Proposal of Pseudo-Capping Effects by Polymer-Polymer Interaction through Preparation of Stereocomplex Pseudo-Polyrotaxane with Cyclodextrin and PEG-PLA Triblock Copolymers

ABA types triblock copolymers, specifically poly(L-lactide)-co-poly(ethylene glycol)-co-poly(L-lactide) (PLLA-PEG-PLLA) and poly(D-lactide)-co-poly(ethylene glycol)-co-poly(D-lactide) (PDLA-PEG-PDLA), are employed for stereocomplexes (SCs) formation. These SCs are subsequently utilized as axles, in conjunction with various cyclodextrins (CDs) as ring moieties to create pseudo-polyrotaxane (PPRX). The authors referred to this new construct as SC PPRX, to distinguish it from the earlier study, denoted as PPRX SC, which primarily focuses on SC within the PPRX. When attempting to form PPRXs in aqueous solutions, the authors encountered challenges related to the inclusion of CDs due to the robust presence of the SC structure. However, by using mixed solvents, such as water/acetone (10/1, v/v), a partial relaxation of the SC structure is observed. This allows for the successful inclusion of CDs, thereby facilitating the PPRX formation. These observations highlight the significance of axle-axle interaction, which, in this case, prevailed over axle-ring interactions in determining the outcome of the formation process. The authors propose the term, 'SC pseudo-capping effect' to describe this unique phenomenon, underscoring the role of interactions among polymer chains, including polymer-polymer and axle-axle interactions, in shaping the architecture of rotaxanes. This study thus unveils a novel dimension of polymer-polymer interactions within the realm of rotaxane. Poly(L-lactide)-co-poly(ethylene glycol)-co-poly(L-lactide) (PLLA-PEG-PLLA) and poly(D-lactide)-co-poly(ethylene glycol)-co-poly(D-lactide) (PDLA-PEG-PDLA) used for stereocomplex (SC) formation and the subsequent pseudo-polyrotaxane (PPRX) formation are investigated using alpha-, beta-, and gamma-cyclodextrins (CDs). A water and acetone mixed solvent allows SC PPRX formation, revealing the importance of axle-axle interactions in PPRX formation - referred to as the 'SC pseudo-capping effect.image

Automated summary

This study investigates the formation of stereocomplexes (SCs) using PLLA-PEG-PLLA and PDLA-PEG-PDLA, and the subsequent formation of pseudo-polyrotaxanes (PPRX) with alpha-, beta-, and gamma-cyclodextrins (CDs). The inclusion of CDs in aqueous solutions is challenging due to the strong SC structure, but can be achieved by using a mixed solvent. This study highlights the importance of axle-axle interactions in PPRX formation, termed the "SC pseudo-capping effect".