elude lower sulfur dioxide and carbon dioxide emissions/' An industry working group with about six members has formed to help develop the technology. Another cooperative venture, focused on green cleaning technology using supercritical fluids to replace chlorofluorocarbons, was described by Dennis L. Hjeresen, program manager of applied environmental technologies at Los Alamos National Laboratory in New Mexico. Many efforts aimed at "green" technology are under way (C&EN, Sept. 6, page 26) at Los Alamos. The lab has established a user facility where companies can test cleaning technologies on real parts and equipment. Hjeresen says the facility now has a 60-L system running, the largest commercially available for supercritical fluid cleaning. By means of a piezoelectric sensor installed in the cleaning system, in-situ measurements of contamination removal can help determine appropriate end points for the supercritical fluid cleaning process. Membranes, too, are receiving increased attention for use in material recovery processes and pollution control. One example, described by Rod Ray of Bend Research, Inc., Bend, Ore., deals with a new type of reverse osmosis membrane for treating oily wastewaters. "Strict new government regulations pertaining to the discharge of oily wastewaters represents a significant technical and economic challenge for today's oil producers," says Ray. "Between one and 100 barrels of wastewater are typically produced per barrel of oil. This ... waste stream can contain oil and grease, dissolved organics, dissolved solids, and suspended solids. ... [The] majority of these contaminants must now be removed prior to disposal." The company has patented a special hollow-fiber membrane module that "exhibits exceptional resistance to fouling," says Ray. Feed solution is pumped through the insides of the hollow fibers. Purified water, which can be discharged or reused, passes through the fiber walls, while a concentrated solution of contaminants for disposal or recycling exits the ends of the fibers. By applying special coatings to the inside surfaces of the hollow fibers, the company can tailor membrane performance to particular applications. These include feed streams with high concentrations of organics or dissolved solids or those having high osmotic pressures. •
Groups report on advanced polymers
Cyclic oligomers form nonlinear optical resins
Μ'ΙΓ.»^.! Stephen C. Stinson, C&EN Northeast News Bureau Widespread efforts aimed at syntheses of advanced polymers are continuing to bear fruit. Although based on costly raw materials or employing complex processes, new polymers resulting from advances discussed in Chicago could be economically viable as parts of technology systems, if not on a cent-per-poundof-resin basis. Among the advances: • Organic chemistry professor David E. Bergbreiter of Texas A&M University, College Station, described a polymeric "smart" hydrogénation catalyst to the
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SCIENCE/TECHNOLOGY Division of Organic Chemistry that acts at low temperatures but loses activity at higher temperatures. Such a catalyst might function to prevent reactions from running away by automatically slowing or shutting down. • Ring-opening polymerization of cyclic oligomers was the method used by graduate student Joseph J. Kulig to make polycarbonate resins with unusu al optical properties at the University of Akron, Ohio. Such polycarbonates with inherent nonlinear optical proper ties, Kulig told the Division of Polymer Chemistry, might be fabricated into useful objects that do not depend on unstable molecular orientations of low molecular weight crystals or additives. • Polycarbonate block copolymers with polyether sulfones were the sub ject of two reports by chemists Robert J. Kumpf and Wolfgang Kaufhold of Miles' polymer division, Pittsburgh, to the Division of Polymer Chemistry. Miles is the former Mobay Corp. and the U.S. subsidiary of Bayer. Block co polymers like these might be used as engineering thermoplastics with valu able combinations of the properties of each homopolymer. They might also serve as compatibilizing additives in blends of polycarbonate and polyether sulfone homopolymers. • Polyaryl ketones are also valuable engineering thermoplastics, and a nov el way to get around the difficult pro cessing of these was detailed by gradu ate student Ashish Pandya of Virginia Polytechnic Institute & State Universi ty, Blacksburg, to the Division of Poly meric Materials: Science & Engineer ing. The Virginia Tech approach is to make soluble precursor resins that are easily convertible to polyaryl ketone sulfone-type plastics. The smart hydrogénation catalyst of Texas A&M depends on what is called the inverse temperature-dependent solubility of the resin used to make it. Most resins increase in solubility as temperature increases. But the polyethylene oxide (PEO)-polypropylene oxide (PPO) block copolymer that Bergbreiter uses decreases in water solubility as temperature rises. The reason for this solution behavior is unclear but may arise from entropy-related changes in polymer chain conformation that make the resin increasingly hydrophobic. Working with postdoctoral fellow Li Zhang and graduate student Vimala M. Mariagnanam, Bergbreiter oxidized 38
SEPTEMBER 13,1993 C&EN
High-temperature resins made by novel route
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the primary terminal hydroxyl groups of PEO-PPO-PEO to carboxyl groups. The researchers then converted them to acid chlorides, which reacted with bis(2,2-diphenylphosphinoethyl)amine to put two diphenylphosphino groups at each chain end. Treatment of the resulting resin with a rhodium(I) complex resulted in the resin-bound rhodium catalyst. Like the parent PEO-PPO-PEO resin, the rhodium-bound form is water soluble and is an effective hydrogénation catalyst at 0 °C. At 40 to 50 °C, however, water solutions cloud up as the resin comes out of solution, and hydrogénation stops. Solubility and catalytic activity are restored on cooling again to 0°C. As an application of the phenomenon, Bergbreiter and his coworkers imagine an exothermic reaction in which the catalyst deactivates above a certain temperature. In case the reaction starts to take off, the catalyst deactivates, and the reaction cannot continue until the temperature subsides below the threshold limit. The nonlinear optical resins studied
