Abstract: The present invention provides for a novel heat stable class of polyamide-imide polymers having excellent flow properties and hydrolytic stability which are prepared by forming the polycondensation product of one or more aromatic or aliphatic diamines, one or more additional comonomers selected from the group consisting of a tetrafunctional aromatic dianhydride, an aromatic or aliphatic dicarboxylic acid (or acid derivative thereof) and mixtures thereof, and a comonomer comprising a tri- or hexafluoro-substituted tricarboxylic acid anhydride (or acid derivative thereof) having the structure: ##STR1## wherein Z is CF.sub.3 or a phenyl radical.