Elastomers without Covalent Cross-Linking: Concatenated Rings Giving Rise to Elasticity

There is intense interest in making mechanically stable elastomers with properties resembling those of human muscles for use in soft robotics. Recently, a polydimethylsiloxane (PDMS) elastomer prepared without the use of cross-linking moieties from heterobifunctional PDMS macromonomers of intermediate molecular weight has been shown to exhibit surprising inherent softness and excellent stability upon both large deformation and swelling, in clear contradiction of classical rubber elasticity theories. In this work, this unexpected elasticity is shown to originate from concatenated rings.