Summary Record of the Workshop on Polymer Materials Research: August 30-31, 1999, Woods Hole, Massachusetts (2000)

Discussions were conducted in five specialized topic areas:

• polymers for space applications

• functional polymers

• accelerated development and commercialization methods

• future trends/opportunities

• polymers for structures

Each session began with an introductory presentation and was followed by brainstorming sessions to identify future areas for research and barriers that would have to be overcome.

Barry Farmer (AFRL/ML) presented background information on space polymers. He echoed Dr. Browing's opinion that the Air Force is in transition from an air force to a space force. The key motivations for this transition are: (1) improving reconnaissance capabilities (global vision), (2) projecting power, and (3) providing advanced capability for energy conversion and storage.

Farmer described several opportunities for key enabling developments in polymers with space applications:

Farmer challenged the workshop to consider ways to meet the goal of reducing both cost and weight of space structures by 50 percent by 2010. An example of an application for improved structural materials would be tethers used to move objects from low orbit to high orbit. These tethers would be up to 300 km long and would require very high strength and reliability. Tethers would also have to be electrically conductive and “reelable.”

Gossamer materials have a very large area and are very lightweight (e.g., 10,000 to 40,000 sq meters with a density of 1.5–10 g/m². R&D would be focused on lightweight materials, stability in space environments, and resistance to punctures and tears.

Large deployable space structures would require passive, net-shape films, active shape control for films, and optical coatings with durability and survivability in space environments.

The key areas for polymer R&D for payloads are membranes, mirrors, optics, optical coatings, polymer microelectromechanical systems (MEMS), and electrically conductive polymers.

Other uses for polymers include polymers for hyperspectral imaging, consumable polymers (e.g., using excess structure after launch for fuel because most of the strength in a space structure is needed to survive the launch, not for operation in orbit), space-based optics and lasers, space-based radar (i.e., low-mass, high specific-power generation, very lightweight antennas), and power generation (e.g., advanced batteries, photovoltaics, solar concentrators, and flywheels).

Workshop participants identified the following specific research opportunities for polymers for space applications:

• processing/repair in space

• performance prediction in space environment

• processing/structure/performance relationships and optimization for carbon nanotubes (i.e., nanostructurally controlled nanotubes)

• processing/structures/performance relationships and optimization for ceramic precursor polymers for composites or coatings

• new ways to fabricate multilayer, multifunctional polymers

• polymerization in space (templated polymerization)

• detection and repair in space—self-healing devices (MEMS spiders)

• processing/structure/property relationships for structural polymers as fuels

• use of photodegradation processes for energy propulsion

• development of biomimetic systems (e.g., consumable, self-healing, energy conversions)

• development, characterization, and scaling of polymers for radiation protection

• characterization of degradation of electrically conductive polymers

Workshop participants identified the following barriers to the development of polymers for space applications:

• difficulties of designing for use in extreme thermal and other environmental conditions

• lack of awareness of ground-based testing facilities

• the difficulty of understanding and developing mechanisms in the specified time frames

Arthur Epstein (Ohio State University) provided introductory material on functional polymers and described some of their promising applications. He categorized functional polymers in terms of their functionality:

• electrical function (insulators, semiconductors, and metallic conductors)

• optical function (nonlinear optics, lasers, and optical communications)

• magnetic function (ferromagnetism, photoinduced magnetism, high coercivity, and magnetic shielding)

• chemical function (sensors, actuators, processing, and corrosion protection)

He pointed out that polymers with electrical function are being used commercially (e.g., Philips has commercialized light-emitting diodes). The other remaining functional applications are in the earlier stages of the R&D cycle or do not have sufficient industrial interest for commercialization.

