Synthesis of poly(benzylidene phthalide)s: A new class of polymers

Pyromellitic dianhydride (PMDA) was condensed with different aromatic diacetic acids via a Perkin reaction to produce new polymers containing the benzylidenephthalide group in the backbone. Yields ranged from 50 to 90% with inherent viscosities ranging from 0.07 to 0.37 dL/g. Polymerizations at 275°C for 4 h using p‐phenylenediacetic acid and PMDA gave the polymer with highest inherent viscosity. However, polymerization under identical conditions of p,p′‐diphenyl ether diacetic acid, each with PMDA, yielded poor results. For these two monomers the best polymerization conditions were 250°C for 8 h. In general, the most thermally stable polymer was derived from the diphenyl ether diacetic acid monomer (308°C). This polymer was obtained in highest yields and gave the greatest amount of pyrolytic residue in argon (67%).