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Abstract

Semi-cycloaliphatic (semi-alicyclic) polybenzoxazoles (PBOs) were investigated as candidates for flexible plastic substrates for liquid crystal displays (LCDs). PBOs were prepared by the one-pot polycondensation in polyphosphoric acid (PPA) from 2,2-bis(3-amino-4-hydroxyphenyl) hexafluoropropane (BAHP6F) with 1,3- and/or 1,4-cyclohexanedicarboxylic acid (CHDCA). The BAHP6F-based PBOs were soluble in various common organic solvents. In addition, the PBO films showed a relatively a high T _g exceeding 250^° C, excellent transparency, and a relatively low value of water absorption (< 0.5%), simultaneously. The BAHP6F-based PBO films were flexible, but the elongation at break (E _b ) in the stretching test did not exceed 20%. On the other hand, an ether-containing bis(o-aminophenol), 3,3^' -diamino-4,4^' -dihydroxydiphenylether (ADPE) exhibited much higher polymerization reactivity with CHDCA than BAHP6F, and as a result led to higher molecular weight PBOs. The ADPE-derived PBO films were relatively tough and showed a very high E _b , which exceeded 50%. However, the values of T _g were lower than those of the BAHP6F-derived PBOs, owing to the presence of the flexible ether linkages in the structure. Copolymerization using BAHP6F and ADPE led to excellent combined properties, namely, high T _g , high transparency, a high degree of toughness, and high solution-processability (solubility). The influence of the PBO preparation routes (one-pot technique or two-step method via thermal cyclization of PBO precursors) on the film transparency and other properties are also discussed. Some of the semi-cycloaliphatic PBOs examined in this work practically attained the target properties required for flexible substrates in LCDs..

Keywords

Soluble and transparent polybenzoxazoles high toughness low water absorption low dielectric constant flexible substrates for liquid crystal display

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Highly Tough and Highly Transparent Soluble Polybenzoxazoles

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