Dr. Epstein identified a number of technological issues he thought should be addressed to determine the potential of functional polymers:

• processing methods to achieve ultimate properties

• constituents with sufficient chemical purity

• control of molecular weight

• determination of ultimate functional capabilities

• incorporation of smart and nanoscale functions into polymers

• competitiveness with alternative materials

Workshop participants identified the following opportunities for R&D on functional polymers:

• improving methods of establishing and measuring the chemical purity of polymers

• developing a methodology for supermolecular synthesis (“clean” synthesis)

• understanding and using structural and organizational/anisotropy

• using modified proteins for biomimetic functions

• understanding the role of polymer/polymer interfaces (also polymer/metal and polymer/inorganic interfaces) in the fabrication of multilayer devices

• combining materials to achieve multiple functions (e.g., adding mechanical function to electromagnetic or chemical function via block copolymers, interpenetrating networks)

• using tethered initiators to “grow” coatings

• using and optimizing surface controls for fabricating multilayer functional polymers

• developing processes to control property gradients in functional polymers

• applying combinatorial methods to investigate new materials

Workshop participants identified the following goals for promising applications:

• processible, stable polymer magnets/films for space applications

• controlled polymer electroluminescence for flexible displays

• conductive polymers with conductivity greater than copper in polymers

• functional properties that can be tuned in real time in response to the use environment

• smart magnet materials (e.g., photoresponsive magnets)

• polymers with chemical or electromagnetic function for sensing (e.g., chemical sensors, corrosion sensors)

• molecular-level electronics (e.g., switching)

• polymer single-electron devices

• conductive polymer welding/brazing for large apertures

Edwin Thomas (Massachusetts Institute of Technology) introduced the subject of accelerated development and commercialization. He pointed out that polymer science, especially for high-performance polymers, has been in a technology-push mode and suggested that supramolecular chemistry has driven most of the recent advances in polymers. He pointed out that recently the “lone wolves” of university research have given way to “team-based” research involving many students (graduate and undergraduate), visiting scientists, and partnerships with government and industry. Therefore, success now depends on assembling teams with the optimum mix of skills and experience.

One workshop participant pointed out that this approach deemphasizes curiositydriven research. Another noted that venture capital is becoming an important mechanism for university funding via small business strategic partnerships and that the challenge is to promote creative designs that use novel materials and processes.

Ruth Pachter (AFRL/ML) introduced an idea that the Air Force has been developing to establish a center for accelerated maturation of materials. The center would focus on modeling and simulation and computational tools to reduce the requirements for physical testing in an exploratory research program. The center would complement other efforts by the U.S. Department of Defense (DOD) to modernize high-performance computing capabilities. The challenge will be to understand structure/property relationships and develop algorithms that span the hierarchy of scales, from molecular to macro scales.

Finally, Leslie Smith (National Institutes of Standards and Technologies [NIST]) reviewed NIST's R&D on combinatorial methods for materials to provide a means of screening a range of compositions and characterization methods very quickly. The program is being driven by industry's desire to accelerate and reduce the cost of R&D. Combinatorial methods are being used in industry to develop large databases. The chemical industry has been especially active in this area. A workshop participant pointed out that these methods are most applicable to the early phases of research and that the development of data libraries has been a difficult process. Another participant pointed out that, when used for discovery research, combinatorial methods make it easier to miss the importance of serendipitous results.

Workshop participants identified the following opportunities:

• more emphasis on team-based research, with a variety of disciplines represented

• more emphasis on externships (i.e., researchers working in industry to gain practical experience)

• the development of mechanisms to bring researchers into closer contact with customers

• the promotion of creative designs based on novel materials/processing

• the use of entrepreneurial models for university researchers (e.g., spin-off companies)

• the development of data libraries in polymer science by using combinatorial methods

• the development of nanoscale physical property measurements

Workshop participants identified the following barriers to accelerated development:

• potential conflicts of interest

• concerns about protecting intellectual property and nondisclosure

• potential that directed research might lure people away from exploratory research

In his introduction, Douglas S. Dudis (AFRL/ML) explained that developments in technology could change Air Force doctrine. The focus of his remarks was on how AFRL should encourage forward-looking, fundamental research and innovative technology development that reach beyond the requirements for near-term systems. In Dudis' opinion, the Air Force should continue to nurture research, even though it can no longer sponsor all of the research believed to be important.

