Nanoparticle-Based Tough Polymers with Crack-Propagation Resistance.

Although thin elastomer films of polymer nanoparticles are regarded as environmentally friendly materials, the low mechanical strength of the films limits their use in various applications. In the present study, we investigated the fracture resistance of latex films composed of acrylic nanoparticles where a small quantity of a rotaxane crosslinker was introduced. In contrast to conventional nanoparticle-based elastomers, the latex films composed of the rotaxane-crosslinked nanoparticles exhibited unusual crack propagation behavior; the direction of crack propagation changed from a direction parallel to the crack to one perpendicular to the crack, resulting in an increase in tear resistance.

Efficient Transformation of Polymer Main Chain Catalyzed by Macrocycle Metal Complexes via Pseudorotaxane Intermediate.

Post-synthesis modification of polymers streamlines the synthesis of functionalized polymers, but is often incomplete due to the negative polymer effects. Developing efficient polymer reactions in artificial systems thus represents a long-standing objective in the fields of polymer and material science. Here, we show unprecedented macrocycle-metal-complex-catalyzed systems for efficient polymer reaction that result in 100 % transformation of the main chain functional groups presumably via a processive mode reaction.

S nuclear quadrupole resonance study of dibenzyl disulfide toward understanding of cross-linked structures in rubber.

Experimental and theoretical investigations of a sulfur-33 electric-field-gradient (EFG) tensor of disulfide bonds in S-labled dibenzyl disulfide have been presented. Temperature dependence of quadrupolar frequencies, ν, is observed in the temperature range between 80 and 280 K, in which single peaks appear in all the S nuclear quadrupole resonance (NQR) spectra. Analysis of nutation echo S NQR spectra at 200 K yields the quadrupolar coupling constant, C value, of 46.

A supramolecular network derived by rotaxane tethering three ureido pyrimidinone groups.

A supramolecular network and its film were prepared via intermolecular hydrogen bonding of a [2]rotaxane with three ureido pyrimidinone groups. Adding less polar solvents such as CHCl to the rotaxane afforded a swollen rotaxane-cross-linked network. The properties of the film obtained by drying were evaluated to characterize it.

Induction of Single-Handed Helicity of Polyacetylenes Using Mechanically Chiral Rotaxanes as Chiral Sources.

Effective induction of preferred-handed helicity of polyacetylenes by pendant mechanically chiral rotaxanes is discussed. Polyacetylenes possessing optically active mechanically chiral rotaxanes in the side chains were synthesized by the polymerization of the corresponding enantiopure [2]rotaxane-type ethynyl monomers prepared by the chiral-phase HPLC separations. The CD Cotton effects revealed that the polyacetylenes took preferred-handed helical conformations depending on the rotaxane chirality.

Gold-Catalyzed Enantioselective Synthesis, Crystal Structure, and Photophysical/Chiroptical Properties of Aza[10]helicenes.

The enantioselective synthesis of an aza[10]helicene, possessing two pyridone units, has been achieved by the gold-catalyzed intramolecular quadruple hydroarylation of a tetrayne. This aza[10]helicene was successfully converted into a fully aromatic aza[10]helicene, possessing two pyridine units. Structure-photophysical and chiroptical properties relationship in a series of azahelicene isomers has also been disclosed.

Efficient Synthesis of Cyclic Block Copolymers by Rotaxane Protocol by Linear/Cyclic Topology Transformation.

High-yielding synthesis of cyclic block copolymer (CBC) using the rotaxane protocol by linear-cyclic polymer topology transformation was first demonstrated. Initial complexation of OH-terminated sec-ammonium salt and a crown ether was followed by the successive living ring-opening polymerizations of two lactones to a linear block copolymer having a rotaxane structure by the final capping of the propagation end. CBC was obtained in a high yield by an exploitation of the mechanical linkage through the translational movement of the rotaxane component to transform polymer structure from linear to cyclic.

Reversible polyphenylacetylene helix conversion driven by a thermoresponsive rotaxane switch in the solid state.

The reversible helical pitch change of polyphenylacetylenes by a thermoresponsive rotaxane switch inserted into the side chain was demonstrated through an accompanying color change. Similar to an ethynyl rotaxane monomer, the corresponding polyphenylacetylene having a rotaxane moiety in its side chain exhibited a reversible helical pitch change induced by the thermoresponsive rotaxane switch, i.e.

Effective Approach to Cyclic Polymer from Linear Polymer: Synthesis and Transformation of Macromolecular [1]Rotaxane.

We report a convenient and scalable synthesis of cyclic poly(ε-caprolactone) (PCL) from its linear counterpart based on the rotaxane protocol. Cyclic PCL was prepared by ring-opening polymerization of ε-caprolactone (ε-CL) initiated by a pseudo[2]rotaxane initiator in the presence of diphenylphosphate (DPP) as a catalyst, followed by capping of the propagation end by using a bulky isocyanate to afford macromolecular [2]rotaxane. The successive intramolecular cyclization to macromolecular [1]rotaxane at the polymer terminus proceeded with good yield.

Linear-cyclic polymer structural transformation and its reversible control using a rational rotaxane strategy.

Linear-cyclic polymer structural transformation and its reversibility are demonstrated by a simple but rational strategy using the structural characteristics of crown ether-based rotaxanes. The structure of a polymer containing a [1]rotaxane unit at one end was controlled by conventional protection-deprotection reactions, giving rise to a reversible linear-cyclic polymer structural transformation.

Directed one-pot syntheses of crown ether wheel-containing main chain-type polyrotaxanes with controlled rotaxanation ratios.

