Self-assembled Structure of Polyrotaxane Consisting of β-Cyclodextrin and Poly(ethylene oxide)-block-poly(propylene oxide)-block-poly(ethylene oxide) Triblock Copolymer in Bulk System

Abstract

Polyrotaxanes consisting of β-cyclodextrin (β-CD) and poly(ethylene oxide)-block-poly(propylene oxide)-block-poly-(ethylene oxide) (PEO-PPO-PEO) triblock copolymer endcapped with bulky trityl groups were synthesized for the first time. Self-assembled structures of the bulk sample cast from water and dimethyl sulfoxide (DMSO) based on the crystal structure of β-CD molecules and triblock copolymer microphase separation were investigated using small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD). It was found that microphase-separated structures of a different periodic distance were formed depending on the casting solvent.Keywords: Polyrotaxane | Cyclodextrin | Self-assembled structure Supramolecular systems 16 based on noncovalent interactions, such as hydrogen bond, van der Waals force, and dipole interaction, have attracted great interest because of their ability to form complex self-assembled structures by designing chemical structures and preparation pathways. For supramolecular polymers, 710 it has been shown that self-assembled structures can remain trapped at thermodynamically unstable states depending on the pathway selected for the preparation method. 11It has recently turned out that the architectures formed by a different pathway potentially shows a unique property based on their self-assembled structure.12 Cyclodextrins (CDs), which are cyclic host molecules, form supramolecular complexes by including a variety of guest molecules, because of the hydrophilicity of its exterior and the relative hydrophobicity of its interior. 13 The inclusion complexes of CD have been well studied and paid attention to be applied for materials in different areas. 14,15 Rotaxane, which consists of a cyclic molecule threaded onto a linear polymer axis end-capped with bulky moieties, was first reported by Harrison and Harrison. 16 In 1992, the facile synthesis of polyrotaxane, which has two or more cyclic molecules, was achieved by just mixing α-CD and poly(ethylene glycol) (PEG) in aqueous solution, to form their inclusion complex and subsequent end-capping of the backbone PEG with bulky groups. 17 More recently, switching of the location of CDs along the polymer axis has been performed by changing temperature.18,19 Thus, it seems that polyrotaxanes made by CDs are one of the best supramolecular polymer systems to tune the self-assembled structure by changing the preparative pathway.Recently However, little attention has been paid to the microphaseseparated structure. Here, we report a crystal structure of CDs and microphase-separated structures formed in a newly synthesized polyrotaxane consisting of β-CD and PEO-PPO-PEO triblock copolymer (Pluronic F68; PEO 76 PPO 29 PEO 76 , M w = 8.4 kg mol ¹1), which depends on the casting solvents. The synthetic scheme of the polyrotaxane consisting of β-CD and Pluronic F68 is shown in Scheme 1. Firstly, N-trityl-1,6-diaminohexane, an end-capping agent, was synthesized following a reported procedure with a slight modification. 25 Next, the hydroxy groups of t...

Precision synthesis of linear oligorotaxanes and polyrotaxanes achieving well-defined positions and numbers of cyclic components on the axle

“…Polyrotaxane 27 was synthesized via self-assembly between b-cyclodextrins (b-CDs) and the block-polymer, in which the b-CDs were localized on the PPO segments, followed by a capping reaction with bulky stopper units at both ends of the assembled axle. 79,80 The b-CDs on the polyrotaxane were chemically modified with a hydrophilic hydroxypropyl moiety to form 28, followed by modification with a hydrophobic trimethyl silyl group to afford 29. In the bulk material, 28 formed a melted state at high temperatures (Fig.…”

Topology-transformable polymers: linear–branched polymer structural transformation via the mechanical linking of polymer chains

“…Furthermore, they revealed the prominent properties and wide applicability via the preparation of various slide-ring gels. [99][100][101][102][103][104][105] These pioneering works were followed by a variety of studies in which the movable junction point played a crucial role. [106][107][108][109][110][111][112][113][114][115][116][117][118][119][120][121][122] In these reports on RCPs, the number of wheel components utilized for the crosslink points and their movable length or range on the axle …”

Molecular Recognition of Fluorescent Probe Molecules with a Pseudopolyrotaxane Nanosheet

“…Very recently the formation of a pseudopolyrotaxane nanosheet (PPRNS) was reported, which is the nanosheet material fabricated via a supramolecular self-assembly between the CD and the polymer. − A representative PPRNS is obtained by complexation between β-CD and a carboxyl-terminated poly­(ethylene oxide) 75 - block -poly­(propylene oxide) 29 - block -poly­(ethylene oxide) 75 (COOH-EO 75 PO 29 EO 75 ) triblock copolymer. , β-CD can selectively cover the central PO segment and form nanosheets with a thickness of 11 nm, which corresponds to the extended length of 29 PO units. This nanosheet has a well-defined rhombus shape, reflecting the single crystal structure of β-CD .…”

“…18,20−22 Very recently the formation of a pseudopolyrotaxane nanosheet (PPRNS) was reported, which is the nanosheet material fabricated via a supramolecular self-assembly between the CD and the polymer. 23 23,26 β-CD can selectively cover the central PO segment and form nanosheets with a thickness of 11 nm, which corresponds to the extended length of 29 PO units. This nanosheet has a well-defined rhombus shape, reflecting the single crystal structure of β-CD.…”