Preparation and performance testing of novel bendable optically transparent fluorinated hyperbranched linear long chain segment poly(amide-imide) films

Abstract

In the present work, we prepared a fluorinated triacid monomer from a triamino monomer (TFAPOB) and trimellitic anhydride using the thermal snap ring method. Subsequently, a series of fluorinated hyperbranched linear long chain segment poly(amide-imide)s (PAIs) were prepared by reacting this triacid monomer with four linear diamine monomers, respectively, which contained pendant units. The degree of branching of each of the four polymers was calculated using ¹H nuclear magnetic resonance (NMR) spectroscopy (51%–54%). The prepared polymers exhibited good solubility and film-forming properties in common organic solvents and were thermally stable (T_10%: 562–602 °C, T_gs: 228–237 °C). Subsequently, the mechanical and photovoltaic properties of the polymers were investigated. The tensile strength of the films was in the range of 85.5–100.7 MPa, the elongation at break was in the range of 7.0–8.2%, and the transparent PAI films had low dielectric constants (2.10–2.48). In terms of optical properties, the birefringence values of the PAI films were in the range of 0.0010–0.0018 (650 nm), and the refractive index could be adjusted by means of copolymerization. The prepared PAI films have good transmittance (450 nm: 86%–88%; 550 nm: 89%–91%; 800 nm: 91%–93%), cut-off wavelengths in the range of 332–353 nm, and a small absorption range in the near infrared region (1300 and 1560 nm). In addition, the PAI films are very light in color, especially the PAI-3 films (CIE 1931 X: 0.34806; Y: 0.33371; yellowness (YI): −6.33; whiteness (H): 90.63, whiteness (R): 88.47), which have chromaticity parameters that are similar to those of commercially available transparent films such as polymethyl methacrylate (PMMA) and poly(ethylene terephthalate) (PET), and which are also characterized by a high degree of thermal stability.