Defendiendo en las cuatro direcciones: desarrollando los ejercicios de hojoundo del Uechi-ryu para estudiantes avanzados

Este artículo presenta “Defendiendo en las Cuatro Direcciones”, técnicas que añaden un desafío al Uechi-ryu, aunque se hayan incorporado y construido sobre las katas tradicionales que forman los pilares del estilo. Realizar cambios dentro de los métodos de entrenamiento de un estilo simplemente para ser diferente sin ningún otro propósito es de poco valor y realmente destructivo para el sistema. Este artículo describe una aportación realista y llena de significado a la práctica del hojoundo, los ejercicios formales que incorporan movimientos básicos. “Defendiendo en las Cuatro Direcciones” está pensado para estudiantes avanzados que han dominado los fundamentos del Uechi-ryu. Además, la práctica encaja bien para su adaptación y encaje en otros estilos de artes marciales

Effect of core cross-linking on the physical properties of poly(dimethylsiloxane)-based diblock copolymer worms prepared in silicone oil

A trithiocarbonate-capped poly(dimethylsiloxane) (PDMS) precursor is chain-extended via reversible addition–fragmentation chain transfer dispersion polymerization of 2-(dimethylamino)ethyl methacrylate (DMA) in decamethylcyclopentasiloxane (D5) silicone oil at 90 °C. For a fixed mean degree of polymerization (DP) of 66 for the PDMS steric stabilizer block, targeting core-forming PDMA block DPs of between 105 and 190 enables the preparation of either well-defined worms or vesicles at a copolymer concentration of 25% w/w. The as-synthesized linear PDMS66–PDMA100 worms exhibit thermoresponsive behavior in D5, undergoing a worm-to-sphere transition on heating to 100 °C. Variable temperature 1H NMR spectroscopy indicates that this thermal transition is driven by reversible solvent plasticization of the PDMA cores. This change in copolymer morphology is characterized by transmission electron microscopy (TEM) studies, variable temperature dynamic light scattering and small-angle X-ray scattering experiments. Oscillatory rheology studies indicate that degelation occurs at 32 °C, but shear-induced polarized light imaging measurements suggest that full conversion of worms into spheres requires significantly higher temperatures (∼110 °C). 1,2-Bis(2-iodoethoxy)ethane (BIEE) is evaluated as a cross-linker for PDMS66–PDMAx diblock copolymer nano-objects in D5. This bifunctional reagent quaternizes the tertiary amine groups on the DMA residues within the worm cores, introducing cross-links via the Menshutkin reaction. TEM studies confirm that such covalently-stabilized worms no longer undergo a worm-to-sphere transition when heated to 100 °C. Kinetic studies performed on PDMS66–PDMA176 vesicles suggest that cross-linking requires approximately 13 h at 20 °C to ensure that these nano-objects remain intact when dispersed in chloroform, which is a good solvent for both blocks. Oscillatory rheology studies of a PDMS66–PDMA100 worm gel indicated that covalent stabilization using a BIEE/DMA molar ratio of 0.15 increased its dynamic elastic modulus (G′) by almost two orders of magnitude. Furthermore, such cross-linked worms exhibit a much lower critical gelation concentration (∼2% w/w) compared to that of the linear precursor worms (∼12% w/w)

RAFT dispersion polymerization of benzyl methacrylate in silicone oil using a silicone-based methacrylic stabilizer provides convenient access to spheres, worms, and vesicles

Reversible addition–fragmentation chain transfer (RAFT) solution polymerization of 3-[tris(trimethylsiloxy)silyl] propyl methacrylate (SiMA) was conducted in toluene to prepare three PSiMA precursors with mean degrees of polymerization (DP) of 12, 13, or 15. Each precursor was then chain-extended in turn via RAFT dispersion polymerization of benzyl methacrylate (BzMA) in a low-viscosity silicone oil (decamethylcyclopentasiloxane, D5). 1H NMR studies confirmed that such polymerizations were relatively fast, with more than 99% BzMA conversion being achieved within 100 min at 90 °C. Moreover, gel permeation chromatography analysis indicated that these polymerizations were well controlled, with dispersities remaining below 1.25 when targeting PBzMA DPs up to 200. A phase diagram was constructed at a constant copolymer concentration of 20% w/w. Only spherical micelles were accessible when the PSiMA15 stabilizer was utilized, as determined by transmission electron microscopy and small-angle X-ray scattering (SAXS) studies. Nevertheless, these spheres exhibited narrow size distributions and tunable z-average diameters ranging between 19 and 49 nm, as determined by dynamic light scattering. In contrast, spheres, worms, or vesicles could be prepared depending on the target PBzMA DP when utilizing the relatively short PSiMA12 precursor. Moreover, each of these nano-objects could be obtained at copolymer concentrations as low as 5% w/w. To obtain more detailed structural information, these spheres, worms and vesicles were further characterized by SAXS. PSiMA12-PBzMA55 worms formed reasonably transparent free-standing gels when prepared at copolymer concentrations as low as 5% w/w and exhibited an elastic modulus (G′) of 90 Pa at 25 °C, as judged by oscillatory rheology studies. Finally, broadening of the molecular weight distribution was observed during the long-term storage of PSiMA-PBzMA dispersions at ambient temperature. We tentatively suggest that this instability is related to hydroxyl impurities in the SiMA, which leads to cross-linking side reactions. This problem also causes incipient flocculation of the spheres and worms during the long-term storage of such dispersions at 20 °C

