Topological Stress Dissipation in Amorphous Elastomers Crosslinked by Polyrotaxanes with Poly(ε-Caprolactone-co-δ-Valerolactone) Side-Chains.

Sliding elastomers (SE) based on polyrotaxane (PR) architectures exhibit exceptional mechanical toughness through the "pulley effect". However, side-chain crystallization in such solvent-free systems often compromises molecular mobility and the efficiency of the topological cross-links. In this study, a series of solvent-free sliding elastomers was developed by grafting amorphous poly(ε-caprolactone-co-δ-valerolactone) [P(CL-co-VL)] side chains that are amorphous at ambient conditions onto a hydroxypropylated polyrotaxane (HPR) backbone via ring-opening polymerization. Systematic investigations were conducted by varying the side-chain degrees of polymerization (DP = 13, 26, 52) and the cross-linking indices (r = [NCO]/[OH]). The amorphous nature of the random copolymeric side chains effectively suppressed crystallization, thereby facilitating the unhindered sliding motion of α-cyclodextrin rings along the PEG axis. Compared to traditional fixed covalent cross-linking initiated by hydroxypropyl β-cyclodextrin (HPCD), these solvent-free elastomers exhibited superior mechanical performance, achieving a tensile strength of 10.2 MPa and an exceptional elongation at break of 830%. It is demonstrated that the synergy between topological sliding cross-links and the amorphous side-chain design allows for precise tuning of mechanical responses and stress homogenization. This work provides a robust strategy for the fabrication of high-performance, solvent-free topological elastomers with an optimized "pulley effect" for advanced flexible applications.