SCIENCE/TECHNOLOGY traditional additives based on bromine or antimony. For fire-retardant polycarbonate housings, Freitag says, it is now possible to compound the resin with a salt that cross-links it under fire conditions to inhibit flames and melting. Alloys of acrylonitrile-butadiene-styrene (ABS) and polycarbonate can now be made to be fire-retarding by using phosphorus compounds that quench free radicals of combustion. And mineral fillers render polyamides fire retardant. Chemical intuition has already guided researchers to an improved polycarbonate, Freitag says. Conventional polycarbonate is made from bisphenol A, which is a condensation product of phenol and acetone and has a glass transition temperature (T , a kind of melting point) of 150 °C. The new polycarbonate is made from what Freitag calls "bisphenol I," and has a Tg of 240 °C. This higher use temperature suggests applications in housings for the new superhot halogen-bulb desk and floor lamps. Bisphenol I is a condensation product of phenol and 3,3,5-trimethylcyclohexanone, a derivative of isophorone. The bulky methyl groups on the cyclohexane ring inhibit rotation of phenyl rings in the resin, Freitag explains, hampering polymer chain motion and thus delaying softening until the 240 °C temperature is reached. But then the conformational fluxion of the cyclohexane rings swings the methyl groups out of the way, freeing the polymer chain and resulting in an abrupt transition to a melt of low viscosity (therefore easily flowing and workable). Freitag says recycling may be either recovering energy content by incineration or reuse of the plastic itself. He cites 10-year-old ABS Volkswagen grills that can be ground up and the regrind added at a 30% loading to virgin resin, with that compound then being molded into new grills. Recycling is a benefit that will come from improvements in polypropylene in the 21st century, also claims Paolo Galli, research director at the Montecatini technical center in Ferrara, Italy. He says these improvements will lead to increasing use of solid polypropylene auto parts and upholstery fiber. Then all of the polypropylene content of scrapped cars can be recycled at once. The improvements that Galli sees coming will make polypropylene a chal-
ment of all the new processes and performance resins discussed at the symposium. This was the view of Alexander MacLachlan, who is senior vice president for research and development at Du Pont. Universities will continue to be principal sources of this knowledge, MacLachlan says. And although industry will continue to provide a small proportion of university research funding, new forms of partnership will emerge. As companies face technological problems in process and resin development, MacLachlan says, they must persuade academicians that there are underlying scientific problems worthy of scholarly research. Academic scientists sometimes find it hard to see the connection between technological problems and their underlying scientific opportunities. Du Pont will restrict research grants to professors who can see the connection. MacLachlan gives the example of a reMacLachlan: new partnerships emerging cent partnership between Du Pont and one professor's group. Du Pont had a lenger of polycarbonate, polystyrene, need for certain high-pressure data. The and polyurethane, and will result from professor had the equipment and his what he calls catalyst replication poly- group had the expertise to gather it. So merization. In this technique, each cata- Du Pont granted $80,000 per year over lyst particle serves as a nucleus for for- three or four years for the project. The mation of a thin skin of polypropylene project involved visits by Du Pont scienaround it. Galli calls this stage prepoly- tists to the university and by the profesmerized catalyst. From there, resin forms sor and his graduate and postdoctoral as a series of layers like skins on an on- students to Du Pont. The results of the ion. Or, in another approach, the result project were publishable. may not be an onion structure but a Stephen Stinson spongy mass. In any case, the mass of resin grows by replicating the shape of the catalyst particle. Control of the polymerization gives control over the molecular weight range and distribution to vary the properties of the resin. And the onion-skin structure solves An organic reaction developed by rethe problem of how to blend polymers. searchers at Monsanto could make it Most polymers are incompatible with possible to produce some industrially one another, resist mixing, and tend to important aromatic amines in an enviseparate into phases after mixing. This ronmentally safer way that eliminates incompatibility results from a lack of en- the need to use halogenated aromatics. tropy gain. Small molecules mix well The aromatic amines generated by the with solvents, both because of a favor- reaction are produced in large quantities able enthalpy of interaction and because for making antioxidant additives for mixing increases the entropy of the sys- tires and other rubber products. tem. Mixing of macromolecules gives The reaction was developed by negligible entropy gain. Galli says it is Michael K. Stern, Frederick D. Hileman, possible to add monomers other than and James K. Bashkin of the chemical propylene to the growing resin particles. sciences department of Monsanto corpoThis gives an onion structure in which rate research, St. Louis. It was recently each skin is a different resin type. Thus patented (U.S. patent No. 5,117,063), and its mechanism was reported in the Nov. the resin is born blended. In the 21st century, knowledge will 4 issue of the Journal of the American be the limiting resource to develop- Chemical Society [114,9237 (1992)].