RAFT dispersion polymerization of benzyl methacrylate in non-polar media using hydrogenated polybutadiene as a steric stabilizer block

A monohydroxy-capped hydrogenated polybutadiene (PhBD) is converted into a macromolecular chain transfer agent via esterification using a carboxylic acid-functionalized trithiocarbonate. 1H NMR and UV spectroscopy studies indicated a mean degree of esterification of at least 95%. The resulting precursor is used for the reversible addition–fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate (BzMA) in n-dodecane at 90 °C. In principle, systematic variation of the mean degree of polymerization (DP) of the insoluble structure-directing PBzMA block should enable the formation of PhBD–PBzMA spheres, worms or vesicles via polymerization-induced self-assembly (PISA). In practice, only kinetically-trapped spheres are obtained when targeting DPs of up to 300 at 25% w/w solids. However, increasing the copolymer concentration up to 40% or 45% w/w provides access to well-defined worms or vesicles, respectively. Gel permeation chromatography and 1H NMR spectroscopy studies confirmed relatively narrow molecular weight distributions (Mw/Mn < 1.20) and high final BzMA conversions (≥99%), respectively. These diblock copolymer nano-objects were characterized in terms of their particle size and morphology using TEM and DLS and a phase diagram was constructed. According to rheology studies, the free-standing worm gels that are formed at ambient temperature have a critical gelation concentration of approximately 5.0% w/w

Oil-in-oil pickering emulsions stabilized by diblock copolymer nanoparticles

Hypothesis Diblock copolymer nanoparticles have been shown to be Pickering emulsifiers for both oil-in-water and water-in-oil emulsions. Recently, we reported the preparation of sterically-stabilized diblock copolymer spheres in a low-viscosity silicone oil (Macromolecules 53 (2020) 1785–1794). We hypothesized that such spheres could be used as a Pickering emulsifier for a range of oil-in-oil emulsions comprising droplets of a bio-sourced oil dispersed in silicone oil. Experiments Diblock copolymer spheres were prepared via reversible addition-fragmentation chain transfer (RAFT) dispersion polymerization of benzyl methacrylate in silicone oil and characterized by dynamic light scattering and transmission electron microscopy. These spheres were evaluated as Pickering emulsifiers for a series of oil-in-oil Pickering emulsions. The influence of both sphere size and core-forming block composition was investigated. Findings \ud Optimization of the nanoparticle size and core-forming block composition enabled stable bio-sourced oil-in-silicone emulsions to be obtained for nine out of the ten bio-sourced oils investigated. These emulsions were characterized in terms of their mean droplet size by optical microscopy

Synthesis of High χ–Low N Diblock Copolymers by Polymerization-Induced Self-Assembly

Polymerization‐induced self‐assembly (PISA) enables the scalable synthesis of functional block copolymer nanoparticles with various morphologies. Herein we exploit this versatile technique to produce so‐called ‘high χ ‐low N ’ diblock copolymers that undergo nanoscale phase separation in the solid state to produce sub‐10 nm surface features. By varying the degree of polymerization of the stabilizer and core‐forming blocks, PISA provides rapid access to a wide range of diblock copolymers, and enables fundamental thermodynamic parameters to be determined. In addition, the pre‐organization of copolymer chains within sterically‐stabilized nanoparticles that occurs during PISA leads to enhanced phase separation relative to that achieved using solution‐cast molecularly‐dissolved copolymer chains

Polydimethylsiloxane-Based Diblock Copolymer Nano-objects Prepared in Nonpolar Media via RAFT-Mediated Polymerization-Induced Self-Assembly

