New-catalyst olefins are close to market.

The first conference ever devoted exclusively to metallocene-catalyst resin developments gave the clearest picture to date of how many of these unusual new polymers are close to market. Metcon'93 was held May 26-28 in Houston, sponsored by Catalyst Consultants Inc. of Spring House, Pa. Resin companies are committed to converting 1.4 billion lb of PE and 660 million lb of PP capacity to metallocene catalysts by 1995-96, said Catalyst Consultants' president Clyde Payn in his opening remarks. This includes 661 million lb/yr of metallocene-made PE in the U.S. by 1995 from Union Carbide Chemicals & Plastics Co., Danbury, Conn., and 220 million lb/yr of metallocene-made PP by 1996 from Exxon Chemical Co., Houston, Payn said.

Before the conference, only Exxon Chemical Co., Houston, and Dow Plastics, Midland, Mich., had announced commercial plans for metallocenebased resins in the U.S.

Metallocene-also called "singlesite" or "constrained-geometry"--catalysts, make resins with narrower molecular-weight distribution, more uniform comonomer incorporation and improved properties."reduction of low-molecular-weight tails reduces extractables, while fewer high-molecular-weight tails improve clarity. Strength and heatseal characteristics are all notably improved," said Payn.

Three major technical accomplishments were presented at the meeting. Mobil Chemical Co., Edison, N.J., reported what is believed to be the first successful gas-phase production of LLDPE in the U.S. with a catalyst. Fina Oil & Chemical Co., Dallas, described the first successful commercial-scale test run of syndiotactic PP in a bulk-phase, loop reactor. And the first thermoplastic resins made from cyclic olefin monomers are being commercialized in Japan and Germany using metallocene catalysts (see Technology Newsfocus).

GAS-PHASE RESINS

Mobil's continuous production of LLDPE using metallocene catalysts in a fluidized-bed, gas-phase reactor is believed to be the first in the U.S. Other early reports of successful processes used either high-pressure reactors (Exxon) or solution reactors (Dow). Mobil uses a proprietary metallocene catalyst of its own, said manager of catalyst R&D Dr. Allan Furtek. This catalyst made commodity LLDPE continuously for weeks on a 30-lb/hr pilot plant in Edison. A HMW resin of broad MWD was also made, "showing the versatility of the new technology," Mobil says.

The most important feature of the new material, which Mobil calls "Ultra Strength," is its very high dart impact properties (see table). A sample withstood up to 800 g (the limit of Mobil's test equipment) without breaking. Furtek believes the materials' real impact limit is much higher. Compared with standard hexene-based LLDPE, reactor granules of

Mobil's Ultra

Strength resin, however, are much denser, lacking the macropores typical of commercial LLDPE (see photos). Hexene content is lower in the Ultra Strength resin than in either commercial LLDPE or Mobil's Super-Strength hexene copolymer (see PT, May '92, p. 39) because of more uniform comonomer distribution.

Mobil made test runs with Ultra Strength resin on blown film lines and says it has very good bubble stability at 250 lb/hr," in spite of its narrow MWD. It shows higher melt viscosity and about 10% higher extruder pressures than conventional LLDPE. It also shows "very low haze," a 10[degrees] F drop in heat-seal initiation temperature, and low extractables, Mobil says.

FULL-SCALE RUN OF SYNDIO-PP

Fina's polymer R&D manager Dr. Edwar Shamshoum reported on the first full-scale production run of syndiotactic PP in a commercial liquid-pool bulk-phase reactor at Fina's La Porte, Texas, plant (see PT, March '92, p. 29). The run, starting April 28, "lasted more than a day and produced over 50,000 lb of sPP," Shamshoum says. "It lets us sample customers on a much larger-scale than was possible before, in order to explore potential applications."

Standard isotactic PP has methyl groups hanging on one side of the polymer chain, often compared to teeth on a comb. Syndiotactic has methyl groups on alternating sides of the chain. Shamshoum has previously reported that SPP can offer unusual toughness, clarity and gloss, plus a combination of softness and heat resistance.

Hoechst AG of Germany described new developments in isotactic PP homopolymers made by combining two or more different metallocene catalysts to create bimodal MWDs.

This approach can make a range of isotactic homopolymers by varying their crystallinity to yield resins with lower or higher levels of isotacticity (from 40 to 200 carbon links in length). A low-isotactic homopolymer, with shorter isotactic sequences, has lower melt temperature, greater toughness and transparency than materials with greater isotacticity longer isotactic sequences). For instance, Hoechst described a low-isotactic, metallocene-made PP with a 282 F melt temperature, notched Izod impact of 61 ft-lb/in., and 35% haze. The company has also made a highly isotactic homopolymer with 320 F melt temperature, notched Izod of 48 ft-lb/in.,