Effect of scandium triflate on the RAFT copolymerization of methyl acrylate and vinyl acetate controlled by an acid/base “switchable” chain transfer agent

Modulation of the activity of an acid/base switchable dithiocarbamate RAFT agent, cyanomethyl (4-fluorophenyl)(pyridin-4-yl)carbamodithioate, with the Lewis acid scandium triflate (Sc(OTf)3) was investigated to examine the ability to deliver improved control over RAFT copolymerizations involving both more-activated and less-activated monomers—specifically the copolymerization of methyl acrylate (MA) and vinyl acetate (VAc). The introduction of either 0.5 or 1 mol equiv of Sc(OTf)3, with respect to RAFT agent, into a RAFT copolymerization of MA and VAc provides substantially improved control resulting in significantly reduced molar mass dispersities (Đ) (∼1.1–1.3) than achieved in its absence (Đ ∼ 1.3–1.4). Furthermore, similar introduction of Sc(OTf)3 into MA homopolymerization mediated by the same RAFT agent also delivered polymers of very low Đ (∼1.15). Sc(OTf)3 was also found to lower the rate of polymerization and alter the copolymerization reactivity ratios for MA and VAc. Increasing the Lewis acid concentration provides enhanced incorporation of the less active monomer, VAc, into the copolymers ([Sc(OTf)3]/[RAFT] = 0, rMA = 4.04, rVAc = 0.032; [Sc(OTf)3]/[RAFT] = 0.5, rMA = 3.08, rVAc = 0.17; [Sc(OTf)3]/[RAFT] = 1, rMA = 2.68, rVAc = 0.62). Carbon nuclear magnetic resonance (13C NMR) and differential scanning calorimetry (DSC) analysis of preparative samples confirm the enhanced VAc incorporation with increased levels of Sc(OTf)3. Importantly the inclusion of Sc(OTf)3 does not deleteriously affect the thiocarbonylthio end-groups of the RAFT polymers, with high end-group fidelity being observed in all copolymerizations

FRONTAL PLANE KNEE MOTION OF ACL-REPAIRED AND NON-INJURED FEMALES WHEN USING KNEE SAVERS

Women are four to six times more likely to sustain ACL injuries compared to male counterparts. Few investigations have explored if ergonomic devices may alleviate the stress placed on the ACL during deep squatting. The purpose of the study was to determine if Knee Savers® (KS) influenced the frontal plane knee motion when previously-injured and healthy participants completed a squat. Female participants (ACLrepaired: n=10; healthy: n=10) completed a deep squat with and without KS using 2-D videography methods. Results indicated a greater medial motion of the patella in the frontal plane in the right leg of non-injured participants when compared to the ACLrepaired group (p = 0.04). When squatting with KS, the non-injured group experienced more frontal plane motion at the knee, compared to the ACL-repaired group

The reactivity of N-vinylcarbazole in RAFT polymerization: trithiocarbonates deliver optimal control for the synthesis of homopolymers and block copolymers

This is an accepted manuscript of an article published by Royal Society of Chemistry in Polymer Chemistry on 30/04/2012, available online: https://doi.org/10.1039/C3PY00487B The accepted version of the publication may differ from the final published version.The use of various RAFT agents (ZC(S)SR) including dithiobenzoates (Z = Ph), trithiocarbonates (Z = SR′), xanthates (Z = OR′), and conventional and switchable N-aryldithiocarbamates (Z = NR′Ar) in RAFT polymerization of N-vinylcarbazole (NVC) has been explored with a view to establishing which is most effective. Consistent with earlier work, we find that xanthates and N-aryldithiocarbamates give adequate control (dispersities < 1.3) while dithiobenzoates give marked retardation. However, contrary to popular belief, we find that the polymerization of NVC is best controlled with trithiocarbonate RAFT agents, which provide both good molecular weight control, very narrow dispersities (1.1), and high end-group fidelity. The results demonstrate that NVC has intermediate reactivity, i.e. between that of the traditional more activated (MAMs; styrene, acrylates) and less activated monomers (LAMs; vinyl acetate, N-vinylpyrrolidone). A further key to good control is the selection of RAFT agent R substituent to be both a good leaving group and a good initiating radical. The cyanomethyl group meets these criteria whereas phenylethyl is a poor initiating radical for NVC polymerization. A further demonstration of the intermediate reactivity of NVC and the derived propagating radical was the successful preparation of both poly(n-butyl acrylate)-block-poly(N-vinylcarbazole) and poly(N-vinylcarbazole)-block-poly(n- butyl acrylate) with a trithiocarbonate RAFT agent (the sequence of block synthesis is not important). Two-dimensional, liquid chromatography near critical conditions-gel permeation chromatography (LCCC-GPC) has been applied to demonstrate block purity. The corresponding styrene-based blocks can also be successfully synthesized, however, the reinitiation of NVC polymerization by the polystyryl radical proved to be a constraint on the purity of polystyrene-block-poly(N-vinylcarbazole). © 2013 The Royal Society of Chemistry.The authors gratefully acknowledge the Capability Development Fund of CSIRO Materials Science and Engineering for financial support. D.J.K. acknowledges the Office of the Chief Executive of CSIRO for an OCE postdoctoral fellowship and the School of Science and Technology at the University of New England for a start-up grant.Published versio

Synthesis and characterization of polystyrene-blockpoly(vinylbenzoic acid): a promising compound for manipulating photoresponsive properties at the nanoscale

