PEL PLASTICS UPDATE highlights recent progress in key areas of polymer/plastics technology including: catalysis, biopolymers, smart/functional polymers, alloys & blends, nanotechnology, polymer modification and new ventures. A recent issue of PEL Plastics Update follows.

Vol. 7, No. 5
PEL PLASTICS UPDATE
Sept.-Oct., 2000
By Mort Wallach
ISSN 1094-656X
 

Nanotechnology-New ordered arrays of inorganic cores in thin polystyrene (PS) film were developed via attachment of initiator for atom transfer radical polymerization (ATRP) to the surface of a silica nanoparticle, and subsequent polymerization from the surface. Potential array applications include diffractive optics, electro-optical devices, information storage, and tailored composites. Also, electric fields were found to orient nanoscopic domains laterally in thin films of block copolymers offering potential applications as lithographic templates.

• T. von Werne and coworkers at U. Cal. Davis and M. Ellsworth and coworkers at Raychem in Menlo Park prepared structurally well defined polymer nanoparticle hybrids by modifying the surface of silica nanoparticles with initiators for ATRP and by using these initiator modified nanoparticles as macroinitiators. Well defined polystyrene chains were grown from the nanoparticle surface to yield individual particles comprised of a silica core and a well defined polystyrene outer layer. When cast from solution, the hybrid nanoparticles formed domains in which the inorganic cores were evenly dispersed throughout the polymer matrix and displayed a hexagonal ordering. These organized structures can exploit the novel magnetic, optical and material features of the nanoparticles. Potential applications of these ordered arrays of nanoparticles include diffractive optics, electro-optical devices, information storage, and tailored composites. (PMSE, 82, 233, March, 2000)

• T. Russell and coworkers at U. of Mass. Amherst and H. Jaeger at U. of Chicago have shown that electric fields are an effective means of orienting copolymer domains (i.e., PS/ PMMA) normal to an interface. A thickness independent field strength was found at which full alignment of the cylinders parallel to the field lines occurred. This threshold field strength is directly related to differences in the interfacial energies of the components. Slightly below this threshold a coexistence of parallel and perpendicular alignment of the cylinders was found, resulting from the competition between the applied field and interfacial interactions. The studies herein demonstrate the precise nature by which nanoscopic structures in thin films can be manipulated by the interplay of passive and active fields. The resulting structures, i.e., thin films containing arrays of nanoscopic cylinders oriented normal to the substrate, are promising candidates as templates for a variety of nanostructures. (Macromolecules, 33, 3250, 2000)

Smart/Functional Polymers- Novel electro-optic chromophores are leading to a revolution in telecommunications and information processing. Possibilities include elimination of the lengthy download time on the internet when transferring digital data onto fiberoptic transmission lines, replacing lithium niobate in electro-optic modulators in certain high speed applications, and semiconductor electronics producing compact highly sophisticated opto-chips for very powerful computers. Polymer modulators can usher in new applications such as instantaneous 360° radar for aircraft navigation and collision avoidance in automobiles.

• L. Dalton and coworkers at USC and B. Robinson at U. of Washington, Seattle have embedded an electro-optic chromophore (CLD-1) with an isophorene center moiety in a polymer matrix achieving operational voltage of only 1 volt. The system is thereby capable of encoding information from electrical signals into optical transmissions at 110 gigahertz- which is equivalent to 110 billion bytes/sec. This could eliminate the lengthy download time on the internet resulting from the bottleneck caused when transferring digital data onto fiberoptic transmission lines. Thus the potential in certain high speed applications to replace lithium niobate (LiNbO₃) currently used in electro-optic modulators. Such new polymer modulators by virtue of their greater speed, lower voltage, and smaller size, weight and price can usher in new applications such as new instantaneous 360° radar for aircraft navigation and collision avoidance in automobiles. These modulators would allow direct integration and semiconductor electronics producing compact highly sophisticated optochips for very powerful computers. Since an applied voltage causes a change in a materials refractive index, light can be switched from one path to another; this phenomena allows a modulator to encode information onto laser beams by modulating the amplitude. A key to this discovery was the finding that minimization of electrostatic interactions can be achieved by making the chromophore ellipsoidal in shape. Work at Lockheed Martin also achieved similar speeds using a thiophene center moiety instead of isophorene. Current work with chromophores containing dendritic groups yielding a spherical symmetry more than doubles electro-optic activity and thereby requires even lower drive voltages. (Science, 288, 119, 2000)

Fuel Cells-New PEM fuel cell membranes which overcome Nafion (perfluoronated ionomer) deficiencies of temperature limitations (80C max) and high cost were developed employing sulfonated polyimides. These polymers have a unique combination of properties including excellent thermal and thermooxidative stability, mechanical and electrical properties, and outstanding chemical resistance.

