Compensation effect: sublimation, diffusion in polymers, polymer degradation

Thermogravimetrically obtained temperature dependences of kinetics of degradation (in nitrogen and oxygen) of a series of crosslinked polyurethane acrylates, kinetics of solvent diffusion through the same crosslinked urethane acrylates, and kinetics of sublimation of a series of azepine derivatives were re-evaluated. Arrhenius equation parameters for these series of processes were deduced. In all cases, a linear dependence of activation energies, E-a, and pre-exponential factors, A(0), (compensation effect) was observed. Sublimation of azepines occurred with isoconversion temperature of approximate to 333 K and lnA(0) = 0.19E(a) + 7.48, with regression coefficient, R-2 = 0.99. The overall linear fit of polyurethane acrylates' degradation kinetics yielded compensation effect parameters almost identical for degradation in nitrogen and air: in O-2 ln A(0) = 0.12E(a) + 3.2 with R-2 = 0.97; in N-2 lnA(0) = 0.12E(a) + 3.1 with R-2 = 0.82. The compensation effect equation for diffusion-controlled evaporation of N-methyl pyrrolidone from the poly(urethane acrylates) with different crosslink densities was ln D-0 = 0.38 E-a - 0.57 with R-2 = 0.98. Semi-empirical Lawson-Keyes equations of proportionality of activation enthalpy (and activation energy) and entropy of the process to activated volume were derived. Process entropy and enthalpy compensation relation existence was consequently confirmed for condense phase processes. Other theoretical approaches explaining compensation effect were discussed and found consistent with the explanation of kinetic compensation effect presented.