Synthesis and Characterization of Highly Soluble Polyamide-Imides Derived from α,α′-Bis[3,5-Dimethyl-4-(4-Trimellitimidophenoxy)-Phenyl]-1,4-Diisopropylbenzene

Abstract

A new diimide-dicarboxylic acid, α,α′-bis[3,5-dimethyl-4-(4-trimellitimidophenoxy)phenyl]-1,4-diisopropylbenzene (BDTPD), was synthesized by the condensation reaction of α,α′-bis[3,5-dimethyl-4-(4-aminophenoxy)phenyl]-1,4-diisopropylbenzene (BDAPD) with trimellitic anhydride in refluxing glacial acetic acid. A series of new polyamide-imide (PAIs) were prepared by direct polycondensation of BDAPD and various aromatic diamines in N-methyl-2-pyrrolidinone (NMP) using triphenyl phosphite and pyridine as condensing 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 diffractograms revealed that the polymers were amorphous. All the PAIs exhibited excellent solubility and could be readily dissolved in various solvents such as NMP, N,N-dimethylacetamide (DMAc), N,N-dimethylformamide, dimethyl sulfoxide, pyridine, cyclohexanone, tetrahydrofuran and chloroform at room temperature or upon heating at 70°C. Such PAIs had better solubility than those containing a hexafluoroisopropylidene linkage in the repeating unit of a PAI backbone. These PAIs had glass transition temperatures between 252 and 269°C and 10% weight loss temperatures in the range of 453–482°C and 462–485°C 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.