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This is a review of glass transition temperature (Tg) measurements of materials by differential scanning calorimetry (DSC). Tg is noted in DSC derived heat capacity (Cp) plots against temperature as the jump in Cp or (∆Cp) that occurs usually over a temperature interval of a few tens of degrees (°C). Under conditions which are normal for DSC experiments it was found that the temperature gradient across and from top to bottom of a 0.6-mm-thick molded disk of polycarbonate (17 mg) was no greater than 0.6°C when heated at 15°C/min. Under these conditions a glassy polymer can be scanned for its Tg as defined by its half-vitrification temperature (½ ∆Cp) as well as the beginning and end of the transition to within 1°C. DSC Tg measurements are reviewed to show how the location, shape, and magnitude of the transition can be used to characterize the composition and behavior of a wide variety of polymeric materials ranging from homopolymers, blocks, grafts, and blends to networks. Also the effect of molecular weight, plasticizers, aging, crystals, and stress on the Tg of several polymers is re-examined.
glass transition temperature, fictive temperature, differential scanning calorimetry (DSC), polymer blends, blocks, grafts, plasticizers, physical aging, glass transition broadening, rigid amorphous phase
Member of technical staff, AT&T Bell Laboratories, Murray Hill, NJ