Synthesis and characterization of highly soluble polyamide-imides derived from alpha,alpha '-bis[3,5-dimethyl-4-(4-trimellitimidophenoxy)-phenyl]-1,4-diisopropylbenzene

A new diimide-dicarboxylic acid, alpha,alpha'-bis[3,5-dimethyl-4-(4-trimell itimido- phenoxy)phenyl]-1,4-diisopropylbenzene (BDTPD), was synthesized by the condensation reaction of alpha,alpha'-bis[3,5-dimethyl-4-(4-aminopheno xy)phenyl]-1,4-diisopropylbenzene (BDAPD) with trimellitic anhydride in ref luxing glacial acetic acid. A series of new polyamide-imide (PAIs) were pre pared by direct polycondensation of BDAPD and various aromatic diamines in N-methyl-2-pyrrolidinone (NMP) using triphenyl phosphite and pyridine as co ndensing agents. The polymers were produced with high yield and moderate to high inherent viscosities of 0.77-1.03 dl g(-1). Wide-angle x-ray diffract ograms revealed that the polymers were amorphous. All the PAIs exhibited ex cellent solubility and could be readily dissolved in various solvents such as NMP,N,N-dimethylacetamide (DMAc), N,N-dimethylformamide, dimethyl sulfox ide, pyridine, cyclohexanone, tetrahydrofuran and chloroform at room temper ature or upon heating at 70 degreesC. Such PAIs had better solubility than those containing a hexafluoroisopropylidene linkage in the repeating unit o f a PAI backbone. These PAIs had glass transition temperatures between 252 and 269 degreesC and 10% weight loss temperatures in the range of 453-482 d egreesC and 462-485 degreesC in nitrogen and air atmospheres, respectively. The tough polymer films, obtained by solution casting from DMAc solution, had a tensile strength range of 80-103 MPa and a tensile modulus range of 1 .6-2.0 GPa.