Thermal degradation of para-substituted polystyrenes

Abstract

The thermal degradation of a series of para-substituted polystyrenes with electron-donating (CH 3, NH 2) and electron-attracting (NO 2,Cl,Br) substituents has been studied in isothermal conditions at 600°C using pyrolysis chromatography/mass spectrometry and in dynamic conditions using thermogravimetry. The pyrolysis of these substituted polystyrenes gives monomer as the main product for all polymers (60–80 wt.%). The other distribution of products supports the view that thermodestruction of these polymers starts from a random chain scission. The main process for all substituted polystyrenes is depolymerization, similar to unsubstituted polystyrene. In the case of para-substituted polystyrenes a good linear dependence was found between T max on the thermogravimetry curve and the Hammett constants of the substituents ( T max =403.5–67.486 σ x ). The results indicate that the Hammett relationship can describe quantitatively the trends in T max and thus thermostability of substituted polystyrenes and that thermostability of these polymers depends only on electronic nature of substituent and their possibility to stabilise macroradicals forming on chain scission.