• J. E. McGrath and N. Gunduz at Virginia Polytechnic have synthesized fuel cell membrane candidates from a series of high molecular weight five membered ring polyimides containing sodium sulfate groups using 2,5-diamino benzene sulfonic acid monomer. Tough, creasable films were obtained for polymers with lower sulfonation levels (determined by acid-base potentiametric titration). Solution cast films of the sulfonated polyimide membranes demonstrated moderate to high water absorption which is necessary for PEM fuel cells. Further work is underway with six membered imide systems with greater stability and with sulfonated polyarylene ethers which also have superior properties. (Polymer Preprints, 41(1), 182, 2000)

Alloy & Blend Patents-Among 1500 patents reviewed during this period, there are several noteworthy inventions involving: plastic optical fibers of norbornene resin core/polyolefin cover (Jsr/JP patent), foams of alkenyl aromatics with increased HDT (Dow/U.S. Patent), weatherable blends of polyester/PC block copolymers and their blends (GE/WO Patent), and fluorinated polybenzoxazoles with high T_g and low dielectric constant (U.S. Air Force/U.S. Patent).

• "Plastic Optical Fibers Made Of Norbornene Resin Cores With Polar Group-Containing Polyolefin Covers". K. Kubota et. al. (Jsr Co., Ltd.) JP 2000 109,743, April 18, 2000. Title optical fibers with environmental stability under high-temp and moisture conditions are prepared from norbornene resins covered with polar group-containing polyolefin copolymers. Thus, a 1 mm plastic fiber composed of a hydrogenated norbornene resin core prepared from 8-methyl-8-methoxycarbonyltetracyclo-[4.4.0.1^2.5.1 ^7.10]-3-dodecene and 1-hexene, and a cladding made of poly(Me methacrylate) and poly(vinylidene fluoride), was covered with 0.2mm ethylene vinyl alcohol copolymer (Eval EP E105) and 0.4 mm polyolefin blend of polypropylene-ethylene-propylene copolymer (Santoprene 251-92) and maleated polypropylene (Youmex 1001), showing no sticky phenomenon for a 100 hour test at 85°C/85% humidity. (Chem. Abs. 132: 280206r)

• "Foams Having Increased Heat Distortion Temperature From Blends Of Alkenyl Aromatic Polymers". B. Chaudhary et. al. (Dow Chemical Co.) US 6,048,909, April 11, 2000. The present invention pertains to improved alkenyl aromatic polymer foams (and processes for their preparation) having increased heat distortion temperature and improved dimensional stability while maintaining good tensile/tear, creep and environmental dimensional change properties. The closed cell low density alkenyl aromatic polymer foams exhibit increased heat distortion temperature, when substantially random interpolymers of about 21 to about 65 mol% styrene are blended in. The foams contain alkenyl aromatic polymers and copolymers of vinyl aromatic monomers and/or vinyl cycloaliphatic monomers and -olefins. When these same alkenyl aromatic polymer foams are made without these interpolymers, the heat distortion temperature is not improved. A blend contained polystyrene and ethylene-styrene copolymer [prepared using (1H-cyclopenta[1] phenanthrene-2-yl)dimethyl(t-butylamido)-silanetitanium 1,4-diphenylbutadiene catalyst].(Chem. Abs. 132: 280158b)

• "Weatherable Polyester-Polycarbonate Block Copolymers And Blends Containing Them". T. Siclovan et. al. (General Electric Co.) PCT Int. Appl. WO 00 26,274, May 11, 2000. The block copolymers comprise organic carbonate blocks alternating with arylate blocks derived from resorcinol and >1 aromatic dicarboxylic acids (e.g., isophthaloyl chloride and terephthaloyl chloride). The block copolymers are blended with other polymers such as polycarbonates and poly(alkylene carboxylates) to improve the weatherability. Thus, resorcinol reacted with isophthaloyl chloride and terephthaloyl chloride in the presence of tetra(n-butyl)ammonium bromide to form the hydroxy terminated polyester intermediate having M_w 19,200 and M _n 9,500 and then mixed with bisphenol A and phosgene to give a block copolymer with M_w 73,000. (Chem. Abs. 132: 309178w)

