Thermal degradation of para-substituted polystyrenes

The thermal degradation of a series of para-substituted polystyrenes with e lectron-donating (CH3, NH2) and electron-attracting (NO2,CI,Br) substituent s has been studied in isothermal conditions at 600 degreesC using pyrolysis chromatography/mass spectrometry and in dynamic conditions using thermogra vimetry. The pyrolysis of these substituted polystyrenes gives monomer as t he main product for all polymers (60-80 wt.%). The other distribution of pr oducts supports the view that thermodestruction of these polymers starts fr om a random chain scission. The main process for all substituted polystyren es is depolymerization, similar to unsubstituted polystyrene. In the case o f para-substituted polystyrenes a good linear dependence was found between T-max on the thermogravimetry curve and the Hammett constants of the substi tuents (T-max =403.5-67.486 sigma (x)). The results indicate that the Hamme tt relationship can describe quantitatively the trends in T-max and thus th ermostability of substituted polystyrenes and that thermostability of these polymers depends only on electronic nature of substituent and their possib ility to stabilise macroradicals forming on chain scission. (C) 2001 Elsevi er Science Ltd. All rights reserved.