the present invention provides novel heat stable polyamide - imide polymers having excellent flow properties 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 of more aromatic diamines , one or more trifunctional acid anhydride monomers , and one or more tetrafunctional aromatic dianhydrides , at least one of said monomers containing the groups ## str1 ## linking two aromatic moieties , wherein r is cf 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 .