Kinetics of resorcinol-formaldehyde polycondensation by DSC

The kinetics of resorcinol-formaldehyde polycondensation was investigated by DSC. The resorcinol-formaldehyde polycondensation mixtures were prepared using different catalyst (Na2CO3) concentrations (molar ratio of resorcinol/catalyst R/C=25 and 50) and mass contents of reactants (w=20 and 40%). The studied polycondensation mixtures were heated from 10 to 100 degrees C at five different heating rates (0.5-2.5 degrees Cmin(-1)). The two obtained DSC peaks correspond with two reaction steps (formation of hydroxymethyl derivatives of resorcinol and polycondensation reaction itself). The overall reaction heat evolved during both steps corresponds to 97-104kJmol(-1) for all mixtures. Based on the kinetic analysis, the first reaction step is best fitted by the second-order kinetic model and its rate is controlled by chemical reaction. The second reaction step can be described by R3 mechanism and is probably limited by diffusion in more viscous solution. Found kinetics equation allows to predict the composition of reaction mixture during the polycondensation at least at micro-scale. The obtained results can be useful for prediction of reaction course which can control the porosity of resorcinol-formaldehyde gels.