Synthesis and characterization of new functional poly(urethane-imide) crosslinked networks

To synthesize new functional poly(urethaneimide) crosslinked networks, soluble polyimide from 2,2′-bis(3,4-dicarboxyphenyl) hexafluoropropane dianhydride, 4,4′-oxydianiline, and maleic anhydride and polyurethane prepolymer from polycaprolactone diol, tolylene 2,4-diisocyanate and hydroxyl ethyl acrylate were prepared. Poly-(urethane-imide) thin films were finally prepared by the reaction between maleimide end-capped soluble polyimide (PI) and acrylate end-capped polyurethane (PU). The effect of polyurethane content on dielectric constant, residual stress, morphology, thermal property, and mechanical property was studied by FTIR, prism coupler, Thin Film Stress Analyzer (TFSA), XRD, TGA, DMTA, and Nano-indentation. Dielectric constant of poly(urethane-imide) thin films (2.39-2.45) was lower than that of pure polyimide (2.46). Especially, poly(urethane-imide) thin films with 50% of PU showed lower dielectric constant than other poly(urethane imide) thin films did. Lower residual stress and slope in cooling curve were achieved in higher PU content. Compared to typical polyurethane, poly(urethane-imide) thin films exhibited better thermal stability due to the presence of the imide groups. The glass transition temperature, modulus, and hardness decreased with increase in the flexible PU content even though elongation and thermal expansion coefficient increased. Finally, poly(urethane-imide) thin films with low residual stress and dielectric constant, which are strongly affected by the morphological structure, chain mobility, and modulus, can be suggested to apply for electronic devices by variation of PU.