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 (lambda(0)) 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 (T-g) ranging from 214.3 to 265.1 degrees C and temperatures of 5% weight loss (T5%) beyond 530 degrees C. Meanwhile, the novel semi-fluorinated PEI IIIb was optically transparent and colorless with a lambda(0) of 367 nm coupled with dielectric constants below 3.2 and contact angles against water over 112 degrees. In particular, the optically transparent IIIa exhibited the best tensile strength of 109.5 MPa when compared with already reported counterparts.