Self-assemblies of γ-CDs with pentablock copolymers PMA-PPO-PEO-PPO-PMA and endcapping via atom transfer radical polymerization of 2-methacryloyloxyethyl phosphorylcholine

Abstract

SummaryPentablock copolymers PMA-PPO-PEO-PPO-PMA synthesized via atom transfer radical polymerization (ATRP) were self-assembled with varying amounts of γ-CDs to prepare poly(pseudorotaxanes) (PPRs). When the concentration of γ-CDs was lower, the central PEO segment served as a shell of the micelles and was preferentially bent to pass through the γ-CD cavity to construct double-chain-stranded tight-fit PPRs characterized by a channel-like crystal structure. With an increase in the amount of γ-CDs added, they began to accommodate the poly(methyl acrylate) (PMA) segments dissociated from the core of the micelles. When more γ-CDs were threaded and slipped over the segments, the γ-CDs were randomly distributed along the pentablock copolymer chain to generate single-chain-stranded loose-fit PPRs and showed no characteristic channel-like crystal structure. All the self-assembly processes of the pentablock copolymers resulted in the formation of hydrogels. After endcapping via in situ ATRP of 2-methacryloyloxyethyl phosphorylcholine (MPC), these single-chain-stranded loose-fit PPRs were transformed into conformational identical polyrotaxanes (PRs). The structures of the PPRs and PRs were characterized by means of 1H NMR, GPC, 13C CP/MAS NMR, 2D 1H NOESY NMR, FTIR, WXRD, TGA and DSC analyses.

How Does PHEMA Pass through the Cavity of γ-CDs to Create Mismatched Overfit Polypseudorotaxanes?

“…Equilibria between the threading and dethreading of γ-CDs were reached after nearly 48 h, but there was still no precipitation observed even after 5 days of incubation at each feeding ratio. These results clearly revealed that the self-assembly of γ-CDs with PHEMA indeed took place, but it is a time-consuming process in which both of them should be mutually and dynamically adapted to each other and should change their conformations to promote PHEMA squeezing and passing through the evidently unfittable cavity of γ-CDs to construct mismatched overfit PPRs instead of matched tight-fit ones as schematized in Figure due to the obviously thicker cross-sectional area and the stereoregularity of PHEMA. ,− …”

“…Compared to atactic polystyrene ( a -PS), poly­(methyl metha­crylate) ( a -PMMA), and poly­(propylene oxide) (PPO), , a full extended a -PHEMA chain is thicker than either PPO or a -PS and a -PMMA, and it would hold such a huge cross-sectional area that it seemingly cannot pass through the cavity of γ-CDs; therefore, it can be used as a bulky stopper to end-cap PPRs even though γ-CD possesses a relatively wider inner cavity compared to its α- and β-CD counterparts. However, in our recent reports, γ-CDs were found to include not only PNIPAAm-PPO-PEO-PPO-PNIPAAm but also PHEMA-PPO-PEO-PPO-PHEMA to construct PPRs featuring unique inclusion complexation architectures. − For example, attaching PNIPAAm or PHEMA blocks alters the recognition evolution direction of γ-CDs with PPO-PEO-PPO in these PPRs, in which γ-CDs are mismatchedly threaded onto and surmount the flank PHEMA blocks to generate a single-straight-chain stranded PPR exhibiting the loose-fit (PEO) and overfit (PHEMA) crystal structures instead of a double-bent-chain-stranded PPR showing the matched tight-fit (PEO) one . After the in situ atom transfer radical polymerization (ATRP) of 2-meth­acryloyl­oxy­ethyl phos­phoryl­choline (MPC) initiated with those PPRs as macroinitiators in aqueous solution, the corresponding PR-based multiblock copolymers were synthesized. , Therefore, besides the hydrogen bond and hydrophobic, van de Waals, and dipole–dipole interactions, crucial factors such as the deformation of γ-CDs via possible tumbling or the inversion of glycopyranose units, the stereoregularity of polymeric chains, and the mutual adapability of polymeric side chain with the inner cavity geometry of γ-CDs could play dominant roles in the formation of mismatched overfit PPRs from the obviously unfavorable self-assembly of γ-CDs with a thicker polymeric main chain. , To the best of our knowledge, there are a limited number of research papers devoted to the self-assembly of γ-CDs with PHEMA and its copolymers. − Therefore, it is highly desirable to understand how the thicker PHEMA chain adapts its conformation to squeeze and pass into the cavity of γ-CDs to give rise to the mismatched overfit PPRs.…”

Preparation of stereocomplex and pseudo-polyrotaxane with various cyclodextrins as wheel components using triblock copolymer of poly(ethylene glycol) and polylactide

“…Considering that γ-CD can contain two PEGs, we carefully considered the ratio of PEG and CD, and the values in Table 1 were estimated with the assumption that one γ-CD was present on one axis. On the other hand, it is possible to form core–shell micelles 66 on the PPRX preparation, and the central moiety of PEG in the triblock copolymer locate outside with bent form, resulting in the double stranded hydrophilic PEG which allows more effective introduction of γ-CD than α- and β-CD due to the ring size.…”

Synthesis of Poly(Methyl Methacrylate)-Based Polyrotaxane via Reversible Addition–Fragmentation Chain Transfer Polymerization

“…Therefore, a synthesis method with a suitable molecular design needs to be developed. In the case of controlled polymerization, Feng et al performed atom transfer radical polymerization as a way to prepare PR and the self-assembly behaviors were investigated …”

“…In the case of controlled polymerization, Feng et al performed atom transfer radical polymerization as a way to prepare PR and the self-assembly behaviors were investigated. 8 On the other hand, reversible addition−fragmentation chain transfer polymerization (RAFT) was also utilized to synthesize PR. In a previous study, RAFT was only applied for the extension on the chain ends while the central PEG segment length in the main chain remains the same.…”