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.

The Effect of the Axle End Structure and Number of Through-Space Bonds on the Properties of Rotaxane Crosslinked Polymers.

A rotaxane crosslinker (RC) is known to toughen the resulting rotaxane crosslinked polymer (RCP) via a stress dispersion effect that is attributed to the movable nature of the crosslinking structure. To evaluate this toughening mechanism in detail, a series of structure-definite RCs equipped with different axle end structures or different numbers of wheel components were synthesized, and subjected to free radical polymerization with a vinyl monomer to obtain RCPs. Analyses of the obtained RCPs revealed that the size of the axle end structure should be well-balanced to produce a strong toughening effect, and a [3]rotaxane crosslinker works more effectively than [2]rotaxane to toughen RCPs.

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.

Rotaxanes with dynamic mechanical chirality: Systematic studies on synthesis, enantiomer separation, racemization, and chiral-prochiral interconversion.

Dynamic mechanical chirality of [2]rotaxane consisting of a symmetric wheel and a symmetric axle is discussed the synthesis, enantiomer separation, racemization, and chiral-prochiral interconversion. This [2]rotaxane is achiral and/or prochiral when its wheel locates at the center of the axle, but becomes chiral when the wheel moves from the center of the axle. These were proved by the experiments on the enantiomer separation and racemization.

Topology-transformable block copolymers based on a rotaxane structure: change in bulk properties with same composition.

The topology of polymers affects their characteristic features, i.e., their microscopic structure and macroscopic properties.

An air-stable organometallic polymer containing titanafluorene moieties obtained by the Sonogashira-Hagihara cross-coupling polycondensation.

The synthesis of a polymer containing alternating titanafluorene and arylene ethynylene moieties is described. The polymerization of a 2,7-dibromo-9-titanafluorene derivative with 1,4-dioctyloxy-2,5-diethynylbenzene is carried out at 70 °C for 48 h in tetrahydrofuran (THF) in the presence of palladium dichloride/4,5-bis(diphenylphosphino)-9,9-dimethylxanthene as a catalyst and diisopropylamine as a base to produce a dark red polymer. The polymer thus obtained is soluble in organic solvents and stable towards both air and moisture.

Rotaxane-Based Difunctional Nitrile N-Oxide Crosslinker: Synthesis and Direct Introduction of Movable Crosslinking Points into Ethylene-Propylene-Butadiene Monomer (EPDM) Rubber.

Incorporation of rotaxane scaffolds into the crosslinking points of polymer networks significantly affects their rheological and mechanical properties. The present study involves the synthesis of a new rotaxane-type crosslinker containing nitrile N-oxide functional groups on both the axle and wheel components. The prepared crosslinker is highly reactive; however, it can be isolated and applied in the crosslinking reaction of a commercially important polymer, namely ethylene-propylene-butadiene monomer rubber (EPDM), in the absence of additives and catalysts.

Crystal structure of 2,6-bis-(3-hy-droxy-3-methyl-but-1-yn-1-yl)pyridine monohydrate.

In the title pyridine derivative, CHNO·HO, the two OH groups are oriented in directions opposite to each other with respect to the plane of the pyridine ring. In the crystal, hydrogen bonds between the pyridine mol-ecule and the water mol-ecule, O-H⋯O, O-H⋯O, O-H⋯O and O-H···N, result in the formation of a ribbon-like structure running along [011].

Syntheses of polynorbornadienes by ring-opening metathesis polymerizations of symmetric and non-symmetric 2,3-bis(alkoxycarbonyl)norbornadienes and their conversion to half-ester derivatives.

Libraries of polynorbornadienes were synthesized with good yields with a ruthenium-containing 2nd generation Grubbs catalyst by ring-opening metathesis polymerization (ROMP) of a variety of symmetric and non-symmetric 2,3-bis(alkoxycarbonyl)norbornadiene monomer units prepared from the half-esters obtained efficiently by the selective monohydrolysis reactions of symmetric diesters we reported earlier. Among these polymers, the polynorbornadienes with t-butoxycarbonyl groups derived from non-symmetric monomer units were converted to the half-ester derivatives by deprotection with trifluoroacetic acid, yielding amphiphilic polymers. The hydrogenation reactions of the obtained polymers were carried out to yield polymers having saturated structures in the main chains for improvement of the thermal stabilities.

Macrocyclic Dinuclear Palladium Complex as a Novel Doubly Threaded [3]Rotaxane Scaffold and Its Application as a Rotaxane Cross-Linker.

A dinuclear Pd complex possessing a cyclic ligand was developed as a novel doubly threaded [3]rotaxane scaffold and applied as a rotaxane cross-linker reagent. The dinuclear complex (PdMC) was prepared by one-step macrocyclization followed by the double palladation reaction. H NMR analysis and UV/Vis measurements revealed the formation of a doubly threaded pseudo[3]rotaxane by the complexation of (PdMC) with 2 equivalents of 2,6-disubstituted pyridine 3 through double metal coordination.

