ABSTRACT
Abstract Aromatic polyimides have been widely used in microelectronics, aerospace and other industries. However, many commercially available polyimides have restricted applications due to their insolubility, intractability and processing requirements; therefore, many efforts have been made in synthesizing soluble, tractable polyimides without appreciable sacrifice in their desired properties. One of the successful approaches has been to introduce pendant phenyl and alkyl groups into the polymer. Bismaleimides are another approach to improve processibility. Hence, in the present study, new diamine monomers were synthesized by treating a substituted aldehyde with 2,6-dimethyl aniline in the presence of dry hydrochloric acid to yield the diamine bis(4-amino-3,5-dimethyl phenyl) X′ phenyl methane (where X′ = Cl, Br, F, –OCH2C6H5, –OCH3) and bis(4-amino-3,5-dimethyl phenyl) anthramethane. A series of organosoluble polyimides were prepared from the diamine with various aromatic tetra carboxylic acid dianhydrides via one-step and two-step methods. All the polyimides were soluble in aprotic solvents such as NMP, DMF, DMAc and DMSO. The polyimides show excellent thermal stability and good mechanical properties. The glass transition temperature of the various polyimides ranges from 210 to 325◦C and the temperatures at which 10% weight loss occurs are in the range 460-496◦C. All polyimides formed tough transparent films with tensile strength 79-118 MPa, % elongation 8-12% and modulus 1.5-2.3 GPa. These polyimide films have low dielectric constant (3.29-3.80 at 1 kHz and 3.14-3.76 at 10 kHz) and low moisture uptake 0.52-1.10%. Bismaleimides were also synthesized from the prepared diamines and maleic anhydride via bismaleamic acid as an intermediate followed by cyclodehydration. The structure was confirmed by FT-IR, 1H-NMR and elemental analyses. Further, a series of polyaspartimides were synthesized by addition reaction of bismaleimides (BMDA) with various diamines. The polymers were characterized by IR and elemental analysis. The Tg of polyaspartimides is in the range of 125-278◦C and T 10% weight loss is in the range of 398-476◦C.
