Viscosity effects on the thermal decomposition of bis(perfluoro-2-N-propoxypropionyl) peroxide in dense carbon dioxide and fluorinated solvents

The thermal decomposition of the free-radical initiator bis(perfluoro-2-N-p ropoxyprionyl) peroxide (BPPP) was studied in dense carbon dioxide and a se ries of fluorinated solvents. For the fluorinated. solvents, the observed f irst-order decomposition rate constants, k(obs) increased with decreasing s olvent viscosity, suggesting a single-bond decomposition mechanism. The k(o bs), values are comparatively larger in dense carbon dioxide and similar to the "zero-viscosity" rate constants extrapolated from the decomposition ki netics in the fluorinated solvents. The decomposition activation parameters demonstrate a compensation behavior of the activation enthalpy with the ac tivation entropy upon change in solvent viscosity. Comparison of the change in activation parameter values upon change in solvent viscosity for BPPP w ith two additional initiators, acetyl peroxide (AP) and trifluoroacetyl per oxide (TFAP), further suggests that carbon dioxide exerts a very minimal in fluence on the decomposition mechanism of these initiators through solvent- cage effects.