at Akron have potential uses in electrooptical switching, as light passing through them is modulated by an electric field. They may also extend usefulness of laser beams by converting them to light of half the wavelength. Such inorganic crystals as lithium niobate have nonlinear optical properties. This salt is routinely used, for example, to convert near infrared light at 1064 nm from a neodymium-YAG (yttrium-aluminum garnet) laser to a visible beam at 532 nm. But these crystals are mechanically brittle and hard to make into useful objects. Researchers would prefer a thermoplastic resin with nonlinear optical properties that could be fashioned at relatively low temperatures. Molecules of such a substance need a combination of functional groups that imparts what is called high hyperpolarizability, a measure of a molecule's interaction with light. The molecules must also be oriented in a nonsymmetrical manner, so that hyperpolarizabilities do not cancel one another out, and so that the bulk substance does have what is known as a high second-order
susceptibility, a measure of a bulk sub stance's interaction with light. The resin described by Kulig con tains the hyperpolarizable grouping 2-(4-nitrophenyl)oxazole. The oxazole ring is further substituted with 4-hydroxyphenyl groups, which could let the molecule be incorporated into poly carbonate chains with bisphenol A. Working with polymer chemistry professor William J. Brittain, Kulig used polymerization of cyclic oligo mers to make polycarbonates incorpo rating the oxazole group. Originally developed by chemist Daniel J. Brunelle at General Electric, this technique begins with preparation of cyclic oligo mers containing rings of three to 20 bisphenol A carbonate sequences. The relatively low molecular weights of cyclic oligomers impart low melting points, so they are thin, easily castable syrups at 100 °C. Yet such anionic initia tors as titanium diisopropoxide bis(acetylacetonate) spark opening of rings to short chains with reactive ends, which in turn can attack and open other rings, building up polycarbonate chains with molecular weights as high as 300,000. Kulig and Brittain made such bisphe nol A carbonate cyclic oligomers con taining 13% of the bis(4-hydroxyphenyloxazole). While a l-μιη film of the melt was curing, they applied an electric field of 100 volt per μιη to orient the oxazole groups for high second-order suscepti bility. The resulting cured films have molecular weights of only 6400 to date, but they do have nonlinear optical prop erties. In future research, the Akron group hopes to increase molecular weights and improve film formation and electric field orientation. Ease of processibility is the aim of Pandya at Virginia Tech. But instead of nonlinear optical properties, Pandya seeks routes to unique engineering ther moplastics. Working with chemistry professor Harry W. Gibson, Pandya's approach is synthesis of soluble and more tractable resins as precursors to the high-temperature resins they want. The chemists begin by converting aro matic dialdehydes to aminonitriles. For example, reaction of terephthalaldehyde or isophthaldehyde with morpholine and sodium cyanide gives quantitative yields of aminonitriles. The cyano groups on each aldehyde carbon atom render the hydrogen atoms there acidic. Deprotonation with sodium hydride in dimethylformamide results in dianions,
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SEPTEMBER 13,1993 C&EN
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"Your Partner In Innovation: Eastman Fine Chemicals" Intermediates Available In Large Quantities 0-(4-Nitrobenzyl) Hydroxylamine Hydrochloride 02N — /
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2,4-Dichlorophenacyl Chloride ci —Ρ
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4-Methoxvphenacyl Chloride MeO — &
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Methyl 4-Formylbenzoate Ο Η
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4-Formylbenzoic Acid Ο
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CIRCLE 38 ON READER SERVICE CARD 40
SEPTEMBER 13,1993 C&EN
SCIENCE/TECHNOLOGY which form a soluble polymer by displacing halogen atoms from bis(4fluorophenyl) sulfone at moderate temperatures in 99% yield. These soluble, intermediate, aminonitrile-based resins can be converted to insoluble polyphenylene ketone ketone sulfones by hydrolysis in 30% aqueous acetic acid. Pandya emphasizes that this combination of a p- or m-phenylene, two keto, and one sulfone grouping is unique in the annals of engineering thermoplastics. And, Pandya says, the melting point of the p-phenylene resin, 414 °C, is the highest reported to date among polyaryl ketones. Kumpf and Kaufhold of Miles' polymer division also seek polymers with multiple types of recurring groups, both as high-temperature thermoplastics in their own right and as compatibilizers for blending homopolymers. The Miles target compatibilizer takes the form of polycarbonate-polyether sulfone block copolymers. Working with chemists Richard Archey, A. Donald Meltzer, Harald Pielartzik, and Kaufhold, Kumpf has developed what he calls "wet-side" and "dry-side" approaches to such copolymers. By wet-side, Kumpf means traditional polycondensation of monomers in solution. Dry-side refers to polytransesterification of precursor resins in a melt. The Miles team favors the dry-side approach, because chemists are familiar with properties and handling of polycarbonates and polyether sulfones already available and so do not have the problems of developing a whole new resin class. Working with known materials thus also shortens the product development cycle. For their polyether sulfone, the Miles researchers condensed bisphenol A, bis(4-fluorophenyl) sulfone, and p-hydroxyphenyl p-hydroxybenzoate. The polyether sulfone of commerce contains only bisphenol A and diphenyl sulfone units. The third monomer added in this work furnishes a phenyl benzoate ester grouping that can be transesterified with the bisphenol A polycarbonate that they also use. Kaufhold described work with chemists Kerstin Grobler, Kumpf, and Meltzer at Miles, and chemical engineering professor Robert E. Cohen, postdoctoral fellow Michelle Hutnick, and graduate student Cora Dancy at Massachusetts Institute of Technology to test the compatibilizing agent. Π
