Effect of functional groups on the ­thermal degradation of copolymers

Thermal degradation mechanisms of the copolymers of styrene (St) with methacrylonitrile (MAN) and α-methylstyrene (αMSt) were studied by pyrolysis gas chromatography (Py-GC) and thermogravimetry (TG). Thermal degradation of vinyl polymers in flash pyrolysis proceeded mainly in the competition between depolymerization and back biting reaction caused by abstraction of H atom at α-position in pen-penultimate unit. Monomer molecules were regenerated by depolymerization, and dimer, trimer and ologomers were produced by back biting reaction. Methyl groups at α-position of monomer unit strictly hindered the back biting reaction. The role of functional groups on the thermal degradation was elucidated on the basis of bond dissociation energies­of main chain (QCC), apparent activation energies­(ΔEa) obtained by Ozawa's method from the TG­curves at various heating rates. Effect of chemical reactivity of C≡N group in MAN unit on the thermal degradation was clarified by the controlled rate thermogravimetry (CRTG). Copyright © 2002 John Wiley & Sons, Ltd.