The Glass Temperature


This chapter presents a discussion on glass temperature Tg of polymers. The Tg of a given polymer depends on the rate of cooling, q, the pressure, P, the number average molecular weight, Mn, and if in solution, its volume fraction, Φ2. For a polycrystalline polymer, changes of Tg occur with a variation of the degree of crystallinity and the nature of the morphology of the material. The effect of each of these experimental variables are discussed with minimal reference to model-dependent analyses. The emphasis is on the phenomenology that has been observed. The free volume, entropy, coupling, and fictive temperature models have all been used in analyzing the phenomena with conflicting results in many cases. Tg as the intersection point of the volume, y, or enthalpy, H, temperature lines of the equilibrium (or metastable equilibrium) liquid and the glass obtained in cooling are shown in a figure. Crosslinking can increase the Tg above that of the infinite molecular weight linear polymer. The viscoelastic behavior of an amorphous nonpolymeric dehydroabietic acid DHAA as seen at the Tg along with that of a low molecular weight unentangled polystyrene and a high molecular weight entangled polystyrene has been shown in the form of many of the commonly presented functions. The relaxation strength, Δϵβ, of the JG relaxation in all glass-formers is found to change on heating through the Tg in a similar manner as the changes observed in the enthalpy H, entropy S, and volume V.

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The Glass Temperature
Book Title
Physical Properties of Polymers Handbook
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  • James E. Mark Send Email (1)
  • Editor Affiliation
  • 1 Department of Chemistry, University of Cincinnati, Crosley Tower, Martin Luther King Drive, 45221-0172, Cincinnati, OH
  • Authors
  • Donald J. Plazek Send Email (2)
  • Kia L. Ngai Send Email (3)
  • Author Affiliation
  • 2 Department of Materials Science and Engineering, University of Pittsburgh, 15261, Pittsburgh, PA
  • 3 Naval Research Laboratory, 6807, 20375-5320, Washington, DC
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