Abstract: Biphenylene end-capped low molecular weight thermally stable aromatic polymers and the process for their preparation. The invention is further directed to crosslinked biphenylene end-capped aromatic polymers and to the process for their preparation. The process for preparing the biphenylene end-capped low molecular weight thermally stable aromatic polymers comprises carrying out a misbalanced polymerization reaction of a suitable aromatic aminoketone compound and a suitable aromatic ketomethylene compound and thereafter adding a monofunctional biphenylene compound.