Refining and Designing Photoactive Polyimide Precursors for Additive Manufacturing

Creating 3D objects out of high performance polymers, such as polyimides, is notoriously difficult since the highly stable polymer backbone limits processibility without extreme conditions. However, designing the polyimide precursor to crosslink upon photoirradiation enables the additive manufacturing of polyimides into complex, 3D objects. Crosslinking the photoactive polyimide precursor forms a solid 3D organogel, then subsequent thermal treatment removes the sacrificial scaffold and simultaneously imidizes the precursor into a 3D polyimide. The collaborative efforts of the Long and Williams group at Virginia Tech created three chemically distinct photoactive polyimide precursors to additively manufacture 3D polyimide objects for aerospace applications and to maintain the nuclear stockpile. The first chapter of this dissertation introduces fully aromatic polyimides and the additive manufacturing techniques used to print photoactive polyimide precursors. The second chapter reviews the common pore forming methods typically utilized to develop porous polyimides for low dielectric applications. The following chapters investigate the impact of the sacrificial scaffold on the thermo-oxidative aging behavior of the polyimide precursors after imidization, then focuses on lowering the imidization temperature of the polyimide precursor using base catalysis. These investigations lead to the creation of photoactive polysalts with polyethylene glycol (PEG) side chains to develop 3D, porous polyimides with tunable morphologies. Varying the molecular weight and concentration of the PEG side chains along the backbone tuned the pore size, and the photoactive nature of the polyimide precursor enabled 3D, porous polyimides printed using digital light processing.