"Published online: 27 January 2015"Using reversible addition-fragmentation chain transfer (RAFT) polymerization, the effect of PSt macroRAFT and 4VBA ratio on the synthesis of a carboxylic acid functional block copolymer (PSt-b-P4VBA) was studied. PSt macroRAFT polymer was initially prepared followed by the insertion of 4-vinylbenzoic acid (4VBA) monomer. The chemical structure of the diblock copolymer was confirmed by NMR and FTIR. The effect of PSt macroRAFT and 4VBA ratio on copolymerization yield and on molecular weight distribution was assessed by gel permeation chromatography. The rate of polymerization did not change as the 4VBA/PSt macroRAFT ratio increased, indicating an ideal amount of 4VBA insertion. An optimal ratio of [PSt macroRAFT]:[AIBN]:[4VBA] was 1.2:1:180. DSC and XRD confirmed the amorphous structure of homo and copolymer. Thermal stability was higher for PSt-b-P4VBA forming activated porous carbon char by dehydration, carbonization and oxidation. SEM and STEM observations showed a morphological evolution between PSt macroRAFT and the correspondent copolymer.The authors acknowledge the n-STeP-Nanostructured systems for Tailored Performance, with reference NORTE-07-0124-FEDER-000039, supported by the Programa Operacional Regional do Norte (ON.2), PEst-C/CTM/LA0025/2013 (Strategic Project-LA 25-2013-2014)

The effect of Z-group modification on the RAFT polymerization of N-vinylpyrrolidone controlled by "switchable" N-pyridyl-functional dithiocarbamates

This is an accepted manuscript of an article published by Royal Society of Chemistry in the Polymer Chemistry on 24/08/2015, available online: https://doi.org/10.1039/C5PY01021G The accepted version of the publication may differ from the final published version.The ability of a RAFT agent to control the polymerization of a monomer is dictated by the structures of both the monomer and the RAFT agent. In this paper, the polymerization of N-vinylpyrrolidone was examined with a series of cyanomethyl N-aryl-N-pyridyldithiocarbamates [(4-R′Ph)N(py)C(S)SCH2CN] varying in the substituent (R′) at the 4-position on the phenyl ring. The polymerization of N-vinylpyrrolidone was best controlled when R′ was methoxy; one of the least active RAFT agents in the series. The preservation of RAFT agent functionality was demonstrated by chain extension experiments with further N-vinylpyrrolidone. Again best control again was found for the RAFT agent with R′ = MeOPh. The utility of this RAFT agent was also proved with the preparation of poly(N-isopropylacrylamide)-block-poly(N-vinylpyrrolidone).The authors gratefully acknowledge the Australian Government for award of an Australian Postgraduate Award to S.J.S., the CSIRO Manufacturing Flagship and the School of Science and Technology at the University of New England for project funding.Published versio

A Rheometry Method to Assess The Evaporation-Induced Mechanical Strength Development of Polymer Solutions Used For Membrane Applications

Rotational and oscillatory shear rheometry were used to quantify the flow behavior under minimal and significant solvent evaporation conditions for polymer solutions used to fabricate isoporous asymmetric membranes by the self-assembly and non-solvent induced phase separation (SNIPS) method. Three different A-B-C triblock terpolymer chemistries of similar molar mass were evaluated: polyisoprene-^-polystyrene-6-poly(4-vinylpyridine) (ISV); polyisoprene-6- polystyrene-6-poly(V,A-dimethylacrylamide) (ISD); and polyisoprene-Z\u3e-polystyrene-h-poly(fer/- butyl methacrylate) (ISB). Solvent evaporation resulted in the formation of a viscoelastic film typical of asymmetric membranes. Solution viscosity and film viscoelasticity were strongly dependent on the chemical structure of the triblock terpolymer molecules. A hierarchical magnitude (ISV\u3eISB\u3eISD) was observed for both properties, with ISV solutions displaying the greatest solution viscosity, fastest film strength development, and greatest strength magnitude

Review of the Palaearctic species of Ismaridae Thomson, 1858 (Hymenoptera: Diaprioidea)

This is an open access article, available to all readers online, published under a Creative Commons BY-NC-ND license: https://creativecommons.org/licenses/by-nc-nd/3.0/. The attached file is the published version of the article

Bespoke cationic nano-objects via RAFT aqueous dispersion polymerisation

A range of cationic diblock copolymer nanoparticles are synthesised via polymerisation-induced self-assembly (PISA) using a RAFT aqueous dispersion polymerisation formulation. The cationic character of these nanoparticles can be systematically varied by utilising a binary mixture of two macro-CTAs, namely non-ionic poly(glycerol monomethacrylate) (PGMA) and cationic poly[2-(methacryloyloxy)ethyl]trimethylammonium chloride (PQDMA), with poly(2-hydroxypropyl methacrylate) (PHPMA) being selected as the hydrophobic core-forming block. Thus a series of cationic diblock copolymer nano-objects with the general formula ([1 - n] PGMAx + [n] PQDMAy) - PHPMAz were prepared at 20% w/w solids, where n is the mol fraction of the cationic block and x, y and z are the mean degrees of polymerisation of the non-ionic, cationic and hydrophobic blocks, respectively. These cationic diblock copolymer nanoparticles were analysed in terms of their chemical composition, particle size, morphology and cationic character using 1H NMR spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), and aqueous electrophoresis, respectively. Systematic variation of the above PISA formulation enabled the formation of spheres, worms or vesicles that remain cationic over a wide pH range. However, increasing the cationic character favors the formation of kinetically-trapped spheres, since it leads to more effective steric stabilisation which prevents sphere-sphere fusion. Furthermore, cationic worms form a soft free-standing gel at 25 °C that undergoes reversible degelation on cooling, as indicated by variable temperature oscillatory rheology studies. Finally, the antimicrobial activity of this thermo-responsive cationic worm gel towards the well-known pathogen Staphylococcus aureus is examined via direct contact assays