Thermal oxidation of polybutadiene. Part 3: Molar mass changes of additive-free non-crosslinked polybutadiene

This work deals with the thermal oxidation of an additive free, non-crosslinked, hydroxy-terminated polybutadiene of predominantly trans 1-4 structure. The first part was devoted to the description of the polymer behaviour in a wide range of temperature, oxygen pressure and thickness. The second part used these experimental data plus some additional data obtained from chemical titrations (hydroperoxides' and epoxides' concentrations) to build a mechanistic scheme describing the structural changes at the molecular scale (monomer unit) for one temperature: 100 °C. In this third part, we attempted to study the structural changes at the macromolecular scale from rheometric measurements. Polybutadiene essentially undergoes crosslinking resulting from radical additions to double bonds. However, the kinetic analysis suggests that intermolecular additions are largely less frequent than intramolecular ones (leading for instance, to cyclohexene rings in the case of alkyl radicals or to cyclic peroxides in the case of peroxy radicals). The relative contributions of intra- and intermolecular additions are estimated from the kinetic model elaborated in the second part of this article, using an inverse approach.