Metallocene Catalyst Technology Research Articles

Chemiluminescence studies on comparison of antioxidant effectiveness on multiextruded polyethylenes

Several polyethylene resins; high density polyethylene (Ph-HDPE, Phillips metal oxide catalyst) and linear low density polyethytlenes (LLDPE, formed using Ziegler–Natta catalyst and metallocene catalyst technology, m-LLDPE) were used in order to acquire an insight in to the effect of different polymerization catalyst systems on the melt stabilization performance of single AO. Chemiluminescence (CL) and melt flow rate (MFR) were used to analyze the degradation as a function of the number of passes through a twin-screw extruder. A good correlation was obtained, and the additives resulting with the best melt flow stability in the polymer were the same as those that promote the best CL results.

New Catalysts for Next Generations of Plastics

Plastics, which are basically polymer materials, are now an integral part of our daily lives: packaging, transport, textile, Hi-technology… Total Petrochemicals produces and develops useful lightweight and durable plastics that play a key role in the sustainable development of our world, making our lives easier, cleaner, safer and more enjoyable. These products include polyethylene, polypropylene, polystyrene but also since recently polylactic acid, a biopolymer based on a renewable raw material. Plastics are produced by polymerizing monomer units (ethylene in the case of polyethylene) under certain temperature and pressure conditions and most of the time in the presence of a catalyst. Catalysts, and more particularly organometallic species, are the cornerstones of the production of these polymers. Since 1980, the polyolefin field has undergone a revolution with the development of single-site catalysts referred to as metallocenes. The metallocene catalyst technology helps produce polyolefins, which boast improved chemical and physical properties and are less heavy and less bulky than those traditionally produced. Total Research Center-Qatar (TRC-Q) researchers, jointly with Total Petrochemicals Research and Development teams, prospect and develop new catalysts to design and manufacture innovative high-level performance plastics. The objective is to optimize the catalysts synthesis for industrial scale application and to produce such catalysts in high yields in the most efficient way. There is a direct relation between the catalyst structure and the polymer chemical and physical properties. The relation is investigated by changing the size and type of the catalyst substituents; metallic centers … (steric, electronic and symmetrical modifications of the catalysts); and studying the impact of such changes on the polymer microstructure. A set of products has been selected to explain this relation and bring to light new advances in polyolefins and biopolymers catalysis.

Conformation transition and crystalline phase variation of long chain branched isotactic polypropylenes (LCB-iPP)

The changes of conformation and crystalline structure of long chain branched isotactic polypropylene (LCB-iPP) under different crystallization temperatures and the effects of their special molecular architecture on the crystallization behavior were investigated by a combination of Fourier transform infrared spectroscopy (FT-IR), wide-angle X-ray diffraction (WAXD) and differential scanning calorimetry (DSC). In these polymers, long chain branching was introduced via in situ polymerization of polypropylene and an asymmetric diene monomer using the metallocene catalyst technology. Through the characterization of the specific IR band variation, it was proved that the conformational orders of helical sequences of LCB-iPP show great changes in different crystallization temperature ranges. In lower crystallization temperature range (100–130 °C), the intensities of all regular helical conformation bands of LCB-iPP increase with the increasing crystallization temperature and the regular helical conformation bands with more monomer units increase faster than that with less monomer units. In higher crystallization temperature range (130–150 °C), the intensities of all regular helical conformation bands of LCB-iPP decrease with the increasing crystallization temperature and the regular helical conformation bands with more monomer units decrease faster than that with less monomer units. The results of WAXD and DSC showed that LCB-iPP crystallizes from the melt as a mixture of α and γ forms. The content of the γ form increases with the increasing crystallization temperature, reaches a maximum value at 130 °C, and then decreases with a further increase of the temperature. At the same time, the crystallization of γ form is favored by the presence of the LCB structure of iPP. Moreover, the transitional temperatures of different helical conformations and crystallization structures of LCB-iPP show obvious correlations.

Shear-Induced Crystallization in Novel Long Chain Branched Polypropylenes by in Situ Rheo-SAXS and -WAXD

