Thermal degradation study of phenolphthalein polycarbonate

Abstract

AbstractPhenolphthalein polycarbonate underwent complicated thermal degradation which included random scission, rearrangement, hydrolysis, Friedel‐Crafts acylation, and cross‐linking. The carbonate group and lactone ring were both susceptible to thermal deterioration. Kinetic parameters were determined from the dynamic TGA thermograms. During early stages of degradation the measured reaction order was nearly 1, which suggested a random chain scission mechanism. The measured activation energy was 42.6 kcal/mol, compared with 41.2 kcal/mol calculated from isothermal aging. The Arrhenius preexponential constant was 3.09 × 1011 min−1. Below 80% weight residue the plot of fractional weight against 1/T revealed that complicated reactions with different activation energies occurred simultaneously and resulted in a final overlap of TGA curves for different heating rates indicative of cross‐linking and a lower preexponential constant. The reaction order changed and kept increasing in the last stages of degradation. Pyrolysis of this polymer was performed at 350°C under vacuum, followed by GC‐mass spectroscopic identification of products. The volatile products (17.5%) contained CO2, CO, O2, H2O, phenol, fluorenone, diphenyl carbonate, xanthone, anthraquinone, 2‐hydroxylanthraquinone, 2‐benzoxyanthraquinone, phenolphthalein, and trace amounts of benzoxyphenol and hydroquinone; the other 82.5% of products was insoluble gel. Functional group changes were examined by Fourier transform infrared spectroscopy (FT‐IR). Lactone, carbonate, and aromatic absorptions decreased during degradation. Increasing absorptions at 1739, 1728, 1280–1200, and 1138–1075 cm−1 were believed to result from aromatic ester (1728 cm−1) and phenyl aromatic ester (1739 cm−1) cross‐linkages ortho to the aromatic ether group (increases at 1155 cm−1 and 1280–1200 cm−1). Existence of 2‐hydroxyanthraquinone and xanthone contained in the crosslinked polymer matrix were also detected. Mechanisms for random scission, rearrangement, Friedel‐Crafts acylation, hydrolysis, and cross‐linking were suggested.