On the kinetics of polymer degradation in solution

Abstract

Poly(2,2,2-trichloroethyl methacrylate), PTCMA, was irradiated in dilute dichloromethane solution with 16 MeV electron pulses of^{6 0}Co γ-rays. Both in the presence and absence of O₂, G(S)=9–10 was found at [PTCMA]<9 g/dm³. Indirect and direct radiation effects contributed to main-chain scission at a ratio of 7∶3. In contrast to earlier findings with dioxane solutions, at concentrations of up to 20 g/dm³ indications of crosslinking were not obtained. With CH₂Cl₂ solutions two modes of light scattering intensity (LSI) decrease were detected indicating the existence of two different macroradicals, one generated by the direct and the other by the indirect action of radiation. These radicals decayed with rate constants of 1.0·10³ s⁻¹ and 1.4·10¹ s⁻¹ and also reacted with C₂H₅SH with rate constants of 8·10⁴M⁻¹·s⁻¹ and 1·10³M⁻¹·s⁻¹, respectively. In O₂-saturated solutions both radicals formed peroxyl radicals, PO₂, wich combined generating products whose decomposition involved main-chain scission. The combination of PO₂-radicals was rate-determining in the consecutive series of reactions as inferred from the 2nd order decrease of the LSI.