Aromatic amine route is environmentally safer
CIRCLE 10 ON READER SERVICE CARD
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NOVEMBER 30,1992 C&EN
Thiotopics ELF ATOCHEM THIOCHEMICALS
NO- 3
Vultacs: Versatile Building Blocks As a series of rubber vulcanizing agents, Elf Atochem's Vultacs have been helping rubber product performance for over 40 years. They are well-known for their ability to enhance rubber aging properties and help in the covulcanization of blends. Elf Atochem provides a full line of grades to meet your specific needs. These alkyl phenol disulfides exhibit vulcanizing activity roughly proportional to the sulfur content. What makes these low molecular weight oligomers so unique, is their versatile, multifunctional structure.
Vultacs phenol groups can impart antioxidant and biocidal activity, or serve as sites for further reactions, such as ethoxylation and metal-chelate formation. The disulfide linkage can further enhance antioxidant and biocidal activities, serve as a sulfur-donor (as in vulcanization) or sulfur-scavenger (to form polysulfides), and provide a highly reactive site for oxidation, reduction or cleavage reactions. The Advantages Of Vultacs Vultacs can be used as either complete or partial replacements for sulfur thirams. When used as a partial replacement for sulfur, Vultacs tend to improve dispersion of other additives in the rubber. In SBR and nitrile compounds, replacing parts of sulfur with Vultac increases rate of cure, provides higher and more uniform tensile strength, gives better elongation and improves aging. For handlers, another advantage is Vultacs low toxicity. Its oral toxicity in rats is LD50 > 5000 mg/KG (toxicity tests on Vultac 7). This means you can handle Vultacs with confidence.
Perfect For A Variety Of Applications The combination of Vultacs chemical properties makes it an enticing candidate for a number of commercial applications. With the known activity of phenol groups to inhibit peroxide formation, and the known property of bivalent sulfur to destroy hydroperoxides, the Vultacs possess built-in synergism as antioxidants for hydrocarbons, plastics, functional fluids and lube oils. The biocidal activity of the phenol groups add to their potential as preservatives, anti-fungal agents, paint additives, wood-treating agents, corrosion inhibitors and much, much more. Vultacs are also intermediates to mercaptophenols (using a variety of chemical reducing agents), and, after blocking the phenol group, to sulfoxides, sulfones, thiosulfonates and phenolsulfonic acids (with
strong oxidizing agents). They can react with elemental sulfur to form the corresponding phenolic polysulfides, which can serve as sulfur-donors and anti-wear/antiweld agents for high performance lubricants. To learn more about Elf Atochem Vultacs, check and mail the reply card on back.
TPS—Extreme Pressure Lubricant Additives Many factors are taken into consideration when preparing lubricant and metal working formulations. When the sliding conditions between two surfaces are "mild" in terms of pressure and temperature, common anti-wear additives provide effective performance. These boundary lubricants decompose as pressures and temperatures become more severe, reducing their effectiveness. The properties of a formulation can be improved with the addition of extreme pressure (EP) additives. Typical EP additives are oil soluble chlorine, sulfur and phosphorous compounds that react under high temperature and pressure conditions to produce soft solid films of metallic chlorides, sulfides or phosphides. Sliding occurs on these soft, easily shearing films, thus protecting the base metal. When choosing the best EP additive for your needs, the most critical factors to consider are toxicity, performance, odor and ease of disposal. TPS From Elf Atochem TPS products are organic polysulfides which, when used in lubricant oil formulations, provide them with excellent extreme pressure properties. To ensure you get the best EP additive for your application, Elf Atochem offers four grades from which to choose: TPS 20,27,32, and 37. Each is suitable for use in neat and soluble oils.
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THIOTOPICS FROM ELF ATOCHEM TPS 37 can be emulsified in water without any problems. ksulfar Due to its high sulfur content 20 30 27 37 Spec, MiiL (37%), it is recommended for use in oil formulations workDi-tertiary Dkertiary Di
