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- Glass transition : process in which a polymer melt changes on cooling to a polymer glass or a polymer glass changes on heating to a polymer melt.
# Phenomena occurring at the glass transition of polymers are still subject to ongoing scientific investigation and debate. The glass transition presents features of a second-order transition since thermal studies often indicate that the molar Gibbs energies, molar enthalpies, and the molar volumes of the two phases, i.e., the melt and the glass, are equal, while the heat capacity and the expansivity are discontinuous. However, the glass transition is generally not regarded as a thermodynamic transition in view of the inherent difficulty in reaching equilibrium in a polymer glass or in a polymer melt at temperatures close to the glass-transition temperature.
# In the case of polymers, conformational changes of segments, typically consisting of 10–20 main-chain atoms, become infinitely slow below the glass transition temperature.
# In a partially crystalline polymer the glass transition occurs only in the amorphous parts of the material.
# The definition is different from that in ref.
# The commonly used term “glass-rubber transition” for glass transition is not recommended. (en)
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