Preparation and properties of new ortho-linked polyamide-imides bearing ether, sulfur, and trifluoromethyl linkages

A CF3-containing diamine, 2,2'-thiobis-[4-methyl(2-trifluoromethyl)4-aminophenoxy) phenyl ether] (DA), was successfully synthesized from 2-2'-sulfide-bis-(4-methyl phenol) and 2-chloro-5-nitrobenzotrifluoride. The sulfur containing diimide-diacid (DIDA) was prepared by condensation reaction of diamine DA and trimellitic anhydride. A series of novel organic-soluble polyamide-imides (PAIs) bearing flexible ether and sulfide links, electron-withdrawing trifluoromethyl groups and ortho-phenylene units were synthesized from DIDA, by direct polycondensation with various aromatic diamines in N-methyl-2-pyrrolidone using triphenyl phosphite and pyridine as a condensing agent in the presence of dehydrating agent (LiCl). The polyamide-imides were obtained in high yields and possessed inherent viscosities in the range of 0.42-0.95 dL g(-1). All of the polymers were amorphous in nature, showed outstanding solubility and could be easily dissolved in amide-type ;polar aprotic solvents (e.g., N-methyl-2-pyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide) and even dissolved in less polar solvents (e.g., pyridine and tetrahydrofuran). They showed good thermal stability with glass transition temperatures between 195-245 degrees C, 10% weight loss temperatures in excess of 485 degrees C, and char yields more than 50% at 700 degrees C in nitrogen atmosphere. Moreover, these PAN possessed low refractive indexes (n = 1.57-1.59) and low birefringence (Delta approximate to 0.02) due to the trifluoromethyl pendent groups and thioether bridged ortho-catenated aromatic rings that interrupt chain packing and increase free volume. (C) 2009 Elsevier Ltd. All rights reserved.