The present invention provides novel heat stable polyamide-imide polymers having excellent flow properties and moisture stability which render them more readily processible into fibers, films, sheets and other molded articles. The polymers are prepared by forming the polycondensation product of one or more aromatic diamines, one or more tetrafunctional aromatic dianhydrides, and a difunctional aromatic carboxylic acid or amide-forming derivative thereof containing the groups ##STR1## linking two aromatic moieties, wherein R is CF.sub.3 or phenyl. In addition to improved flow properties, the polyamide-imide polymers of this invention also exhibit improved solubility properties in most organic solvents, improved resistance to attack by chlorinated solvents such as trichloroethylene as compared with polyimides, improved hydrophobic properties as well as excellent thermal properties, including resistance to thermooxidative degradation.