Thermal Analysis of Polymers
This chapter considers methods for measuring thermal properties, and their dependence on molecular-structure parameters. The discussion is limited to the properties of glass transition temperature, the crystalline melting point, specific heat and enthalpy, thermal conductivity, and thermal degradation. The influences on the glass transition of molecular weight, branching, cross-linking, copolymerization, and diluents or plasticizers can be accounted for by the free-volume theory. Thermal analysis of polymers is effectively done using the technique of differential scanning calorimetry (DSC). The basic differences between Differential thermal analysis and DSC lie in the design of the heating system and the mode of operation of the instrument. In DSC, the sample and reference are heated separately by individually controlled elements. The calculation of enthalpy from DSC differs depending on whether the transition is slow enough that a steady-state condition is maintained or so rapid that the change of the sample temperature is halted until sufficient heat is supplied.