Threading Different Rings on X‑Shaped Block Copolymers: Hybrid Pseudopolyrotaxanes of Cyclodextrins and Tetronics

• Published in: Macromolecules Vol. 53; no. 8; pp. 3166 - 3174
• Main Authors: Puig-Rigall, Joan, Serra-Gómez, Rafael, Guembe-Michel, Nerea, Grillo, Isabelle, Dreiss, Cécile A, González-Gaitano, Gustavo
• Format: Journal Article
• Language: English
• Published: American Chemical Society 28.04.2020
• ISSN: 0024-9297; 1520-5835
• DOI: 10.1021/acs.macromol.0c00409

Pseudopolyrotaxanes (PPRs) are supramolecular host–guest complexes constituted by the reversible threading of macrocycles along a polymer chain. We report the formation of hybrid PPRs (hPPRs), where two types of cyclodextrins (CDs) thread either simultaneously or sequentially on four-arm poly­(ethylene oxide)–poly­(propylene oxide) (PEO–PPO) block copolymers (Tetronic): native α-CD (CD) (with higher affinity for PEO) and dimethylated β-CD (DIMEB, with higher affinity for PPO). The competitive complexation along the chains is examined with three Tetronics, differing mainly in the length of their PEO blocks: T904, T1107, and T1307. While PPRs formed with α-CD are insoluble, due to the hydrogen-bond network formed between adjacent α-CDs, the presence of DIMEB leads to soluble hybrid PPRs, slows down the kinetics of complexation, and increases the number of α-CDs threaded per arm. The morphology of the constructs in solution over time is followed by time-resolved small-angle neutron scattering (TR-SANS), while their crystalline structure is studied by X-ray diffraction. Whereas the complexation of the polymeric surfactant with DIMEB shifts the unimer–micelle equilibrium toward unimers, the presence of α-CD slows down demicellization and reduces its extent. Overall, the co-threading of two cyclodextrins on the same polymer provides a handle to tune the complexation process and the final properties of the PPR, including solubility, kinetics of complexation, and composition of the complexes.