The objective of this project is to identify and develop novel chemistries to replace 4,4’-methylenedianiline (MDA) in polymerization of monomer reactants (PMR) polyimides with both petroleum-derived and renewable/bioderived monomers. These chemistries aim to achieve the following: (1) eliminate toxicity and carcinogenic aspects of the polyimide; (2) maintain thermal and mechanical properties of the composites; (3) simplify composite processing; and (4) reduce life-cycle costs while developing structure-property relationships of these novel polyimides.

This project will systematically explore amino oligomers with phenyl, furyl, and/or isosorbide repeat units. In particular, the team has identified numerous structures and chemical routes to prepare these diamines from lignin and non-food carbohydrate sources. To down-select the chemical structures, researchers will use quantitative structure-activity relationship (QSAR) models to predict the physical characteristics and toxicity of the MDA alternative. They will then use synthetic organic chemistry to prepare, purify, and verify the synthesis of promising MDA alternatives. They will assess the processing characteristics of these MDA alternatives through solubility and rheology tests. Neat resin will be prepared and the cure will be studied to determine imidization temperature, extent of imidization, postcure temperature, and extent of cure. Neat resin samples will be prepared and tested to ensure high thermo-oxidative stability (TOS), thermal, and mechanical properties. In vitro toxicity testing of high performing resins will be performed to ensure the alternative PMR resin selected has low toxicity. Successful alternative PMR resins will be scaled up to produce enough for composite testing. Small amounts of pre-preg on carbon and glass fiber will be prepared in the laboratory. The pre-preg will then be used to fabricate small composite samples to assess TOS, mechanical, and other thermal properties. The highest performing alternative PMR resins will be commercially pre-pregged with carbon fiber and supplied to the Air Force, Navy, and Army for fabrication of parts to demonstrate this alternative PMR resin for DoD applications. An economic analysis will be performed to ensure the MDA alternative and PMR resin alternative has reduced life-cycle costs.

If successful, this project will identify and develop an MDA alternative with reduced or no toxicity and a PMR resin that will enable similar or improved performance relative to PMR-15. This will reduce costs and health effects associated with the manufacture of PMR-15 composites for Department of Defense (DoD) and other commercial applications. It will enable reduction or elimination of 7000 lbs/yr of hazardous materials and would help the Army meet the Environmental Protection Agency composite manufacturing National Emission Standard for Hazardous Air Pollutants (NESHAP) and Army environmental regulations. More importantly, there are many composites used in DoD, such as parts for rockets and structural parts near turbine engines, that currently use poor performing or expensive technology solutions because PMR-15 cannot be used due to its toxicity. A non-toxic PMR resin with properties comparable to that of PMR-15 will allow for greater use of PMR technology in DoD, will improve the performance of DoD weapons platforms, and will reduce the cost to maintain these platforms. Furthermore, the solutions will likely be bio-based, thus reducing dependence on petroleum resources and minimizing supply chain vulnerability associated with petroleum products. (Anticipated Project Completion - 2018)