Thermal oxidation of polybutadiene. Part 2: Mechanistic and kinetic schemes for additive-free non-crosslinked polybutadiene

The thermal oxidation of an additive-free, uncrosslinked, hydroxy-terminated polybutadiene has been studied at temperatures ranging from 60 to 120 °C and oxygen pressures from 0.01 to 3.1 MPa by gravimetry, IR spectrophotometry and chemical titration of epoxides and hydroperoxides for samples of 20 and 265 μm thicknesses. A mechanistic scheme with 17 elementary steps among which radical additions to double bonds, decomposition of the resulting alkyl radicals and the corresponding terminations was proposed on the basis of qualitative observations and literature data. A kinetic scheme, composed of 8 differential equations for the 8 reactive species plus 4 equations for the measured quantities, has been derived from the mechanistic scheme. The kinetic parameters, essentially elementary rate constants, have been determined using an inverse approach. A set of physically reasonable parameter values has been obtained. With these parameters, the kinetic model is able to generate kinetic curves of the mass gain, carbonyl build-up, hydroxyl build-up, double bond consumption, epoxide build-up and hydroperoxide build-up, reasonably close to experimental ones, in the full domain of temperatures, oxygen pressures and sample thickness under consideration.