The characteristic properties of a new class of long chain branched isotactic polypropylene (LCB-iPP) polymers and the effects of its molecular architecture on the nature of orientation-induced crystallization precursor structures and crystallization kinetics in flow were investigated. In these polymers, long chain branching (LCB) was introduced via in situ polymerization of propylene and a diene monomer using the metallocene catalyst technology. The LCB-iPP polymers exhibited improved melt strength and mechanical properties, such as flexural modulus and tensile yield strength. As determined by gel permeation chromatography coupled with multiangle laser light-scattering (GPC−MALLS) analysis, it was noted that the LCB-iPP polymers had a significant population of highly branched chains in the high molecular weight component of the molecular weight distribution. Dynamic viscoelastic properties obtained by small-amplitude oscillatory shear technique showed that the increase in the degree of LCB caused a broadening of the melt relaxation spectrum, especially in the longest relaxation time regime. The effects of the unique molecular architecture of the LCB-iPP polymers on shear-induced crystallization development was investigated by in situ rheo-SAXS (small-angle X-ray scattering) and -WAXD (wide-angle X-ray diffraction) techniques. The results showed that upon application of a step shear (rate = 60 s-1, ts = 0.25 s, T = 140 °C), the oriented crystals fraction was substantially higher in the LCB-iPP polymers than that in the linear iPP polymer. The shear-induced crystallization rate of the LCB-iPP polymers was analyzed by an Avrami model; the value of Avrami exponent, n, ranged from 1.8 to 2.8 indicating a rod or disklike crystal growth geometry. In addition, the crystallization kinetics was enhanced by more than an order of magnitude when compared to linear iPP polymer under shear. The details of the crystalline phases determined from the WAXD data showed that, in addition to monoclinic α-form crystals, they were triclinic γ-form crystals. The contribution of γ-form crystals to the total crystalline phase was independent of the LCB level and was attributed to the regio defects of the chain. Enhancements in various mechanical properties as well as their strong crystal orientation and improved crystallization kinetics in flow, are due to the unique molecular architecture of these LCB-iPP polymers, which in turn are strongly coupled to their broadened and complex relaxation behavior.

Metallocene catalysts technology and environment

The polyolefin industry is increasingly confronted with the challenge to meet restricting environmental regulations. In parallel, the environmentally conscious public opinion (customer!), now globally organized, demands even more stringent anticipative actions to prevent any short or long term damages inflicted upon environment. The gradual shift from high pressure high temperature radical polymerisation for production of polyethylene to silica supported CrO3 based Phillips catalysts and several generations of stepwise improved TiCl3 based Ziegler–Natta catalyst technology has led to highly efficient catalytic systems accomplishing substantial improvement with respect to environmental issues. The development and progress of the last decade in single-site metallocene catalyst technology finally indicate that the advancing polyolefin industry has moved, in anticipation, towards even more modern technologies meeting the ultimate goal of employing clean processes that provide environmentally green products. Version française abrégée – Technologie et environnement des catalyseurs métallocènes. L'industrie des polyoléfines est confrontée au défi croissant des réglementations environnementales. En parallèle, la préoccupation pour l'environnement manifestée au niveau mondial par l'opinion publique (les clients !) exige les actions les plus anticipatives et les plus rigoureuses afin d’éviter les dommages infligés à court et à long terme à l'environnement. Le passage progressif des procédés de polymérisation à haute pression destinés à la production de polyéthylène par catalyseur Philips de type CrO3 supporté sur silice et les générations successivement améliorées de technologies de catalyseurs Ziegler–Natta (TiCl3/4) ont permis la réduction substantielle des problèmes environnementaux. Le développement et les progrès réalisés au cours de la dernière décennie sur le plan des catalyseurs métallocènes à site « mono-actifs » sont un exemple d'avancée anticipée de l'industrie des polyoléfines vers des procédés non polluants, objectifs ultimes de la technologie.

Compatibilization of polyethylene/polyamide 6 blends with functionalized polyethylenes prepared with metallocene catalyst

Metallocene catalyst technology was utilized to prepare functionalized polyethylenes, which were used as compatibilizers in polyethylene/polyamide 6 (40/60) blends. Polymerization of ethylene with 10-undecen-1-ol, 10-undecenoic acid, or N-methyl-10-undecenylamine resulted in ethylene copolymers with a small amount (0.2–1.2 mol %) of functionalized side chains. The blends were prepared in a twin-screw midiextruder, and injection molded with a mini-injection molding machine. The effect of the new compatibilizers on morphology and mechanical and thermal properties was studied. Toughness as well as stiffness and strength increased significantly with an addition of 10 wt % compatibilizer. Morphology became much more uniform, and crystallization and melting behavior changed. The Molau test with FTIR analysis was used to determine that the desired reactions between the compatibilizer and polyamide had actually taken place. The results showed functionalized polyethylenes prepared with metallocene catalysts to act as effective compatibilizers in polyethylene/polyamide 6 blends. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3099–3108, 1999

Rheological and molecular characterization of linear backbone flexible polymers with the Cole-Cole model relaxation spectrum

The empirical Cole-Cole distribution is an analytical three parameter model of the relaxation spectra that provides accurate fits to experimental dynamic viscosity data for many systems of commercial linear backbone flexible polymers. We demonstrate that for disparate systems of polyethylenes, the three Cole-Cole model parameters have simple power law relationships to moments of the molecular weight distribution enabling direct molecular interpretation of the mechanical relaxation spectrum. A simple relationship between the Cole-Cole distribution and the Cross model for the non-linear flow curve can be deduced utilizing the empirical Cox-Merz rule. Accurately representing the linear viscoelastic material functions with empirical analytical relaxation spectra containing relatively few fitting parameters that can be readily interpreted is a major advance in polymer characterization. The three Cole-Cole parameters effectively replace single point material characterizations such as melt flow index. Development of higher resolution polymer characterization methods is imperative with the advent of metallocene catalyst technology, which enables the molecular weight and backbone architecture to be carefully controlled.

