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 (λm) of the gels. We reveal that this enhancement of λm due to the slidable cross links is pronounced specifically in uniaxial stretching, while it is considerably modest in biaxial stretching. The sensitivity of λm to loading axiality becomes larger as the ring densities decrease. The corresponding difference in λm is markedly larger for the PR gels with low ring densities than that for the networks with fixed cross links. The exceptional sensitivity of λm to loading axiality unveils a previously unidentified aspect of the chain-supply mechanism based on slidable cross links.