Case of Volatile Reaction Products

A cure reaction yielding volatile products, such as water in step-growth condensation reactions, should always be examined in sealed pans withstanding high internal pressure to obtain accurate kinetic data. In pans with loose fitting lids, the endothermic evaporation of volatile products is sometimes sufficiently large to compensate for the exothermic heat of reaction. Moreover, it is impossible to obtain quantitative data when sample mass is continuously changing by loss of volatile products. 

The interval of appropriate isothermal cure temperatures is limited. At too low cure temperatures, the reaction time is too long and the corresponding heat flow data may not exceed baseline noise. At too high cure temperatures, the reaction time is too short, so that a significant degree of conversion is unrecorded in the equilibration period at the start of the experiment. 

The sample can be immediately inserted into the DSC furnace, which is previously equilibrated at the desired curing temperature, or the sample can be placed into the DSC furnace at room temperature and then heated to the required temperature at a rapid but controlled rate. With both methods, however, some heat of reaction might remain unrecorded in the initial equilibration period and an extrapolation to zero time is needed for accurate kinetic data. 

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