Fast and eco-friendly synthesis of novel soluble thermally stable poly(amide-imide)s modified with siloxane linkage with reduced dielectric constant under microwave irradiation in TBAB, TBPB and MeBuImCl via isocyanate method

Abstract

A new series of poly(amide-imide)s (PAI) modified with a siloxane linkage was synthesized under microwave radiation in ionic liquids and organic salts via the isocyanate method. The polymerization reactions of a novel siloxanic diacid monomer with 4,4'-methylene-bis(4-phenylisocyanate) MDI were studied in ammonium, phosphonium, and imidazolium-type organic salts. These poly(amide-imide-siloxane)s (PAI-Si)s were obtained with high yields and good inherent viscosities ranging from 0.30 to 0.55 dL/g. The normally high softening temperatures and poor solubility of PAIs in organic solvents were improved via the incorporation of the flexible siloxane segments into the polymer backbone. The PAI-Sis showed glass transition temperatures around 100°C and their 10% mass loss was about 300°C. They have a char yield in the range of 30-40% at 800°C. Calculated limiting oxygen index values of the polymers were about 30; therefore, they can be considered as self-extinguishing. The dielectric constants of these silane-containing PAIs (2.5) are lower than common siloxane-free polyimides (∼ 3). Their good thermal stability, enhanced solubility, and low dielectric constants suggest they may function as electrical insulators. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 Copyright © 2012 Wiley Periodicals, Inc.