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. 8, No. 1
PEL PLASTICS UPDATE
March-April, 2001
By Mort Wallach
ISSN 1094-656X

RECENT PROGRESS IN POLYMER/PLASTICS TECHNOLOGY
TECHNOLOGY & APPLICATIONS

Smart/Functional Polymers - High memory data-storage to 100-200 gigabytes per square inch was demonstrated with an array of scanning-probe microscope assemblies detecting tiny tailored indentations in poly(methyl methacrylate). The system has read/write capability and is expected to be commercial in 3-5 years. Also, a new suite of shape-memory polymers based on oligo(e-caprolactone)dimethacrylate and n-butyl acrylate were developed with potential use in medical and self-repairable applications.

• Peter Vettiger and Gerd Binnig at IBM’s Zurich Research Laboratory demonstrated the new high memory data storage device. Non-magnetic methods are being looked at to store data because magnetic disk technology is being continually reduced in scale such that in 3 - 4 years the disks would no longer store data (due to the super paramagnetic effect). The new device employs an array of 32X32 atomic force microscope (AFM) probes to make tiny indentations in the PMMA medium. The presence or absence of an indentation corresponds to 0s and 1s of digital data. Although each AFM tip reads and writes data relatively slowly by magnetic hard disk standards, with 1,024 assemblies operating in parallel the device may far exceed magnetic disk data-access rates in the near future. In this time-multiplexed parallel mode, 32 tips in a single row work in parallel, as each row is addressed in a time-orchestrated manner. For data to be written, heating elements beneath the tips warm them and soften a 50 nm thick PMMA storage medium. A small force applied to cantilever arms causes the tips to contact the polymer making tiny uniform sized indentations. Reading is done by scanning the tips across the surface with the heaters set in low power mode. As a probe dips into an indentation the heating element is cooled slightly by coming into close proximity to the polymer. The temperature change and hence the dent is sensed electronically. Data can be erased by warming the polymer causing it to flow into the indentations. The inventors say that commercial products can be expected in three to five years. First applications will likely be immobile devices such as cell phones or cameras that require small high capacity memory chips which consume little power. Vettiger and Binnig (1986 Nobel Laureate in Physics for inventing the scanning tunneling microscope) are very excited about this program. Clearly, PMMA tailoring could improve storage volume even further. (Appl. Phys. Lett. 77, 3299, 2000)

• Prof. A. Lendlein of the German Wool Research Institute and Prof. Bob Langer of MIT have developed a suite of shape-memory polymers with targeted use in stents, catheters, sutures. An additional market is self-repairable applications such as automobile fenders. The development is based on copolymers of oligo(e-caprolac- tone)dimethacrylate and n-butyl acrylate. The former furnishes the crystallizable switching segment that determines both the temporary and the permanent shape of the polymer. By varying the amount of the n-butyl acrylate comonomer the mechanical strength and transition temperature of the polymer can be tailored over a wide range. With one pair of comonomers one can have a whole set of shape-memory materials depending on the percentage of each present. For example one composition of this shape-memory copolymer converts from a temporary corkscrew shape to it’s parent linear shape in 45 seconds at 65C. Since homopolymers of each comonomer are biocompatible and biodegradable the way is opened to medical applications. This polymer system is easier to shape and offers more applications than the metallic shape-memory materials already in use such as the nickel-titanium alloy Nitinol. Marketing of these new polymeric products is being done by mnemoScience in Aachen, Germany. (Proc. Natl. Acad. Sci., 98, 842, 2001)

Lithography & Dendrimers - New DUV and E-beam chemically amplified resist materials were demonstrated based on dendrimer technology. Feature sizes were patterned well below 100 nm. Also, light harvesting dendrimers (like chlorophyll) are capable of quantitatively transforming light energy from their periphery to their core. Such systems could be used to convert solar energy into useful fuel.