Switchable Polymer Materials Controlled by Rotaxane Macromolecular Switches.

The synthesis and dynamic nature of macromolecular systems controlled by rotaxane macromolecular switches are introduced to discuss the significance of rotaxane linking of polymer chains and its topological switching. Macromolecular switches have been synthesized from macromolecular [2]rotaxanes (M2Rs) using -ammonium salt/crown ether couples. The successful synthesis of M2Rs possessing a single polymer axle and one crown ether wheel, constituting a key component of the macromolecular switch, has allowed us to develop various unique applications such as the development of topology-transformable polymers.

Open clamshell dinuclear palladium(ii) complexes possessing out-of-plane anisotropy.

Double cyclometalation of planar, oligomeric phenylpyridines yielded dinuclear palladium(ii) complexes with novel out-of-plane anisotropy. An X-ray crystal structure analysis revealed that the complexes exhibit concave-convex geometry, and 1H NMR measurement evidenced the occurrence of stable out-of-plane anisotropy. The dipole moment and Pd-Pd interaction were investigated by theoretical calculations.

Macrocyclic Metal Complexes Bearing Rigid Polyaromatic Ligands: Synthesis and Catalytic Activity.

We synthesised palladium and platinum complexes possessing cyclic and acyclic pincer-type polyaromatic ligands and investigated their structural effect on the catalysis. The pincer-type bis(6-arylpyridin-2-yl)benzene skeleton was constructed via Kröhnke pyridine synthesis under transition metal-free conditions on gram-scale quantity. Ligand structure significantly influenced catalytic activity toward the platinum-catalysed hydrosilylation of diphenyl acetylenes, despite the ligand-independence of the conformations and electronic properties of these complexes.

Phase Transition Behaviors and Nanoscale Film Morphologies of Poly(δ-valerolactone) Axles Bearing Movable and Fixed Rotaxane Wheels.

In this study, poly(δ-valerolactone) (PVL) axles bearing movable and fixed dibenzo-24-crown-8-ether wheels (rot-M and rot-F) are investigated for the first time in the terms of phase transition and nanoscale film morphology: PVL-rot-M and PVL-rot-F. Interestingly, the PVL axles reveal a strong tendency to form a horizontal lamellar structure with three different rotational crystal lattice domains in nanoscale films. The morphological structural parameters are discernibly varied by the movable and fixed rotaxane wheels.

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.

A Guiding Principle for Strengthening Crosslinked Polymers: Synthesis and Application of Mobility-Controlling Rotaxane Crosslinkers.

Three component mobility controlling vinylic rotaxane crosslinkers with two radically polymerizable vinyl groups (RC_Rs) were synthesized to prove that the mobility of the components of the RC_Rs plays a crucial role in determining the properties of rotaxane-crosslinked polymers (RCPs). RC_Rs (R=H, Me, or Et) were obtained from living ring-opening polymerization. RCP_Et was prepared using RC_Et, which exhibits the lowest component mobility.

Cyclodextrin-Based [3]Rotaxane-Crosslinked Fluorescent Polymer: Synthesis and De-Crosslinking Using Size Complementarity.

Vinyl-group-substituted, α-cyclodextrin-based, size-complementary [3]rotaxanes were synthesized as crosslinkers for rotaxane-crosslinked poly(methyl methacrylate) (RCP) by radical polymerization. The size complementarity of the crosslinkers made it possible to de-crosslink the RCP by heating, and the degree of decoupling was monitored by fluorescence intensity, depending on the state of the axle component of the rotaxane crosslink moiety.

Synthesis of a Structure-Definite α-Cyclodextrin-Based Macromolecular [3]Rotaxane Using a Size-Complementary Method.

The challenging synthesis of an α-cyclodextrin (CD)-based macromolecular rotaxane with definite structure was fulfilled using a size-complementary method. A new peracetylated (PAc) α-CD-based size-complementary [3]rotaxane was prepared and its thermal dissociation kinetics studied. The de-slippage mechanism was found to be different from that of the native α-CD-based system.

Which One is Bulkier: The 3,5-Dimethylphenyl or the 2,6-Dimethylphenyl Group? Development of Size-Complementary Molecular and Macromolecular [2]Rotaxanes.

We developed novel size-complementary molecular and macromolecular rotaxanes using a 2,6-dimethylphenyl terminal group as the axle-end-cap group in dibenzo-24-crown-8-ether (DB24C8)-based rotaxanes, where the 2,6-dimethylphenyl group was found to be less bulky than the 3,5-dimethylphenyl group. A series of molecular and macromolecular [2]rotaxanes that bear a 2,6-dimethylphenyl group as the axle-end-cap were synthesized using unsubstituted and fluorine-substituted DB24C8. Base-induced decomposition into their constituent components confirmed the occurrence of deslipping, which supports the size-complementarity of these rotaxanes.

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.