Differential thermogravimetric curves for a mixture of evaporable and degradable chain oligomers

Abstract

Since the boiling point of oligomers increases with increasing chain length, differential thermogravimetric (DTG) curves of polymerization products are uniquely related to the molecular mass distribution of the oligomers in the chain length region in which the degradation rate is less than the rate of evaporation. Degradation is manifested by narrow, chain length-invariant peaks of the DTG curves so that they are distinguishable from broad DTG bands due to the evaporation of the mixture of oligomers. The detachment of the terminal groups at a temperature T ₁ and main chain scission at T _d > T ₁ are accompanied by dimerization of macroradicals, evaporation of the dimers in the T ₁ < T < T _d interval, and appearance of the full degradation peak at T ≈ T _d . The pattern of DTG curves based on these concepts has been calculated on the assumption of free convection in the boundary layer and a spatially uniform degradation in the melt. As an example, DTG curves for the products of tetrafluoroethylene polymerization in liquid solutions have been considered.