Resorcinol-formaldehyde polycondensation; kinetics; kinetic equation; DSC

The kinetics of resorcinol-formaldehyde polycondensation was investigated by DSC. The resorcinol-formaldehydepolycondensation 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 mixtureswere heated from 10 to 100 C at five different heating rates (0.5-2.5 C min-1). The two obtained DSC peaks correspondwith two reaction steps (formation of hydroxymethyl derivatives of resorcinol and polycondensation reaction itself). Theoverall reaction heat evolved during both steps corresponds to 97-104 kJ mol-1 for all mixtures. Based on the kineticanalysis, the first reaction step is best fitted by the second-order kinetic model and its rate is controlled by chemicalreaction. The second reaction step can be described by R3 mechanism and is probably limited by diffusion in more viscoussolution. Found kinetics equation allows to predict the composition of reaction mixture during the polycondensation at leastat micro-scale. The obtained results can be useful for prediction of reaction course which can control the porosity ofresorcinol-formaldehyde gels.