A peculiar rubber elasticity feature of polyrotaxane (PR) gels with cross-links capable of moving along network strands is revealed by general biaxial strain testing that varies the strains in the two orthogonal directions. The influence of the strain in one direction on the stress in the other direction in the PR gels with sufficiently low cross-link concentrations is much smaller than that in conventional elastomers and gels with fixed cross-links. The stress-strain behavior of the PR gels under various types of deformation is exceptionally close to the prediction of the neo-Hookean model with no explicit strain-coupling between the different principal directions other than that resulting from volume conservation. The minimal strain-coupling between different two directions is a pronounced feature for PR gels with movable cross-links to vary the network topology in response to imposed deformation.
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