• "Fluorine-Containing Polybenzoxazole-Type Polymers With High Glass Transition Temperature And Low Dielectric Properties". F. Arnold et. al. (The United States of America as Represented by the Secretary of the Air Force) US 6,057,417, May 2, 2000. The polymers are prepared by polycondensation of 2-hydroxyterephthalic acid (I) or 2,5-dihydroxyterephthalic acid with 2,2-bis(3-amino-4-hydroxyphenyl)hexafluoropropane (II) in polyphosphoric acid. Copolymers are prepared in a similar way using ,2-bis (4-carboxy-phenyl)hexafluoropropane as the coacid monomer. The polymers exhibit a high glass transition temperature (T_g) and a low dielectric constant and are useful for microelectronic packaging. Thus, 10 mmol of I and 10 mmol of II were polycondensed in 34.21 g of 83% PPA to give a polymer with T_g 426(C, moisture uptake <0.2%, dielectric constant 2.38, and good thermooxidation stability. (Chem. Abs. 132: 308854b)

Dendrimers and Hyperbranched Polymers-Hyperbranched polyester templating agents for producing nanoporous organosilicates provide low dielectric constant (~2.0) materials for use in DUV lithography.

• D. Mecerreyes and coworkers at IBM Almaden, San Jose have developed a general approach to nanoporous silicates in the pursuit of new low dielectric constant insulating films. Hyperbranched polyesters prepared in one step with abundant chain end functionality and increased solubility facilitated compatibilization of the polyester/MSSQ silicate (methylsilsesquioxane) mixture on a nanoscopic scale. In contrast to previously surveyed star-shaped polycaprolactones the hyperbranched materials were incorporated in the MSSQ matrix at higher loading levels and resulted in smaller pores. The porous films generated by thermolysis of the hyperbranched polyesters have low refractive indices and dielectric constants (as low as 2.0 @ 30% porogen) which depend on the porogen content in the initial hybrids. (Polymer Preprints,41(1), 517, 2000)

Environmental- Effective disposal of waste polymeric materials was demonstrated in the polypropylene-EPDM rubber (ethylene-propylene-diene-monomer) system commonly used in automobile bumpers and other automotive parts. Current disposal methods include pyrolysis and reformation of polymer, however these methods have had limited success. The depolymerization of a polypropylene-EPDM mixture via supercritical water partial oxidation provides a potential method to dispose of these automobile bumpers while recovering monomer, oligomer and other hydrocarbons.

• A. Crow and coworkers at U. of Missouri-Columbia developed a novel process dealing with the depolymerization of the PP/EPDM system via supercritical water partial oxidation. This process offers the advantages of recovery of monomer, oligomer and other useful hydrocarbons in a short reaction time and with high efficiency. The process offers a new avenue not only for disposing of waste polymers, but more important for facilitating environmentally sound recovery of monomers that can be made available as raw materials in the petrochemical industry. Experiments were carried out in a one liter Hastelloy-C276 bolt closure reactor with a 25% EPDM/75% PP system. Key issues investigated are the product yield, and in particular the selectivity towards propylene and ethylene monomers. The process parameters studied include the amount of oxygen in the feed and reaction time, as well as the reaction temperature and pressure. (Div. Environ. Chem. Preprints, 40(1), p. 1, 2000)

New Materials/Biotechnology Venture-DuPont and MIT have formed a five year $35 million R&D alliance in the field of biologically enhanced materials. They expect it will help the company establish a path to its long term materials and biotechnology goals. The steering committee is chaired by DuPont's chief science and technology officer Joseph Miller and Robert Brown provost and Prof. of chemical engineering at MIT. The first projects were scheduled to get under way in the fall of 2000. Proposals were submitted from departments including: Sloan School of Management, nuclear engineering, biology, chemistry and materials science. Teams include both DuPont and MIT researchers with funding up to $1.5 million/year and $100K for speculative ideas. Projects will center on fundamental science of biobased materials and technologies which could include fine chemicals, monomers, biopolymers, and biomodified polymers. Another area is bioelectronics including anything from sensors that detect biological molecules to molecular electronics based on biological systems. Materials with biomedical applications are also being considered. DuPont management feels that there is great potential for applying biology to the materials business. They will retain rights to an exclusive license tied to any patents that result from the research; MIT will retain a nonexclusive license to the patents for research purposes. DuPont is interested in ways to tweak existing microorganism metabolic pathways so an organism will make a desired product such as a polypeptide or polysaccharide at a rapid rate. With the know-how to quickly commercialize routes to new materials (e.g., monomers) DuPont would consider licensing the knowledge. (S. Wilkinson, C&EN, June 5, 2000, p. 31)