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Polymer Science and Engineering: The Shifting Research Frontiers
stability in air at 240°C to permit blending and processing with conventional polymers. The oxidative and hydrolytic stability is significantly increased when the conducting polymer is used in the form of blends with conventional polymers. Clearly, research to improve the stability of conducting polymers is essential to commercial applications in the future.
Polyaniline is currently the leading conducting polymer used in technological applications and is commercially available in quantity. Polypyrrole and derivatives of polythiophene and poly(phenylene vinylene) also have significant potential technological applications. Rechargeable polyaniline batteries and high-capacity polypyrrole capacitors are in commercial production.
Ironically conducting polymers are now being used in batteries and electrochromic displays. However, even though conductivities of greater than 10-3 S/cm are now achievable with gel electrolytes, the goal of preparing single-ion (and specifically cation) conductors with comparable conductivities has remained elusive. Tight ion pairing between Li+ and polymer-bound anions (usually sulfonates) is responsible for the significantly lower conductivities. Also, new approaches for the synthesis of polymer electrolytes as thin films directly on electrodes (via, for example, photopolymerization) are needed to complement novel multilayer battery fabrication technology. Along these lines, a key goal is the design of multifunctional polymers capable of transporting only cations, stabilizing a battery system against overcharging, and exhibiting low reactivity at alkali metal and metal oxide electrodes. Perhaps most important, electrode-polymer electrolyte reactions need to be examined from a fundamental point of view because these represent a major problem for battery cyclability and overall stability.
The field of sensors is diverse, reflecting our need to control increasingly complex systems—including environments, processes, equipment, vehicles, and biomedical procedures—that are characterized by high levels of automation. The key to the success of such automated systems is the measurement technology, which demands rapid, reliable, quantitative measurement of the required control parameters. These parameters include temperature, pressure, humidity, radiation, electric charge or potential, light, shock and acoustic waves, and the concentrations of specific chemicals in any environment, to name just a few. Obviously, the types of sensors that are applied to such wide-ranging measurements are quite varied in type and principle of operation. Nevertheless, polymers play a significant role as enabling active materials for the design of sensors that are extending current limitations of sensitivity, selectivity, and response time.
A great deal of sensor research and development is focused on tailoring polymeric materials for applications in the chemical and biomedical fields. First, polymers can be functionalized through the incorporation, in their syntheses or