Heat-resistant and transparent polyimides derived from alicyclic dianhydrides and phthalazinone-based diamine

Advanced flexible display materials have drastically sparked considerable interest for heat-resistant, low dielectric, and transparent polyimide (PI) materials. In light of this, our study aims to develop high-performance semi-aromatic PI films, followed by investigate the correlations between bridged-alkyl/heteroaromatic ring structures and their thermal, dielectric, optical, and mechanical properties. Such PI films, namely AP-PIs, were synthesized with a one-step high-temperature method between 4-[4-(4-aminophenoxy) phenyl]-2-(4-aminophenyl)-1(2H)-phthalazinone (DHPZDA) and various commercial alicyclic dianhydrides. The incorporation of rigid phthalazinone structures significantly enhanced thermal resistance and mechanical flexibility, while simultaneously reducing their dielectric constant (Dk), attributed to the large polymer internal free volume. Impressively, the prepared films exhibit exceptional glass transition temperature (Tg) as high as 419 degrees C (DMTA tan delta peak), low Dk as low as 2.71, and elongation at break (epsilon %) up to 50.4%. Furthermore, AP-PI films demonstrate reasonable solubility and optical transparency within the UV-visible region. The maximum optical transmittance at 550 nm (T550 nm) could reach 83.01%. These desirable properties position these materials as promising candidates for flexible substrate applications.