Formation and Self-Organization Kinetics of α-CD/PEO-Based Pseudo-Polyrotaxanes in Water. A Specific Behavior at 30 °C

Abstract

alpha-Cyclodextrins (alpha-CDs) have the ability to form inclusion complexes with poly(ethylene oxide) (PEO) polymer chains. These pseudo-polyrotaxanes (PPRs) can be obtained by quenching an alpha-CD/PEO mixture in water from 70 degrees C down to a lower temperature (typically in the range from 5 to 30 degrees C) thanks to favorable interactions between alpha-CD cavities and PEO chains. Moreover, starting from a liquid alpha-CD/PEO mixture at a total mass fraction of 15% w/w at 70 degrees C, the formation of PPRs with time at a lower temperature induces a white physical gel with time, and phase separation is observed. We established that PPR molecules are exclusively found in the precipitated phase although unthreaded alpha-CD molecules and unthreaded PEO chains are in the liquid phase. At 30 degrees C, the physical gel formation is much slower than at 5 degrees C. At 30 degrees C, we established that, in a first step, alpha-CDs thread onto PEO chains, forming PPR molecules which are not in good solvent conditions in water. At a higher length scale, rapid aggregation of the PPR molecules occurs, and threaded alpha-CD-based nanocylinders form (cylinder length L = 5.7 nm and cylinder radius R = 4.7 nm). At a higher length scale, alpha-CD-based nanocylinders associate in a Gaussian way, engendering the formation of precipitated domains which are responsible for the high turbidity of the studied system. At the end of this first step (i.e., after 20 min), the system still remains liquid and the PPRs are totally formed. Then, in a second step (i.e., after 150 min), the system undergoes its reorganization characterized by a compacity increase of the precipitated domains and forms a physical gel. We found that PPRs are totally formed after 20 min at 30 degrees C and that the system stays in a nongel state up to 150 min. This opens new perspectives regarding the PPR chemical modification: between these two characteristic times, we can easily envisage an efficient chemical modification of the PPR molecules in water, as for instance an end-capping reaction leading to the synthesis of polyrotaxanes.

Star-Pseudopolyrotaxane Organized in Nanoplatelets for Poly(ε-caprolactone)-Based Nanofibrous Scaffolds with Enhanced Surface Reactivity

“…In agreement with macroscopic observations, the scattered intensity profi le of starpPRs was constant during more than 7 h showing the high stability of the structures formed in DMSO at 35 °C. A similar behavior was already observed for other types of pPR [ 14,15 ] or polyrotaxane [ 16 ] for which lateral association between the rotaxane portions led to self-organization in nanobundles or nanoplatelets. By analogy, a parallelepiped model was used to fi t the SANS data.…”

Supramolecular cyclodextrin-based drug nanocarriers

“…Association of the threaded CDs from adjacent polypseudorotaxanes may lead to phase separation or to a three-dimensional network, depending on the polymer and its 35 concentration as well as on the temperature and ions content of the medium. 77,87,88 Interestingly the inter-polypseudorotaxane interactions are minimized when hydrophilic derivatives of the natural CDs are used; namely, hydroxypropyl-CDs can thread onto the polymers but do not stack. Thus, they form hydrosoluble 40 polypseudorotaxanes that do not significantly modify the turbidity/viscosity of the system.…”

Tough polypseudorotaxane supramolecular hydrogels with dual-responsive shape memory properties

“…3b clearly show that there are no NOE correlation peaks between the protons of PEGMA and H3/H5 of a-CD, which point to the internal cavity of a-CDs, indicating that a-CDs do not thread onto PEGMA chains before polymerization at 60 1C in the presence of AM. 37 These experiments demonstrate that both high temperature and acrylamide are vital to obtain a homogeneous solution in the hydrogel preparation process. Polypseudorotaxane aggregates and a precipitate will appear either at room temperature or without the presence of acrylamide.…”