Symmetric and asymmetric spiro-type colorless poly(ester imide)s with low coefficients of thermal expansion, high glass transition temperatures, and excellent solution-processability

Abstract

In this work, we present several new poly(ester imide)s (PEsIs) with low coefficients of thermal expansion (CTE), excellent optical transparency, very high heat resistance (Tg), film ductility, and solution-processability. Symmetric and asymmetric spiro-type tetracarboxylic dianhydrides containing ester linkages (TA-s-Spiro and TA-a-Spiro) and diamines (AB-s-Spiro and AB-a-Spiro) were synthesized using xanthene-based isomeric bisphenols with a fluorenyl side group. The chemically imidized PEsIs were highly soluble in various common solvents including less polar non-amide solvents, and yielded stable solutions with high solid contents. The properties of the spiro-type PEsIs were systematically investigated and compared with those of the cardo-type counterparts. A PEsI derived from 1,2,3,4-cyclobutanetetracarboxylic dianhydride (CBDA), AB-a-Spiro, and 2,2′-bis(trifluoromethyl)benzidine (TFMB) achieved outstanding combined properties, i.e., a very low CTE (10.5 ppm K−1), excellent optical transparency (YI = 3.4, T400 = 80.8%), a very high Tg (351 °C) and solution-processability. Thus, the PEsIs are promising candidates as novel plastic substrates for use in image display devices. The isomer effects on the properties were also investigated and a possible mechanism for these effects is proposed.