• Prof. J. Frechet and coworkers at U. Cal. Berkeley have synthesized several new dendrimers which contain acid and thermally labile groups on their periphery. Tert-butyl ester and carbonate peripheral groups can be removed by acid catalyzed thermolysis which drastically changes solubility properties of the dendrimer. This forms the basis for a two-tone chemically amplified resist material-the first based on a dendritic polymer. This two tone system shows a high sensitivity towards both DUV and electron beam radiation. For example, using E-beam lithography pattern features well below 100 nm were obtained. Future work will include the optimiza- tion of resist formulations and patterning conditions. Also of interest is the performance of new dendrimer based resists, dendrimer-linear hybrids, and polymer composite resists, such as their dissolution behavior, cross linking and other factors. (Polymer Preprints, 41(1), 142, 2000)

• Prof. J. Frechet and coworkers at U. Cal. Berkeley and Eastman Kodak Co. in Rochester have shown that dendrimers based on laser-dye (Coumarin 2 and Coumarin 343) labeled poly(aryl ether) act as extremely efficient light harvesting antennae capable of transferring light energy through space from their periphery to their core. The light harvesting ability of these molecules increases with generation due to an increase in the number of principal chromophores. The energy transfer efficiency was quantitative for generation 1 to generation 3, with only a slight decrease observed for the fourth generation (to about 93%). Such systems are a potential solar energy source mimicing chlorophyll in natural processes. (Polymer Preprints, 41(1), 851, 2000)

Catalysis - Formation of patterned polymer films (e.g., norborene) on silicon and other substrates via surface initiated ring opening metathesis polymerization (ROMP) opens up possibilities for fabricating various features in microelectronic and MEMS devices. Also, one step polymerization of maleic anhydride/styrene block copolymer was achieved via nitroxide mediated living free radical techniques. Anhydride functionality is employed in many applications.

• Profs. G. Whitesides and coworkers at Harvard, N. Kim and coworkers at MIT, and Y. Haradas and coworkers at U. Illinois have demonstrated a method for growing thin polymer films from the surface of a silicon wafer having a natural oxide (Si/SiO2) by ROMP. Covalently attached norborene based polymer films were thereby grown by solution phase procedures. This reaction offers an ease of use and a control over the thickness and chemical composition of deposited films. The ability of the reaction to generate patterned polymer films on silicon and likely other substrates both in the plane and along the surface normal offers new possibilities for fabricating a variety of features in current microelectronic and MEMS devices. (Macromolecules, 33, 2793, 2000)

• C. Hawker and coworkers at IBM Almaden and T. Russell and coworkers at U. Mass/Amherst have applied living free radical methods to reactive monomers such as maleic anhydride using mixtures of a-hydrido alkoxyamine and nitroxide. The living nature of the polymerization is preserved in copolymerization with styrene leading to preferential consumption of maleic anhydride and the one step synthesis of functionalized block copolymer. Molecular weight can be controlled up to 100,000 while retaining low polydispersities. (Macromolecules, 33, 1505, 2000).

Alloys & Blends - Key property enhancements were obtained in polyketone/ethylene propylene (EP) copolymer blends by employing compatibilizers of both maleated EP copolymer and synergized by further addition of polyoxypropylene diamine as a crosslinking agent.

• E. Marklund and coworkers at the Royal Institute of Technology in Stockholm investigated the properties of polyketone/EP blends. Blends of EP copolymer and two polyketone grades with low and medium-high viscosities were prepared by melt extrusion. To obtain compatibility, a maleated EP copolymer was added to the blends. Polyoxypropylene diamine was also added as a crosslinker to some of the blends to further enhance compatibility. The blends were analyzed with differential scanning calorimetry. In a second step the blends were compression or injection molded. SEM, shear viscosity, density measurements, IR spectroscopy, were used to characterize the molded blends and their oxygen permeabilities were assessed. Impact strength and hardness were also measured on injection molded blends. It was shown that the oxygen barrier properties of the EP copolymer could be greatly enhanced by a small addition of the low viscosity polyketone. A content of 23.9% by volume of polyketone was sufficient to lower the permeability by 70% compared to pure EP copolymer. The incorporation of polyoxypropylene diamine had a profound effect on the morphology. The polyketone particles in this case were small, and the absence of “pull-outs” suggested an enhanced phase adhesion between the different components. Further the incorporation of polyoxypropylene diamine had no affect on the oxygen permeability but the impact toughness and hardness were increased and the shear viscosity was also increased in its presence. This indicated an enhanced system compatibility brought about through an amine/anhydride reaction. (Polymer, 42(7), 3153, 2001)

Alloy & Blend Patents - Among 1000 patents reviewed during this period, there are several noteworthy inventions involving: production of nanocomposites with multi- layered silicates and various polymers, new acrylic modified organopolysiloxane thermoplastic elastomer compositions, and fabricating fluoropolymer/liquid crystal polymer composite articles.

