Kinetic study of anhydride formation during thermal degradation of isotactic and atactic polymethacrylic acid

A kinetic study of anhydride formation in isotactic and atactic polymethacrylic acids (PMA) has been performed at about 200° using a vacuum thermobalance. The results obey first order kinetics and show that the rate of water loss is about four times higher for the isotactic PMA than for the atactic isomer. The activation energies are almost identical (42 ± 1 kcal per mole); it is concluded that the arrangement of neighbouring carboxyl groups is more favourable for the formation of a cyclic anhydride by intramolecular reaction in the case of the isotactic PMA.