Equilibrium and dissipative properties in polymer networks with prescribed content of defects

VEGA DA

Dresden

Conferencia; Conferencia invitada; 2017

Leibniz Institute for Polymer Research Dresden

Trapped entanglements, crosslinker functionality and elastically effective chains are the sources of elasticity of polymer networks and gels. However, despite of more than eighty years of theoretical and experimental research in this field, there are still many open questions about their relative contribution to network elasticity. The structure and viscoelastic response of polymer networks are highly sensitive to the functionality of the cross-linkers and presence of soluble and pendant material. Defects, that are unavoidably produced during any cross-linking reaction, reduce the cross-linking density and affect the damping response of elastomers. In this work we employed swelling, rheology and double quantum nuclear magnetic resonance (DQ NMR) experiments to characterize the elasticity of model polymer networks prepared with cross-linkers of varying functionality and controlled contents of structural defects. We found that the contribution of trapped entanglements may equal the contribution coming from elastically active material and that it is independent of network topology. While the equilibrium behavior of the networks can be well described by the classical theories for rubber elasticity, the long time relaxational dynamics can be rationalized in terms of the tube model and the Pearson-Helfand picture for the arm retraction process.