Bimodal elastomeric networks extensibility

Equi-biaxial extension results have been obtained by inflating sheets of unimodal and bimodal networks of PDMS [114,115]. Upturns in the modulus were found to occur at high biaxial extensions, as expected. Also of interest, however, are pronounced maxima preceding the upturns. Such dependences represent a challenging feature to be explained by molecular theories addressed to bimodal elastomeric networks in general. 

Xu P, Mark JE. Biaxial extension measurements on bimodal elastomeric networks. J Polym Sci Polym Phys Ed 1991 29 355-8. 

One of the most interesting types of model networks is the bimodal, which consists of very short chains intimately end linked with the much longer chains that are representative of elastomeric materials (32,66,68 72). These materials have unusually good elastomeric properties, specifically large values of both the ultimate strength and maximum extensibility. Possibly the short chains contribute primarily to the former, and the long chains primarily to the latter. Also, not only do short chains improve the ultimate properties of elastomers, but long chains improve the impact resistance of the much more heavily cross-linked thermosets. 

---