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.KEY WORDS: Elastomers / Gels / Rubber Elasticity / Rheology / Reptation / Entanglements / Crosslinked polymer networks composed of flexible strands exhibit many unique properties that stem from their threedimensional network structures: they behave as soft solids because they do not flow macroscopically owing to the presence of crosslinks, but they still possess a liquid nature due to the weak constraints at the crosslinks, allowing the micro-Brownian motion of network strands. Rubber elasticity-reversible large deformability under small external forces-is one of the salient characteristics of polymer networks, and hence, they are often called ''elastomers.'' Elastomers are widely employed in industry, and the fundamental aspects of their physical properties have been extensively investigated over the past half century.1,2 The molecular understanding of their physical properties, however, still remains incomplete because their network structures are not well characterized:3 the rubbery networks prepared by randomcrosslinking of the precursor chains have inhomogeneous structures with a broad length distribution of the network strands; in addition, the characterization of the strand length distribution in elastomers is not possible by current analytical techniques. However, end-linking end-reactive precursor chains of known molecular weight using multifunctional crosslinkers affords a tailor-made model network with a wellcharacterized structure. [4][5][6] To the first-order approximation (which is accurate in the case of the complete reaction), the...

Topological Interaction between Loop Structures in Polymer Networks and the Nonlinear Rubber Elasticity

“…This behavior can be also explained in terms of Eq. (19). The linking probability P L (ζ) for small r d continuously decreases as ζ increases as shown in Fig.…”

“…In Eq. (19), the elastic contributions from nontrivial and trivial links are determined by P L (ζ ′ ). Under small extensions, loops may be closely distributed to each other and their linking probability P L (ζ ′ ) should have a large average as seen in the numerical results in Fig.…”

“…(19) is proportional to (1 − P(ζ ′ )) −2 and takes a large value when P L (ζ ′ ) ∼ 1; whereas, the stress of the nontrivial links slightly changes because the λ-derivative of the first term in Eq. (19) is proportional to P(ζ ′ ) −2 .…”

Optimization Techniques for Improving the Performance of Silicone‐Based Dielectric Elastomers

“…In real networks, dangling substructures (mainly dangling chains) and so-called "sol polymer chains" exist. [111,112] Dangling substructures are defined as being attached covalently to the infinite network structure at one end only. Sol molecules, on the other hand, are not attached covalently to the infinite network structure.…”

Novel silane based cross-linkers for preparation of methyl methacrylate gels

“…There are many chemical and biomedical applications such as optics, electronics, mechanics and electrochemistry which require polymer gels with excellent absorption and mechanical properties [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16]. These materials are prepared mainly by freeradical copolymerization of monovinyl (MVM) and divinyl monomers (DVM) in a suitable solvent [17][18][19][20][21][22].…”