Regulation of Sol Viscosity and Gel Elasticity in Thermoresponsive Polyrotaxane Block Copolymers via Tunable Macrocycle Coverage

Thermoresponsive polymers often face a trade-off between low sol viscosity and high gel elasticity because interchain entanglements contribute differently to the two states. Here, we report PNIPAM-b-PEG-b-PNIPAM-based polyrotaxane block copolymers with precisely controlled coverage of cyclodextrin-derived macrocycles. Macrocycle coverage is regulated during threading through kinetic regulation by terminal ATRP initiator groups and thermodynamic regulation by cyclodextrin derivatization, followed by ATRP end-capping. In 20 wt % aqueous solutions, copolymers bearing 22 and 32 macrocycles per chain exhibit apparent viscosities of ∼1% and ∼0.1% of the nonthreaded control, respectively; the resulting gels show storage moduli above 3000 Pa and >900-fold modulus enhancement from 25 to 40 °C, with thermal hysteresis decreasing as macrocycle coverage increases. These results suggest that macrocycles dynamically slide along the PEG segment in the sol state and may translocate during gelation, forming mobile rigid domains that modulate backbone accessibility for interchain entanglement.