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Metallocene catalysts can be thought of as high-powered, chemical rifles that allow polymer manufacturers to aim at specific, small targets when theymake polyolefin resins. Those targets can be resins with a specific molecular weight distribution, density, melt-flow rate, tensile strength, flexural modulus, or a combination of factors.

Whatever the pa-rameter, metallocene catalysts allow producers to alter reactor temperatures, pressures and other variables to achieve their goal.

Traditional catalysts used to make polyolefins are more like shotguns. A producer may use them to aim for specific targets, but the results - no matter how closely reactor variables are controlled - also include polymers outside the bull's-eye, and some polymers and residues not even near the target.

Plastic resin manufacturers see metallocene catalysts as a tool they can use to make improved products tailored for specific applications.

Resin makers regularly tout the toughness, durability and improved elasticity of metallocene

resins, and say they hope to make inroads into applications in packaging, medical and other industries in which PVC and other polyolefins now are used.

While those applications areseen as large-volume, general uses of these resins, the initial applications for resins made with metallocene catalysts have been in niche areas, as impact modifiers and in specialty applications.

Further, metallocene catalystsare very expensive, and the resins made with them also have been costly. Those high costs have fed skepticism about the ability of metallocene resins to make significant impacts on the extremely competitive high-volume thermoplastics markets.

Until recently, the uses of metallocene catalysts were limited to making types of polyolefins -polypropylene and polyethylene.

Dow Chemical Co., however, now has developed a PE/polystyrene interpolymer that it plans to produce in test quantities early next year.

Dow of Midland, Mich., believes it soon will be able to use its metallocene catalyst technology to produce designer resins. Dow believes its research will allow it to make and alter resins to suit specific customers' needs through a process it calls molecular architecture control.

Gerald Lancaster, director of development for polyolefins and elastomers for Dow Plastics, presented a paper May 18 at MetCon '95 in Houston, on molecular architecture control. Dow is using its technology today to develop new polymer products faster and with more predictable performance characteristics than before, he said.

The idea behind molecular architecture control, according to Chris Pappas, Dow Plastics marketing director for polyolefins and elastomers, is the ability to reduce development time for a new polymer from 1,000 days to six.

First, however, Dow is racing Exxon Chemical Co. of Houston and several other companies to get its metallocene-based plastic resins into production and to market.

Dow's Freeport, Texas, plant isramping up 250 million pounds of capacity that employs metallocene catalysts to make resins for a variety of markets, and is installing an additional 125 million pounds of capacity in Tarragona, Spain. That capacity primarily is for Dow's Affinity and Engage resin lines.

By the end of this year, Ed Gambrel, vice president for Dow's Insite business platforms, said Dow intends to introduce another family of resins made with metallocene technology to compete in commodity markets.

Meanwhile, Exxon has announced it intends to combine - by the end of this year - its metallocene catalyst technology with its supercondensing mode technology for gas-phase reactors to install 1 billion pounds of polyolefin resin capacity.

Both Exxon and Dow have said they believe these large projects will help them lower the costs of resins made with this technology. Even so, their costs are expected to be at premiums of 10-12 percent over the costs of existing high alpha-olefin comonomer, linear low density PE resins. HAO comonomer LLDPE resins themselves cost 10-12 percent more than other LLDPE resins.

While Dow and Exxon are rushing to beat each other to the market with commodity grades of resins made with metallocene technology, their competitors, Quantum Chemical Co. of Cincinnati; Union Carbide Co. of Danbury, Conn.; Mobil Chemical Co. of Fairfax, Va.; Montell Polyolefins USA of Wilmington, Del.; and others, are not standing still.

Mobil has announced its own development and patent of metallocene catalyst technology that it has used to produce commercial quantities of clarity film resins for packaging applications. Tom Luzzi, new business development manager, said Mobil Polymer is deeply involved in a very orchestrated and deliberate market development program, and does not have a time frame in which it expects to put its clarity film resins on the market.

Luzzi said he expects Mobil's metallocene technology to produce a resin that will take business away from LDPE produced in traditional high-pressure reactors. Luzzi spoke in a telephone interview June 6 from his office in Edison, N.J.

Meanwhile, Quantum has taken a public position that it intends to wait until its customers demand metallocene catalyst technology in commodity markets before it will enter the fray. Then, Quantum expects to license a technology to produce resins for the market.

``When metallocene catalysis becomes a factor in core PE markets, Quantum certainly will be there,'' Michael J. Baldwin, technology vice president, said at a recent news conference.

Separately, Union Carbide has devised another technology - dubbed Unipol II - that has taken it in another direction. Alex Makai, associate director of the firm's Unipol systems department, said Union Carbide sees unique properties in the resins made with metallocene catalysts, and acknowledges that those resins will be a significant factor in PE and PP markets.

However, Makai said, Union Carbide questions whether those resins will find solid applications in the high-volume segments of the market.

Makai echoed Quantum's Baldwin, saying: ``At the point where [resins made with metallocene catalysts] reach the stage of value and economics to the market, we at Union Carbide will be involved in making them.''

Dow and Exxon already have commercial resins made with metallocene catalysts available.

Because those products primarily are niche-oriented, further skepticism has arisen in the industry as to whether the research leaders eventually will move into competition with the largest sales categories of resins - LLDPE and LDPE. Metallocene catalyst technology does not have uses in making high density PE resins at this time.

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