The directed synthesis of main chain-type polyrotaxanes possessing crown ether wheels was successfully achieved through two methods, A and B. Method A involved the direct wheel threading of poly(sec-ammonium salt) followed by end-capping with a bulky group, while method B utilized polyaddition of a pseudo[2]rotaxane monomer to facilitate the control of the structure, i.e.

Macromolecular [2]Rotaxanes: Effective Synthesis and Characterization.

Macromolecular [2]rotaxanes, which consist of a polymer chain threading into a wheel component, were synthesized in high yield and with high purity. The synthesis was achieved by the ring-opening polymerization (ROP) of δ-valerolactone (VL) using a hydroxyl-terminated pseudorotaxane as an initiator with diphenyl phosphate as a catalyst in dichloromethane at room temperature. The H NMR, gel permeation chromatography (GPC), and MALDI-TOF-MS measurements of the resulting poly(δ-valerolactone)s clearly indicate the presence of the rotaxane structure with the polymer chain, confirming that the diphenyl phosphate-catalyzed ROP of VL proceeds without deslippage of the wheel component.

Thermoresponsive shuttling of rotaxane containing trichloroacetate ion.

A thermoresponsive rotaxane shuttling system was developed with a trichloroacetate counteranion of an ammonium/crown ether-type rotaxane. Chemoselective thermal decomposition of the ammonium trichloroacetate moiety on the rotaxane yielded the corresponding nonionic rotaxane accompanied by a positional change of the crown ether on the axle. The rotaxane skeleton facilitated effective dissociation of the acid, markedly lowering the thermal decomposition temperature.

Reversible helix-random coil transition of poly(m-phenylenediethynylene) by a rotaxane switch.

Pendant rotaxane switch-tethering poly(m-phenylene diethynylene) was synthesized by the polyoxidative coupling of a rotaxane containing an axle-terminal m-diethynylbenzene group and an optically active crown ether. The reversible helix-random coil transition of the polymer was successfully performed by the positional switching of the rotaxane wheel.

Rational control of a polyacetylene helix by a pendant rotaxane switch.

Polyacetylene bearing a pendant rotaxane moiety with an optically active wheel component was synthesized to realize reversible structural control of its helical structure by position control of the wheel component. Polyacetylene formed a one-handed helical structure only when the optically active wheel component moved close to the main chain.

A rational design for the directed helicity change of polyacetylene using dynamic rotaxane mobility by means of through-space chirality transfer.

Directed helicity control of a polyacetylene dynamic helix was achieved by hybridization with a rotaxane skeleton placed on the side chain. Rotaxane-tethering phenylacetylene monomers were synthesized in good yields by the ester end-capping of pseudorotaxanes that consisted of optically active crown ethers and sec-ammonium salts with an ethynyl benzoic acid. The monomers were polymerized with [{RhCl(nbd)}(2)] (nbd=norbornadiene) to give the corresponding polyacetylenes in high yields.

Neutralization of a sec-ammonium group unusually stabilized by the "rotaxane effect": synthesis, structure, and dynamic nature of a "free" sec-amine/crown ether-type rotaxane.

A fifteen-year riddle has been settled: neutralization, the most popular chemical event, of a crown ether/sec-ammonium salt-type rotaxane has been achieved and a completely nonionic crown ether/sec-amine-type rotaxane isolated. A [2]rotaxane was prepared as a typical substrate from a mixture of dibenzo[24]crown-8 ether (DB24C8) and sec-ammonium hexafluorophosphate (PF(6)) with a terminal hydroxy group through end-capping with 3,5-dimethylbenzoic anhydride in the presence of tributylphosphane as a catalyst in 90% yield. A couple of approaches to the neutralization of the ammonium rotaxane were investigated to isolate the free sec-amine-type rotaxane by decreasing the degree of thermodynamic and kinetic stabilities.

Selective transformation of a crown ether/sec-ammonium salt-type rotaxane to N-alkylated rotaxanes.

Versatile functionalization of a crown ether/sec-ammonium salt-type rotaxane was accomplished. The rotaxane underwent reductive N-alkylation with sodium tri(acyloxy)borohydride or sodium tri(acyloxy)borohydride/arbitrary aldehyde in excellent yields. Structural switching based on reversible tert-ammonium/tert-amine conversion by acid and base was demonstrated as a pH-controlled molecular shuttle.

[Nursing experience in palliative care at the outpatient clinic].

Seven of the 17 patients reported that they were satisfied with the palliative care at our outpatient clinic. A patient's will to stay home, a devoted key person to the patient, procedures such as good pain control and an oral intake were considered to be important factors in palliative care at the outpatient clinic. We should understand that the patient's family attending the outpatient clinic is a part of their important daily life, so we try to make them feel comfortable whenever they come to see us.

Synthesis of [2]rotaxanes by the catalytic reactions of a macrocyclic copper complex.

We synthesized [2]rotaxanes by the reactions catalyzed by a macrocyclic Cu(I)-phenanthroline complex. The catalytic site was located inside the ring component so that the rotaxane could be selectively formed. A C-S bond-forming reaction and oxidative dimerization of alkyne was utilized for the efficient synthesis of a new series of [2]rotaxanes.

Template synthesis of [2]rotaxanes with large ring components and tris(biphenyl)methyl group as the blocking group. The relationship between the ring size and the stability of the rotaxanes.

We synthesized a series of macrocyclic phenanthrolines 3a-e and a tris(biphenyl)methyl derivative 4. [2]Rotaxanes with large ring components (10a,b) were synthesized by the template method, and the stability of the rotaxanes was examined. The study revealed that the tris(biphenyl)methyl group is an effective blocking group for the rotaxanes with up to a 33-membered ring.