Mitsui's Competitive Resin Requires Bigger Investment

With a history of about 60 years, the polyolefin industry is mature. But recent developments in metallocene catalyst technology have breathed new excitement into the production of these most commonplace plastics (C&EN, July 6, 1998, page 11). Worldwide, the technology leaders in the manufacture of polyethylene using metallocene catalysts are Dow Chemical and a joint venture between Union Carbide and Exxon named Univation Technologies. In Asia, Mitsui Chemicals has developed other metallocene catalysts and production processes for linear lowdensity polyethylene (LLDPE) and has built a world-scale plant making use of them. Although Mitsui Chemicals, along with Exxon, has led efforts worldwide to develop metallocene catalyst technology, the Japanese company is off to a slower start in terms of market acceptance of its process. This is despite having filed more metallocene-catalyst-related patents, from 1981 to the present, than any other chemical company. The polyethylene produced through Mitsui's technology...

Dow sues two firms over patent infringement

Intellectual property battles continue in the alluring field of single-site catalysts for polyolefin production (C&EN, July 6, page 11). Dow has filed lawsuits against Exxon and Univation Technologies, the licensing joint venture between Exxon and Union Carbide, over infringement of two different patents that cover its single-site or metallocene catalyst technology. The cases were filed in federal district court in Wilmington, Del., on July 24. None of the companies involved will discuss the details of this ongoing litigation. In the Exxon case, Dow claims that U.S. sales of Exxon's Exact polyethylene polymers—which are made by Dex-Plastomers, Exxon's joint venture with DSM—infringe Dow's U.S. patent 5,783,638. The U.S. Patent & Trademark Office issued this patent to Dow on July 21, three days before the suit was filed. Dow's specific complaint is that the Exact products are included in its broad claim of a composition comprising an ethylene polymer and at least one other natural or ...

Oxidation behavior and stabilization of metallocene and other polyolefins

AbstractEXXPOL® metallocene catalyst technology featuring very high‐productivity catalyst systems is expected to provide ethylene polymer compositions that show excellent oxidative stability based on their minimal unsaturation content and low innocuous metal residue of a non‐acidic nature. Metallocene ethylene polymers such as mLLDPE should be comparable to the most stable, commercial polyethylenes such as linear low‐density polyethylenes (LLDPE) from the UNIPOL® gas phase PE process.As background, the oxidation behavior and stabilization case of “total residue” polyolefins based on Ziegler‐Natta or Cr catalysis systems are reviewed. The interacting effects of polymer structure (i.e., tertiary hydrogen and unsaturation) and catalyst residue are discussed in terms of competing degradation reactions ‐ e.g., chain breakage, chain enlargement (or cross‐linking) and chain branching. The metal (Ti, V and Al) and chlorine residues from Ziegler‐Natta catalyst systems and the Cr residue for Cr catalyst systems can play a role in adversely affecting polymer oxidative stability. The residue levels and their nature govern whether there is an appreciable effect on oxidative stability, and therefore the stabilization requirements.Discussed are thermo‐oxidative studies under melt processing conditions which compare selected EXXPOL®/UNIPOL® mLLDPEs with several state‐of‐the‐art Ti/Mg and Cr catalyzed LLDPE from the UNIPOL® gas phase PE process and a high‐pressure, low‐density polyethylene (HP‐LDPE). Standard melt flow and discoloration tests are combined with specialized experiments using dynamic oscillatory shear rheometry and size exclusion chromatographyviscometry to illustrate performance shifts due to polymer composition differences under melt processing conditions. The advantages of dynamic melt rheometry are illustrated in terms of sensitivity to subtle degradation changes in molecular structure. EXXPOL®/UNIPOL® mLLDPE having low unsaturation and metal residue which are non‐catalytic to auto‐oxidation show excellent intrinsic oxidative stability. The discoloration resistance of EXXPOL®/UNIPOL® mLLDPE is high, comparable with HP‐LDPE and the high‐activity Cr catalyzed LLDPE. Stabilization ease for EXXPOL®/UNIPOL® mLLDPE is equivalent to product counterparts (similar MI and density) made using high‐activity, state‐of‐the‐art Cr or Ti/Mg catalyst systems designed for use in the UNIPOL® gas phase PE process.

Properties of Ultra Low Density Polyethylenes

With the new metallocene catalyst technology, ethylene copoly mers of unprecedented lower densities are being introduced rapidly. Since these very low density polyolefins offer interesting mechanical properties, a systematic investigation into their thermal and mechanical properties was made. It was found, for example, that despite the low densities achieved, wide compositional variations existed between materials. A comparison was also made between the thermal mechanical properties with optical properties, with the conclusion that compositional homogeneities are required for good optical properties.