LOW TEMPERATURE SPECIFIC HEAT OF HETEROCYCLIC POLYMER NETWORKS: EFFECT OF NETWORK DENSITY
Résumé
Measurements of low frequency Raman scattering and low temperature specific heat between 2 and 20 K have been performed in two glassy, heterocyclic polymer networks. The effective network densities of heterocyclic polymer networks are varied by changing the ratio of bi- and mono-functional isocyanate monomers leaving the overall chemical structure essentially unchanged. A boson peak at about 20 cm-1 characterizes the Raman spectra at room temperature of both the samples. Below 10 K, the specific heats deviate from a cubic temperature dependence, as predicted by the Debye theory, and reveal an excess specific heat having the shape of a well-defined peak in a Cp/T3 plot with a maximum at about 5 K. The increase of the effective network density is accompanied by a slight decrease of the excess specific heat. These observations have been explained in terms of additional low-energy vibrations associated to the monomers building up the polymer networks.
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