Abstract
High performance engineering thermoplastics exhibit excellent thermomechanical performance and chemical resistance, however, the rigid polymeric main chains that are derived from highly or fully aromatic repeating units impose processing challenges. The design of photo-reactive precursors now enables additive manufacturing of poly(amide imide) (PAI) precursor organo-gels via UV-assisted direct ink write (DIW) printing. Solution rheology revealed prerequisite high solution viscosities and shear thinning behavior of organic solutions of the PAI precursors. Additionally, photorheology of PAI precursors exhibited rapid gelation and high gel strengths, enabling production of self-supporting organo-gels that are necessary for successful DIW. Thermal post-treatment of the printed organo-gels revealed isotropic linear shrinkage as low as 26% during drying and imidization. The reduced chain rigidity of the poly(amide imide), relative to fully-aromatic polyimides, prevented quantitative thermal removal of the poly (hydroxyethyl acrylate) (poly(HEA)) scaffold, resulting in a decreased glass transition temperature (263 °C) relative to commercial PAI (290 °C). Moreover, crosslinking of the PHEA during thermal imidization limited scaffold removal upon solvent extraction, however, suggested the formation of novel multiphase polymers. Selective dissolution of the PAI from the crosslinked PHEA enabled assessment of the role of the scaffold on thermomechanical properties and characterization of printed PAI. Spectroscopic and thermal analysis confirmed the formation of the desired PAI composition with this photochemical synthetic method.
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