• "Process For Production Of Nanocomposite Polymers". C-J. Chou et al (Dow Chemical Co.) PCT Int. Appl. WO 00 29,467, May 25, 2000. Title process comprises mixing a polyvalent anionic organic edge coated quaternary ammonium intercalated multilayered silicates (MS) with a thermoplastic polymer (A1) at a temperature above the melting point or softening temperature of the A1, or mixing MS with a monomer and polymerizing the system. Preferably, the above polyvalent anionic organics are polyacrylates. Preferable, the use of polar substituted quaternary ammonium compound in the above MS should accompany with polar polymers e.g., polyureth- anes or nylons; while nonpolar quaternary compound should accompany relatively nonpolar polymers e.g., polyolefins. (Chem. Abs. 132: 335420p)

• "Olefinic Thermoplastic Elastomer Compositions". N. Noda (Shin-Etsu Polymer Co.) JP 2000 143,884, May 26, 2000. The olefinic thermoplastic elastomer (TPE) compositions contain 1-100 phr acrylic-modified organopolysiloxanes and 0.01-5 phr stearic acid (I) and/or higher fatty amides. The compositions offer moldings free from bleed out and having excellent sliding property and resistance to abrasion and scratch while keeping elongation and elasticity. Thus, a composition comprising Milastomer 7030N (TPE), 10 phr acrylic-graft organopolysiloxane (Chaline R 1), and 0.5 phr F 3 (I) was kneaded at 160°C, and molded to give a roll sheet, and pressed between plates to give sheets having no bleed-out after 800 h of weathering test, static friction coefficient 0.25 mm, dynamic friction coefficient 0.08 mm, tensile strength 7.2 MPa, elongation 450%, and good friction and abrasion resistance. (Chem. Abs. 132: 348870k)

• "Method of Fabricating Composite Fluoroplastic Articles". J. C. Lee et al (DuPont-Mitsui Fluorochemicals Co.) Eur. Pat. Appl. EP 1,086,987, March 28, 2001 A method of fabricating composite fluoroplastic articles is described which method comprises the steps of melting and blending together a melt-processable fluoro- polymer and a liquid crystalline polymer having a melting point of at least 20°C higher than that of the fluoropolymer, orienting the blend so as to form molding particles comprised of liquid crystal polymer dispersed in a fibrous form within a fluoropolymer matrix, then melt processing the particles at a temperature of at least the melting point of the fluoropolymer but not above the melting point of the liquid crystal polymer. Composite articles manufactured by this method have good moldability, low linear expansion coefficient, and molding shrinkage, and excellent strength and deflection temperature. Thus, 90% PF 004 (fluoropolymer) and 10% Zenite 7000 were thoroughly dried and extruded to give a test piece showing melt viscosity at 345°C 3750 P (375 Pas), tensile strength 190 kg/cm2 (18.6 MPa), elongation 33%, tensile modulus 4200 kg/cm2 (412 MPa), and linear expansion coefficient 2.5 x 10-5/°C. (Chem. Abs. 134: 267063p)

New Polymer Ventures - DuPont’s iTechnologies and the Rohm and Haas subsidiary Shipley (a photoresist maker) formed a joint development team to establish the enabling technology for the next generation of semiconductor chips. A key goal is to bring fully formulated 157 nm photoresists and antireflective coatings to the marketplace by 2003. Shipley will contribute it’s photoresist expertise and will license DuPont’s fluoropolymer binder resin technology. In the past few years the materials used in microlithography have been undergoing dramatic change. More transistors are being crammed onto chips and the features are getting smaller. As a result the polymers used in the process must be sensitive to shorter wavelengths of UV light (i.e., DUV). The photoresists and antireflective coatings which DuPont and Shipley are targeting will allow features of 70 nm which could more than triple the number of transistors on a chip. (C&EN, Jan. 22, 2001, p. 19)