L2; R = F, L3) and 2-((2-(bis(4-fluorophenyl)methyl)-4-((3-(bis(4-fluorophenyl)methyl)-4-amine-5-fluoro-phenyl)(phenyl)methyl)-6-fluorophenylimino)methyl)pyridine (L4), have been designed in good yields. Additionally, three novel benzhydryl-bridged bis(imino)pyridine ligands, 2-(2-(bis(4-R-phenyl)methyl)-6-fluoro-phenylimino)pyridine (R = H, L5; R = OCH3, L6; R = F, L7), were also prepared for comparison. All these organic compounds have been characterized by FT-IR analysis, 1H/13C NMR spectroscopy, and elemental analysis. The treatment of L1–L7 with nickel halides afforded the corresponding monometallic (Ni1–Ni4) and bimetallic (Ni5–Ni7) nickel complexes in moderate to good overall yields. Upon activation with methylaluminoxane (MAO), Ni4Cl showed the highest activity up to 8.3 × 106 g of polyethylene (PE) (mol of Ni)−1 h–1 among Ni1–Ni7 for ethylene polymerization. In all cases, unsaturated PEs with low molecular weights (0.7–13.3 kg mol–1) were produced effectively. The introduction of remote para-substituents into the benzhydryl groups showed a beneficial effect on catalytic activity with the overall activities following the order of Ni–F > Ni–OCH3 > Ni–H. In addition, these para-substituents were also found to affect not only the catalytic performance of catalysts but also the branching content of the PE product. Generally, the resultant PE waxes were moderately branched and contained both terminal vinyls (−CH=CH2) and internal vinylenes (−CH=CH−) while with different ratios of vinyls to vinylenes. Notably, the polymers produced using para-methoxy-substituted Ni2/MAO and Ni6/MAO possessed the least branching content and uniquely high vinyl contributions.

Temperate UV-Accelerated Weathering Cycle Combined with HT-GPC Analysis and Drop Point Testing for Determining the Environmental Instability of Polyethylene Films

Polyethylene films are one of the most frequently used packaging materials in our society, due to their combination of strength and flexibility. An unintended consequence of this high use has been the ever-increasing accumulation of polyethylene films in the natural environment. Previous attempts to understand their deterioration have either focused on their durability using polymer analysis; or they have focused on changes occurring during outdoor exposure. Herein, this study combines those strategies into one, by studying the chemical and physical changes in the polyethylene structure in a laboratory using molecular weight and IR spectroscopic mapping analysis, combined with temperate UV-accelerated weathering cycles. This approach has been correlated to real-world outdoor exposure timeframes by parallel testing of the sample polyethylene films in Florida and France. The formation of polyethylene microparticles or polyethylene waxes is elucidated through comparison of drop point testing and molecular weight analysis.

Doubly fused N,N,N-iron ethylene polymerization catalysts appended with fluoride substituents; probing catalytic performance via a combined experimental and MLR study

In agreement with the MLR analysis, the fluorinated iron precatalyst, R1 = F, R2 = R3 = CH(p-FPh)2, proved the most active at 70 °C generating strictly linear polyethylene waxes.

Bis(imino)-6,7-dihydro-5H-quinoline-cobalt complexes as highly active catalysts for the formation of vinyl-terminated PE waxes; steps towards inhibiting deactivation pathways through targeted ligand design.

