High solubility and optical transparency of novel polyimides containing 3,3′,5,5′-tetramethyl pendant groups and 4-tert-butyltoluene moiety

A series of novel polyimides (3a-d) were prepared from 3,3′,5,5′-tetramethyl-4,4′-diaminodiphenyl-4”-tert-butyltoluene (1) with four aromatic dianhydrides via a one-step high-temperature polycondensation procedure. The obtained polyimides showed excellent solubility, with the dissolvability at a concentration of 10 wt% in most amide polar solvents and chlorinated solvents. Their films were nearly colorless and exhibited high optical transparency, with the UV cutoff wavelength in the range of 322-350 nm and the wavelength of 80% transparency in the range of 395-414 nm. They also showed low dielectric constant (2.72-2.91 at 1 MHz) and low water absorptions (0.37-0.62%). Moreover, these polyimides possessed high glass transition temperatures (Tg) (above 321 °C) and good thermal stability with 10% weight loss temperatures in the range of 526-547 °C in nitrogen atmosphere. In comparison with the analogous polyimides non-containing 3,3′,5,5′ -tetramethyl pendant groups, the resultant polyimides 3a-d showed better solubility, higher optical transparency and lower dielectric constant.