Network Topology–Mechanical Properties Relationships of Model Elastomers

Abstract

We review our recent studies on the mechanical properties of model elastomers with well-characterized network structures. Model elastomers were prepared by end-linking precursor poly(dimethylsiloxane) (PDMS) of known molecular weight with multifunctional crosslinkers. We then strictly assessed the modern entanglement models for rubber elasticity on the basis of the stress–strain data under general biaxial strains covering almost the entire range of accessible deformations for the model PDMS networks. We also demonstrated marked extensibility of more than 3000% for the deswollen networks prepared by removing the solvent from the end-linked gels prepared in the diluted state. The highly deswollen networks comprising the considerably compact conformation (supercoil) exhibited unusually weak strain dependence of stress. We also studied the viscoelastic properties of PDMS networks containing either unattached free chains or pendant chains. The former systems provided a model system to investigate the dynamics of the guest chains in invariant networks. The dynamics of the guest chains, as functions of their own sizes as well as the mesh sizes of host networks, were compared with the predictions of reptation theories. With the model networks with pendant chains, we elucidated the correlation between the damping properties and the amount of pendant chains. The elastomers with highly irregular structures exhibited high damping almost independent of both temperature and frequency.