ABSTRACT
Abstract Polyimides and poly(amide-imide)s are of high interest for many engineering applications due to their excellent thermal and mechanical properties. The aerospace, automotive, and microelectronics industries have developed many important applications. However, the processing of these thermoplastic polymers has been greatly hindered because they lack softening or melting behaviour at usual processing temperatures, and they tend to degrade before or at the softening temperature. Various attempts have been made to bring down the Tg or melting temperature of aromatic polyamides to make them processable, either by introducing kinked or flexible bridging units. Unfortunately, the loss of thermal stability and significant decrease in mechanical properties on heating are usually a consequence of the reduced chain stiffness. In the present study, a series of novel aromatic diamines bis(4-amino-3,5-dimethyl phenyl) (X) phenyl methane (X→3chloro, 3-bromo, 4-methoxy) from corresponding aldehydes and 2,6-dimethyl aniline; and bis(4-amino3,5-dimethyl phenyl) cyclohexane from cyclohexanone and 2,6-dimethyl aniline; bis(4-amino-3,5-dimethyl phenyl) cycloheptanone from cycloheptanone and 2,6 dimethyl aniline; and bis(p-amino phenoxy)-methyl phenyl silane from p-aminophenol and dichloro methyl phenyl silane were prepared. Tetrimide dicarboxylic acids were prepared by reacting the prepared diamines with PMDA/BPDA and p-aminobenzoic acid. The polymers were prepared by treating the tetrimide diacid with different aromatic diamines. The structures of the monomers and polymers were identified by elemental analysis, FT-IR, 1H-NMR and 13C-NMR. The polymers show excellent solubility. The polymers are amorphous and have high optical transparency. They also show good thermal stability and their Tg is found to be in the range 268-372◦C. They had 10% weight losses at temperatures beyond 530◦C and left more than 50% char yield even at 800◦C in nitrogen atmosphere. The thin films cast from DMAc exhibit tensile strengths of 96-101 MPa, elongations at break of 9-14% and initial moduli of 1.9-2.3 GPa. The properties of the different polymers were compared and discussed and correlated to their structures.