Monocarbinol-functionalized polydimethylsiloxane (PDMS; mean degree of polymerization = 66) was converted via esterification into a chain transfer agent (CTA) for reversible addition–fragmentation chain transfer (RAFT) polymerization. The degree of esterification was determined to be 94 ± 1% by 1H NMR spectroscopy and 92 ± 1% by UV absorption spectroscopy. This PDMS CTA was then utilized for the dispersion polymerization of benzyl methacrylate (BzMA) in n-heptane at 70 °C. As the PBzMA block grows, it becomes insoluble in the reaction medium, which drives the in situ formation of PDMS–PBzMA diblock copolymer nanoparticles via polymerization-induced self-assembly (PISA). Depending on the precise reaction conditions, the final diblock copolymer chains can self-assemble to form spheres, worms, or vesicles. Systematic variation of the copolymer concentration and the target degree of polymerization (DP) of the PBzMA block enables construction of a phase diagram that allows the reproducible targeting of pure copolymer morphologies, as judged by transmission electron microscopy and dynamic light scattering studies. 1H NMR spectroscopy studies confirm that relatively high BzMA conversions (>90%) can be achieved within 8 h at 70 °C. Gel permeation chromatography studies (THF eluent) indicate high blocking efficiencies and relatively low final polydispersities (Mw/Mn = 1.14–1.34). Small-angle X-ray scattering (SAXS) has been used to characterize selected examples of the spherical nanoparticles in order to obtain volume-average diameters, which increase monotonically when targeting longer DPs for the core-forming PBzMA block. A relatively high copolymer concentration (>25% w/v) is required to obtain a pure worm phase, which occupies an extremely narrow region within the phase diagram. Selected worm and vesicle dispersions were also analyzed by SAXS, which enables determination of the mean worm cross section, mean worm length and vesicle membrane thickness. In addition, the highly anisotropic worms formed free-standing gels in n-heptane, with rheology measurements indicating viscoelastic behavior and a gel storage modulus of around 104 Pa

Bespoke contrast-matched diblock copolymer nanoparticles enable the rational design of highly transparent Pickering double emulsions

We report the preparation of highly transparent oil-in-water Pickering emulsions using contrast-matched organic nanoparticles. This is achieved via addition of judicious amounts of either sucrose or glycerol to an aqueous dispersion of poly(glycerol monomethacrylate)56–poly(2,2,2-trifluoroethyl methacrylate)500 [PGMA–PTFEMA] diblock copolymer nanoparticles prior to high shear homogenization with an equal volume of n-dodecane. The resulting Pickering emulsions comprise polydisperse n-dodecane droplets of 20–100 μm diameter and exhibit up to 96% transmittance across the visible spectrum. In contrast, control experiments using non-contrast-matched poly(glycerol monomethacrylate)56–poly(benzyl methacrylate)300 [PGMA56–PBzMA300] diblock copolymer nanoparticles as a Pickering emulsifier only produced conventional highly turbid emulsions. Thus contrast-matching of the two immiscible phases is a necessary but not sufficient condition for the preparation of highly transparent Pickering emulsions: it is essential to use isorefractive nanoparticles in order to minimize light scattering. Furthermore, highly transparent oil-in-water-in-oil Pickering double emulsions can be obtained by homogenizing the contrast-matched oil-in-water Pickering emulsion prepared using the PGMA56–PTFEMA500 nanoparticles with a contrast-matched dispersion of hydrophobic poly(lauryl methacrylate)39–poly(2,2,2-trifluoroethyl methacrylate)800 [PLMA39–PTFEMA800] diblock copolymer nanoparticles in n-dodecane. Finally, we show that an isorefractive oil-in-water Pickering emulsion enables fluorescence spectroscopy to be used to monitor the transport of water-insoluble small molecules (pyrene and benzophenone) between n-dodecane droplets. Such transport is significantly less efficient than that observed for the equivalent isorefractive surfactant-stabilized emulsion. Conventional turbid emulsions do not enable such a comparison to be made because the intense light scattering leads to substantial spectral attenuation

Small‐angle X‐ray scattering studies of block copolymer nano‐objects: Formation of ordered phases in concentrated solution during polymerization‐induced self‐assembly

We report that polymerization‐induced self‐assembly (PISA) can be used to prepare lyotropic phases comprising diblock copolymer nano‐objects in non‐polar media. RAFT dispersion polymerization of benzyl methacrylate (BzMA) at 90 °C using a trithiocarbonate‐capped hydrogenated polybutadiene (PhBD) steric stabilizer block in n‐dodecane produces either spheres or worms that exhibit long‐range order at 40% w/w solids. NMR studies enable calculation of instantaneous copolymer compositions for each phase during the BzMA polymerization. As the PBzMA chains grow longer when targeting PhBD 80 ‐PBzMA 40 , time‐resolved small‐angle X‐ray scattering reveals intermediate body‐centred cubic (BCC) and hexagonally close‐packed (HCP) sphere phases prior to formation of a final hexagonal cylinder phase (HEX). The HEX phase is lost on serial dilution and the aligned cylinders eventually form disordered flexible worms. The HEX phase undergoes an order‐disorder transition on heating to 150 °C and a pure HCP phase forms on cooling to 20 °C