Synthesis and optical properties of semi-fluorinated poly(ether imide)s derived from non-fluorinated 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) and trifluoromethyl-substituted diamines

A series of optically transparent and colorless semi-fluorinated poly(ether imide)s (PEIs) (III) were prepared from non-fluorinated 1,4-bis(3,4-dicarboxyphenoxy)benzene dianhydride (HQDPA) with various trifluoromethyl-substituted diamines. The III series showed more colorless and higher optical transparency with a cutoff absorption wavelength (λ0) below 370 nm than the IV series based on the corresponding non-fluorinated analogues and V series derived from CF3-free pyromellitic dianhydride (PMDA). Compared with the fluorinated VI series based on fluorinated 4,4′-hexafluoroisopropylidenediphthalic anhydride (6FDA), the semi-fluorinated III series not only exhibited much better optical transparency, but also had better mechanical and thermal properties. The III series had a tensile strength of 79.8–109.5 MPa, modulus of elasticity of 3.0–7.7 GPa and elongation at break of 14.2–26.7%, together with glass-transition temperatures (Tg) ranging from 214.3 to 265.1 °C and temperatures of 5% weight loss (T5%) beyond 530 °C. Meanwhile, the novel semi-fluorinated PEI IIIb was optically transparent and colorless with a λ0 of 367 nm coupled with dielectric constants below 3.2 and contact angles against water over 112°. In particular, the optically transparent IIIa exhibited the best tensile strength of 109.5 MPa when compared with already reported counterparts.