Mechanically Linked Block/Graft Copolymers: Effective Synthesis via Functional Macromolecular [2]Rotaxanes

An effective method to synthesize mechanically linked transformable block polymer was developed utilizing functional macromolecular [2]­rotaxane with a “fixed” or “movable” wheel. The interaction between a <i>sec</i>-ammonium and a dibenzo-24-crown-8-ether was the key to control the mobility of the wheel component, indicating the capability of the transformation from linear block copolymer to block/graft copolymer in which the grafting polymer chain is movable along the axle polymer chain

Synthesis and Star/Linear Topology Transformation of a Mechanically Linked ABC Terpolymer

The synthesis of an ABC star terpolymer containing one polymer chain connected mechanically through a rotaxane linkage and its topology transformation to a linear structure are reported. Pseudo[2]­rotaxane, which was designed as the key trifunctional species for the star polymer synthesis, comprised a <i>sec</i>-ammonium axle with ethynyl and hydroxy groups and a crown ether wheel with a trithiocarbonate group. Stepwise polymer connections to the pseudo[2]­rotaxane using the three groups afforded a rotaxane-linked ABC star terpolymer. The topology transformation from star to linear by the removal of the attractive interaction between the axle and wheel components yielded a linear ABC terpolymer via the wheel shifting to the axle end. The spectroscopic and solution property changes clearly indicated the occurrence of the polymer topology change

Polyester-Containing α‑Cyclodextrin-Based Polyrotaxane: Synthesis by Living Ring-Opening Polymerization, Polypseudorotaxanation, and End Capping Using Nitrile <i>N</i>‑Oxide

The first synthesis of polyrotaxanes consisting of polyester axles and α-cyclodextrin (α-CD) wheels was achieved by the catalyst-free click end-capping reaction of polypseudorotaxanes using nitrile <i>N</i>-oxide. The polypseudorotaxanes contain acrylate-functionalized polyesters that are obtained by the living ring-opening polymerization of lactones. The yield and coverage ratio of polyrotaxanes are highly dependent on the reaction time, molecular weight of the polyester, polyester structure, and solvent used. From the thermal properties of the resulting polyrotaxanes, it was found that coverage with α-CDs efficiently suppresses the crystallization of the polyester main chain

Click Annulation of Pseudo[2]rotaxane to [2]Catenane Exploiting Homoditopic Nitrile <i>N</i>‑Oxide

A mild annulation reaction of a propargyl-terminated pseudorotaxane with a homoditopic stable nitrile <i>N</i>-oxide enabled the efficient synthesis of catenanes consisting of not only dibenzo-24-crown-8-ether (DB24C8) but also dibenzo-30-crown-10-ether (DB30C10) as a wheel component. A dynamic ¹H NMR study showed the highly enhanced mobility of the components of the DB30C10-based [2]catenane due to the enlarged wheel cavity

Catalyst- and Solvent-Free Click Synthesis of Cyclodextrin-Based Polyrotaxanes Exploiting a Nitrile <i>N</i>-Oxide

A catalyst- and solvent-free synthesis of cyclodextrin-based polyrotaxanes exploiting a stable nitrile <i>N</i>-oxide as an end-capping agent was achieved. The C–C bond-forming end-capping reaction of an allyl-terminated pseudopolyrotaxane with the nitrile <i>N</i>-oxide proceeded smoothly by solid-state grinding in a mortar to afford a polyrotaxane

Intramolecular 1,3-Dipolar Cycloaddition of Nitrile <i>N</i>-Oxide Accompanied by Dearomatization

Intramolecular 1,3-dipolar cycloaddition of 2-phenoxybenzonitrile <i>N</i>-oxides to benzene rings, accompanied by dearomatization, formed the corresponding isoxazolines in high yields. The X-ray single-crystal structure analysis revealed that the reaction formed the <i>cis</i>-adduct as a single isomer. The substituents on the benzene rings markedly affected the reaction rate, yield, and structure of the final product

A Rational Entry to Cyclic Polymers via Selective Cyclization by Self-Assembly and Topology Transformation of Linear Polymers

A simple and effective synthetic route to cyclic polymers has been developed based on the following sequence: (i) selective cyclization of two self-complementary <i>sec-</i>ammonium-containing crown ether monomers to afford [c2] daisy-chain bifunctional initiators, (ii) living polymerization to afford the corresponding linear polymers, and (iii) a topology transformation of these linear polymers to furnish cyclic polymers. The key step in this sequence is the quantitative cyclization via self-assembly of two crown ether molecules with hydroxyl and <i>sec-</i>ammonium moieties. After the living polymerization, the linear polymers release the daisy-chain assembly to generate a cyclic topology. The specific advantages of the present synthetic protocol, i.e., procedural simplicity and concentration independence, are demonstrated by a gram-scale synthesis

Synthesis of Highly Reactive Polymer Nitrile <i>N</i>‑Oxides for Effective Solvent-Free Grafting

A one-pot synthesis of polymer nitrile <i>N</i>-oxides was achieved via the Michael addition of living polymer anions derived from vinyl monomers to commercially available <i>trans</i>-β-nitrostyrene and subsequent dehydration with concd H₂SO₄. The polymer nitrile <i>N</i>-oxides are effective as grafting agents in catalyst- and solvent-free 1,3-dipolar cycloadditions to unsaturated-bond-containing polymers with high conversion and exhibit higher reactivity compared to that of nitrile <i>N</i>-oxides prepared from 1,1-diphenylnitroethene. Application to the preparation of a functional glass surface was demonstrated using P<i>t</i>BMA nitrile <i>N</i>-oxide as a grafting agent

Fluorescence Control of Boron Enaminoketonate Using a Rotaxane Shuttle

The effect of rotaxane shuttling on the fluorescence properties of a fluorophore was investigated by exploiting fluorophore-tethered [2]rotaxanes. A fluorescent boron enaminoketonate (BEK) moiety was introduced in a rotaxane via transformation of an isoxazole unit generated as a result of an end-capping reaction using a nitrile <i>N</i>-oxide. The rotaxane exhibited a red shift of the fluorescence maximum along with a remarkable enhancement of the fluorescence quantum yield through wheel translation to the fluorophore

Selective Synthesis of a [3]Rotaxane Consisting of Size-Complementary Components and Its Stepwise Deslippage

An α-cyclodextrin-based size-complementary [3]rotaxane with an alkylene axle was selectively synthesized in one pot via an end-capping reaction with 2-bromophenyl isocyanate in water. Thermal degradation of the [3]rotaxane product yielded not only the original components but also the [2]rotaxane. Thermodynamic studies suggested a stepwise deslippage process