A set of five related bis(imino)-6,7-dihydro-5H-quinoline-cobalt(ii) complexes, [2-(ArN = CPh)-8-(NAr)-C9H8N]CoCl2 (Ar = 2,6-Me2C6H3Co1, 2,6-Et2C6H3Co2, 2,6-i-Pr2C6H3Co3, 2,4,6-Me3C6H2Co4, 2,6-Et2-4-MeC6H2Co5), have been synthesized in reasonable yield by the template reaction of cobalt(ii) chloride hexahydrate, 2-benzoyl-6,7-dihydro-5H-quinolin-8-one and the corresponding aniline. The molecular structures of Co1 and Co4 highlight both the differences in the two imino-carbon environments (phenyl-capped chain vs. cyclic) and also the steric properties exerted by the bulky Nimine-aryl groups. On pre-treatment with either modified methylaluminoxane (MMAO) or methylaluminoxane (MAO), all complexes proved productive catalysts for the polymerization of ethylene. In particular, Co1/MAO was the most active reaching a very high level of 1.62 × 107 g PE per mol (Co) per h over a 30 minute run time. Owing to the presence of the imino-phenyl substituent, Co1–Co5 were able to exhibit good thermal stability by displaying appreciable catalytic activity at temperatures between 50 and 80 °C, generating polyethylenes with narrow dispersities (Mw/Mn range: 1.66–3.28). In particular, the least sterically bulky precatalysts, Co1 and Co4 formed polyethylene waxes (Mw range: 1.94–5.69 kg per mol) with high levels of vinyl unsaturation as confirmed by high temperature 1H/13C NMR spectroscopy and by IR spectroscopy.

Fluorinated cobalt catalysts and their use in forming narrowly dispersed polyethylene waxes of high linearity and incorporating vinyl functionality

The depicted cobalt catalysts bearingortho-fluorine and fluorinatedortho-benzhydryl substituents displayed a preference for forming highly linear PE waxes; DFT studies have been used to probe this selectivity.

CHARACTERIZATION OF LUBRICANT POLYETHYLENE WAXES

Polymer processing is become easy while using lubricant in a proper way. Hence viscosity reduction and gelation behavior/release effect of lubricants help the production speed and quality. In this manner by the growing need for lubricant characterization two technical-grade polyethylene (PE) waxes were investigated. PE is one of the most used lubricant and study by characterizing them using Fourier Transform Infrared (FT-IR) spectrophotometry, Scanning Electron Microscopy (SEM), X-ray Diffraction (XRD), Differential Scanning Calorimetry (DSC) and Thermogravimetric analysis (TGA) to elucidate their structural, molecular and thermal characteristics in order to assess their effectiveness and suitability as lubricants in carpet manufacturing.

Post-functionalization of narrowly dispersed PE waxes generated using tuned N,N,N′-cobalt ethylene polymerization catalysts substituted with ortho-cycloalkyl groups

Six structurally related bis(arylimino)trihydroquinolyl-cobalt (II) chloride complexes [2-(ArNCCH3)-8-(ArN)-5,6,7-C9H8N]CoCl2 (Ar = 2-(C5H9)-6-MeC6H3Co1, 2-(C6H11)-6-MeC6H3Co2, 2-(C8H15)-6-MeC6H3Co3, 2-(C5H9)-4,6-Me2C6H2Co4, 2-(C6H11)-4,6-Me2C6H2Co5, 2-(C8H15)-4,6-Me2C6H2Co6), distinguishable by the ring size of the ortho-cycloalkyl substituent and type of para-R group, have been synthesized and characterized. A distorted square pyramidal geometry is a feature of the molecular structure of Co4 with the two ortho-cyclopentyl groups located on neighboring N-aryl groups trans-configured. Compounds Co1 – Co6, on activation with methylaluminoxane (MAO) or modified MAO (MMAO), proved highly productive catalysts for ethylene polymerization at 60 °C [up to 17.1 × 106 g (PE) mol−1(Co) h−1 for cyclopentyl-containing Co4/MAO]; even at 90 °C significant activity was attainable (up to 6.75 × 106 g (PE) mol−1(Co) h−1). Strictly linear polyethylene waxes of low molecular weight (ca. 1.50 kg mol−1), narrow dispersity (Mw/Mn range: 1.1–2.4) and incorporating high levels of vinyl end-groups were generated. Post-functionalization of these PE waxes by epoxidation, thiol-ene addition and cross-olefin metathesis to form e-PE, PE-S-CH2CH2NH2·HCl and PE-MMA, respectively, has been demonstrated. For comparative purposes, [2-(ArNCCH3)-8-ArN-5,6,7-C9H8N]CoCl2 (Ar = 2,4,6-Me3C6H2Coo-Me, 2-(Ph2CH)-4,6-Me2C6H2Coo-CHPh2) have also been prepared and evaluated as polymerization catalysts.