Preparation of copoly(amide-imide)s via direct polycondensation

Preparation of various kinds of copoly(amide-imide) was carried out via direct polycondensation of trimellitic anhydride (TMA) with the corresponding diamine mixture in the presence of an equimolar amount of thionyl chloride (TC) as a condensing agent followed by thermal imidization. The resulting copoly(amide-imide)s had inherent viscosities in the range of 41 to 68 mL g⁻¹ and glass transition temperatures of 215°C to 291°C. These copoly(amide-imide)s had relatively good thermomechanical properties. That is, the initial decomposition temperature (IDT) and tensile strength were 350–409°C and 104–121 MPa, respectively. The melt viscosities of the copoly(amide-imide)s measured at 345°C under a frequency of 10² rad s⁻¹ were in the range of 4.8 × 10² ∼ 4.5 ˜ 10³ Pa s depending on comonomers, which are somewhat lower than that commerciallized PAI with 5.6 × 10³ Pa s.