Some workshop participants expressed concerns that the changing role of AFRL in R&D and application of new materials will inhibit innovation. The question was raised about where new materials advances, such as the 40-year coatings the Air Force needs, would come from.

Workshop participants identified the following goals for the AFRL program:

• leveraging of computational methods from other programs

• the development of standards for interactions among research partners

• the development of mechanisms for communicating priorities to researchers

• improving the process for the scale-up and transfer to industry of new functional polymers

• the nurturing of interactions between synthetic chemists and “characterizers”

Workshop participants identified the following research opportunities:

• the development of fundamental theory for many-body problems and molecular mechanics

• the development of extended time scales for modeling

• the development of predictive methods for properties

• the development of isotropic, 3-D polymers similar to diamonds

• the development of quasicrystal coatings

• the development of new syntheses for monomers and polymers (e.g., supramolecular structure)

• the development of new techniques for characterizing supramolecular structure (e.g., atomic force microscopy, nuclear magnetic resonance)

• the development of microblock polymers

• the development of polymers that act as transducers

• the addition of functionalized groups to block copolymers

Workshop participants identified the following barriers to pursuing innovative research:

• Security measures could inhibit interactions (e.g., DOD high-performance computing resources, which are behind security firewalls, are not available to outside researchers).

• Communications between experimental and computational scientists are not as effective as they could be.

• Because the market for engineering or specialty polymers is limited, it is difficult to motivate industry to pursue the technologies the Air Force needs.

Structural polymers have been a focus of Air Force R&D since the early days of advanced composite development. However, the development of structural polymers has been deemphasized by the AFRL and many other government programs that have historically provided support, apparently because of the misconception that the industry is mature and that current capabilities will continue to support Air Force needs in the foreseeable future.

James McGrath (Virginia Polytechnic Institute and State University) introduced the subject of structural materials by reviewing recent advances in structural polymers including: (1) durability (including PES-toughened epoxy), (2) thermal stability (including NASA PETI-5 developments), (3) fire resistance, (4) nanocomposites (including polymer-metal and polymer-silica systems), (5) optically transparent films, (6) microporous glasses, (7) processing of vinyl ester systems (including sizing systems and shrinkage stresses), and (8) phenolic-based networks. He touched on many key areas of interest, including vinyl esters, void-free phenolics, phenyl ethynl matrix materials, phosphorus-containing polymers, and phthalonitrile-based thermosets.

Workshop participants identified the following research opportunities for structural polymers:

• functionalization of structural polymers (e.g., high refractive index)

• evaluation of durability in service environments (e.g., life prediction methods, optimization of available codes)

• the establishment of optimum balance of thermosets/thermoplastics

• the development of processing methods for space applications (e.g, rigidizing in place)

• the development of methods and metrics for evaluating combined environmental (light loads and radiation) effects, especially for space applications

• the identification of the industrial base for specialty polymers

The following materials and processing approaches were identified as promising areas for future R&D:

• barrier materials (e.g., for polymer-based cryotanks)

• metal salts to control coefficient of thermal expansion

• reactive oligomers (e.g., PETI-5)

• nonimide, high-temperature polymers

• structural control of block copolymers

• low-temperature curing systems

• ablative polymers

• organic-inorganic hybrids

• new reactive groups (e.g., perfluorocyclobutane)

• textile membrane systems (e.g., siloxane material)

• multimechanism curing approach

• crosslinkable thermoplastics

• photopolymerization processes (e.g., determine levels of glass transition temperature [Tg] that can be achieved)

• reinforcement technologies (e.g., new structural fibers)

• triphenyl phosphine oxide-based materials (high Tg's [>425°C], high moisture and thermal stability, high char yields)