Ab initio RAFT emulsion polymerization mediated by small cationic RAFT agents to form polymers with low molar mass dispersity

We report on low molar mass cationic RAFT agents that provide predictable molar mass and low molar mass dispersities (Đm) in ab initio emulsion polymerization. Thus RAFT emulsion polymerization of styrene in the presence of the protonated RAFT agent, ((((cyanomethyl)thio)carbonothioyl)(methyl)amino)pyridin-1-ium toluenesulfonate (4), and the analogous methyl-quaternized RAFT agents, 4-((((cyanomethyl)thio)carbonothioyl)(methyl)amino)-1-methylpyridin-1-ium dodecyl sulfate (6), provide low dispersity polystyrene with Đm 1.2–1.4 for Mn ∼ 20 000. We postulate that the success of ab initio emulsion polymerization with 4 is due to the hydrophilicity of the pyridinium group, which is such that the water soluble RAFT agent partitions predominantly into the aqueous phase under the conditions of the experiment and that 4 provides little retardation. With 6, when the counterion is dodecyl sulfate, we can achieve “surfactant-free” RAFT emulsion polymerization to provide a low Đm polystyrene. However, the RAFT end-group is lost on isolation of the polymer. Preliminary results show that this class of RAFT agent is broadly applicable in ab initio emulsion polymerization of other more-activated monomers (e.g., butyl acrylate, butyl methacrylate). Furthermore, cyanomethyl(pyridin-4-yl)carbamodithioate (3, the RAFT agent in neutral form) provides molar mass control and Đm < 1.8 in ab initio emulsion polymerization of less activated monomers, specifically, the vinyl esters, vinyl acetate and vinyl benzoate.Published onlin

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

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

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(Nvinylpyrrolidone)

Effect of the Z- and Macro‐R‐Group on the Thermal Desulfurization of Polymers Synthesized with Acid/Base "Switchable" Dithiocarbamate RAFT Agents

Thermolysis is examined as a method for complete desulfurization of reversible addition‐fragmentation chain transfer (RAFT)‐synthesized polymers prepared with acid/base "switchable" N‐methyl‐N‐pyridyldithiocarbamates [R—S2CZ or R—S2CZH+]. Macro‐RAFT agents from more activated monomers (MAMs) (i.e., styrene (St), N‐isopropylacrylamide (NIPAm), and methyl methacrylate (MMA)) with R—S2CZH+ and less activated monomers (LAMs) (i.e., vinyl acetate (VAc) and N‐vinylpyrolidone (NVP)) with R—S2CZ are prepared by RAFT polymerization and analyzed by thermogravimetric analysis. In all cases, a mass loss consistent with loss of the end group (Z—CS2H) is observed at temperatures lower than, and largely discrete from, that required for further degradation of the polymer. The temperatures for end group loss and the new end groups formed are strongly dependent on the identity of the R—(P)n and the state of the pyridyl Z group; increasing in the series poly(MMA) 2CZ and poly(MMA) 2CZH+. Clean end group removal is possible for poly(St) and poly(NVP). For poly(NIPAm), the thiocarbonyl chain end is removed, but the end group identity is less certain. For poly(MMA) and poly(VAc), some degradation of the polymer accompanies end group loss under the conditions used and further refinement of the process is required

Electrospun scaffold micro-architecture induces an activated transcriptional phenotype within tendon fibroblasts

Biomaterial augmentation of surgically repaired rotator cuff tendon tears aims to improve the high failure rates (∼40%) of traditional repairs. Biomaterials that can alter cellular phenotypes through the provision of microscale topographical cues are now under development. We aimed to systematically evaluate the effect of topographic architecture on the cellular phenotype of fibroblasts from healthy and diseased tendons. Electrospun polydioxanone scaffolds with fiber diameters ranging from 300 to 4000 nm, in either a highly aligned or random configuration, were produced. Healthy tendon fibroblasts cultured for 7 days on scaffolds with highly aligned fibers demonstrated a distinctive elongated morphology, whilst those cultured on randomly configured fibers demonstrated a flattened and spread morphology. The effect of scaffold micro-architecture on the transcriptome of both healthy and diseased tendon fibroblasts was assessed with bulk RNA-seq. Both healthy (n = 3) and diseased tendon cells (n = 3) demonstrated a similar transcriptional response to architectural variants. Gene set enrichment analysis revealed that large diameter (≥2000 nm) aligned scaffolds induced an upregulation of genes involved in cellular replication and a downregulation of genes defining inflammatory responses and cell adhesion. Similarly, PDPN and CD248, markers of inflammatory or “activated” fibroblasts, were downregulated during culture of both healthy and diseased fibroblasts on aligned scaffolds with large (≥2000 nm) fiber diameters. In conclusion scaffold architectures resembling that of disordered type III collagen, typically present during the earlier phases of wound healing, resulted in tendon fibroblast activation. Conversely, scaffolds mimicking aligned diameter collagen I fibrils, present during tissue remodelling, did not activate tendon derived fibroblasts. This has implications for the design of scaffolds used during rotator cuff repair augmentation

Easy Resources for Managing Your Ocean Data

What are the top things data curators wish scientists with deep ocean data were aware of? Where can you start learning how to do a bit better with managing your data, so it is useful for addressing big science and policy questions about the deep sea and preserved for future use? DOOS, in collaboration with the ESIP Marine Data Cluster,  has pulled together a set of guidance for data management. We know you are busy, so we've kept it to a few essential, entry-level pointers. Click on the links embedded in the PDF, or go to the companion web page to see the links listed out. We thank ESIP and the DOOS NSF award for supporting this work.   </p