Phthalide as an activating group for the synthesis of poly(aryl ether phthalide)s by nucleophilic aromatic substitution

The phthalide ring was examined as an activating group for nucleophilic aromatic substitution. The proposed mechanism by which activation occurs is through a ring opening of the phthalide ring to form a Meisenheimer-like sigma complex. 3,3-Bis(4-fluorophenyl)phthalide was synthesized and examined under different reaction conditions to determine its suitability for polymer formation. Semiempirical calculations at the PM3 level suggested that 3,3-bis(4-fluorophenyl)phthalide is only moderately activated, whereas H-1, C-13, and F-19 NMR spectroscopy suggested that the monomer was not sufficiently activated for nucleophilic aromatic substitution. However, low-molecular-weight polymers (number-average molecular weight < 7000 g/mol) were produced from bisphenol A, hydroquinone, and phenolphthalein. The polymers were characterized by gel permeation chromatography, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry, NMR spectroscopy, and differential scanning calorimetry. The polymers displayed relatively high glass-transition temperatures. (C) 2002 Wiley Periodicals, Inc.