In this project funded by the Macromolecular, Supramolecular and Nanochemistry Program of the Chemistry Division, Eric Fossum of Wright State University will explore the application of meta-activation in nucleophilic aromatic substitution to polycondensation and the preparation of step-growth polymers with novel structures. The approach is to synthesize 1,3-difluoro-substituted aryl monomers with a variety of pendant electron withdrawing groups. The reactivity of these monomers towards nucleophilic aromatic substitution will be studied and promising systems will be translated into polymerization reactions. The resulting polymers would be meta-linked counterparts to several well known classes of polyarylenes. The thermal and mechanical properties of the polymers will be determined. The broader impacts involve training master's and undergraduate students and disseminating results in publications and seminars.
This work will enhance our fundamental understanding about how to synthesize new polymers (plastics) with high thermal stability and beneficial mechanical properties. The results of these studies could have many important long term impacts on applications in which engineering plastics are important, including automotive, packaging, and aerospace industries.
Scientific Merit The overall goal of this project was to develop efficient routes to functionalized poly(arylene ether)s, PAEs, derived from a series of activated 3,5-difluoro aromatic compounds. PAEs are a class of polymers known as engineering thermoplastics that possess excellent mechanical, thermal, and chemical resistance properties. These properties make PAEs the material of choice for a wide variety of applications ranging from the electronics industry to gas separation membranes. The introduction of new functionality to these systems allows the researcher to readily tailor the properties of the material to meet a specific need. The primary scientific outcome of this project was the development of new methodologies, based on a hitherto underutilized reaction, to prepare an entirely new set of polymeric materials. A series of activated 3,5-difluoro aromatic compounds was prepared and utilized as a unique route to prepare a variety of functional PAE materials. As can be seen in Scheme 1, a traditional PAE is prepared from a monomer in which the activating group is located in what is termed the para position, while the materials from this work are activated from the meta position. This subtle change in structure gives rise to stark differences in the resulting polymer structures and allows the introduction of a wide variety of functional groups without directly altering the backbone of the polymer. The activated 3,5-difluoro aromatic compounds utilized in this project are shown in Figure 1 and each of them was successfully converted into the corresponding PAE. Initial work has also been carried out to introduce functional groups, such as sulfonic acids for fuel cell proton exchange membranes with enhanced properties and iodo moieties that enable facile tailoring of properties, at the truly pendent positions of these systems. The methodology developed provides the scientific community a viable option to rapidly prepare a multitude of engineering thermoplastics with tailored chemical and physical properties. Broader Impacts In addition to the development of new and promising methodologies for the synthesis of functional engineering thermoplastics, the broader impacts resulting from this project included the scientific training of twenty students, six M.S. level and 14 undergraduates, which provided them with the necessary "skill set" to succeed in their chosen endeavors. The "skill-set" consisted of a variety of synthetic and analytical techniques, report writing, manuscript preparation, and presentation methods. Thirteen of the twenty students involved with the project were female, which served to broaden the participation of this underrepresented group in scientific endeavors. In addition, each summer we opened our laboratory for tours and the PI gave an introductory talk to a group of top-notch area high school students who participated in the Wright Scholars Program that is hosted at Wright Patterson Air Force Base. The laboratory tours involved brief descriptions of our ongoing projects by each of the students supported by the current NSF funds.
