High molecular weight aromatic polyformals containing phthalazinone moiety were simply synthesized with a high-intensity mixing methodology without the presence of phase-transfer catalyst. Aromatic polyformals can readily be afforded in a very short time and at temperatures ranging from 50 to 140 degreesC. These polyformals showed high glass-transition temperatures together with superior thermal properties when compared with a 4,4'-isopropylidenediphenol (BPA)-type polyformal and polycarbonate. The glass-transition temperatures of these aromatic polyformals ranged from 94 to 229 degreesC. The molecular weights of the polyformals were examined by gel permeation chromatographic technology, and the result showed that the cyclic formation during the condensation could be dramatically reduced at elevated temperature. The molecular weights and solubility increased with an increasing content of bisphenol A in the polyformals. The result demonstrated that the aromatic polyformal with 50% phthalazinone moiety showed the comparable thermal properties with commercial BPA polycarbonate. This method promisingly opened an effective approach to synthesize aromatic polyformals with high molecular weight and without cyclic formations.