Marked Sensitivity of Ultimate Elongation to Loading Axiality in Polyrotaxane Gels with Largely Slidable Cross Links

Polyrotaxane (PR) gels with low ring densities have figure-of-eight cross links that can slide along network strands. The slidable cross links have a unique ability to increase the network strand length between adjacent cross links in the loading direction via chain supply from the stress-free direction, thereby enhancing the ultimate elongation (λ_m) of the gels. We reveal that this enhancement of λ_m due to the slidable cross links is pronounced specifically in uniaxial stretching, while it is considerably modest in biaxial stretching. The sensitivity of λ_m to loading axiality becomes larger as the ring densities decrease. The corresponding difference in λ_m is markedly larger for the PR gels with low ring densities than that for the networks with fixed cross links. The exceptional sensitivity of λ_m to loading axiality unveils a previously unidentified aspect of the chain-supply mechanism based on slidable cross links.