A self-polymerizable AB-type monomer for Diels-Alder (D-A) polymerization was prepared, and its polymerization was carried out in the melt phase and at high pressure in solution. The former method generated only low-molecular-weight polymer, but the latter one offered an efficient polymerization with increased molecular weight, due to the effect of high pressure on reactions with a negative activation volume. A pyridinium p-toluenesulfonate-catalyzed dehydration reaction of the D-A polymer led to a novel aromatic ladder polymer, poly(iptycene), which is soluble in common organic solvents and stable up to 350 degrees C. The NMR and UV-vis spectra of these polymers match the spectra of their corresponding model compounds, the synthesis of which is also reported.