The kinetics of polymer degradation in solution: Pt. 14

Poly(dimethyl itaconate) (PDMI), underwent main-chain scission upon irradiation with 60Co-γ-rays or 16 MeV electrons in dilute 1,4-dioxane or acetone solution; crosslinking was not detected. In dilute 1,4-dioxane solution, a pronounced indirect radiation effect was found with G(S)p (related to the energy absorbed directly by the polymer) decreasing gradually from 4.8 to 2.3 scissions/100 eV for cPDMI increasing from 0.038 to 0.38 base mol/1. Pulse radiolysis experiments in conjunction with time-resolved light scattering measurements indicated at least two different intermediates, the decay of which resulted in main-chain scission. On the basis of results from quenching experiments with N2O, the existence of a short-lived intermediate (τ << 50 μ sec), probably an electronically highly excited state resulting from the combination of electrons with positive ions, is suggested. Long-lived intermediates (τ ∼ 3 msec) are attributed to lateral macroradicals formed by bond cleavage in the side groups. The decomposition of these radicals via main-chain scission was suppressed by O2 and C2H5SH. (author)