Elastic behaviour and low-temperature specific heat of linear and reticulated amorphous polymers

The mechanical characteristics in the region of the primary relaxation and the low-temperature specific heats have been measured in linear (bisphenol-A-poly-carbonate and polyurethane) and reticulated (a fully cross-linked heterocyclic network) amorphous polymers. The behaviours revealed have been analysed in order to throw light on their correlation to the polymer morphology. It is found that a cross-linked polymer shows values of fragility, anharmonicity and low-temperature specific heat which are significantly smaller than those of linear polymers, characterized by weak interchain interactions. It is also shown that the fragility appears to scale with the anharmonicity of the system, the less fragile polymer being characterized by the smallest degree of anharmonicity.