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Steven P. Armes - One of the best experts on this subject based on the ideXlab platform.

  • RAFT Dispersion Polymerization in Silicone Oil
    Macromolecules, 2019
    Co-Authors: Matthew J. Rymaruk, Saul J. Hunter, Cate T. O'brien, Steven L. Brown, Clive N. Williams, Steven P. Armes
    Abstract:

    A near-monodisperse monohydroxy-terminated polydimethylsiloxane (PDMS; mean degree of Polymerization = 66) was esterified using a carboxylic acid-functionalized trithiocarbonate to yield a PDMS66 precursor with a mean degree of functionality of 92 ± 5% as determined by 1H NMR spectroscopy. This PDMS66 precursor was then chain-extended in turn using eight different methacrylic monomers in a low-viscosity silicone oil (decamethylcyclopentasiloxane, D5). Depending on the monomer type, such syntheses proceeded via either RAFT Dispersion Polymerization or RAFT emulsion Polymerization. In each case the target DP of the core-forming block was fixed at 200, and the copolymer concentration was 25% w/w. Transmission electron microscopy studies indicated that kinetically trapped spheres were obtained in almost all cases. The only exception was 2-(dimethylamino)ethyl methacrylate (DMA), which enabled access to spheres, worms, or vesicles. This striking difference is attributed to the relatively low glass transition temperature for this latter block. A phase diagram was constructed for a series of PDMS66−PDMAx nano-objects by systematically increasing the PDMA target DP from 20 to 220 and varying the copolymer concentration between 10 and 30% w/w. Higher copolymer concentrations were required to access a pure worm phase, while only spheres, vesicles, or mixed phases were accessible at lower copolymer concentrations. Gel permeation chromatography studies indicated a linear evolution of number-average molecular weight (Mn) with PDMA DP while dispersities remained below 1.40, suggesting relatively well-controlled RAFT Polymerizations. Smallangle X-ray scattering (SAXS) was used to characterize selected examples of spheres, worms, and vesicles. PDMS66− PDMA100−112 worms synthesized at 25−30% w/w formed free-standing gels at 20 °C. Oscillatory rheology studies performed on a 30% w/w PDMS66−PDMA105 worm Dispersion indicated a storage modulus (gel strength) of 1057 Pa and a critical gelation concentration (CGC) of approximately 12% w/w. Finally, PDMS66−PDMAx worms could also be prepared in n-dodecane, hexamethyldisiloxane, or octamethylcyclotetrasiloxane. Rotational rheometry studies indicate that such worms are efficient viscosity modifiers for these nonpolar oils.

  • In Situ Spectroscopic Studies of Highly Transparent Nanoparticle Dispersions Enable Assessment of Trithiocarbonate Chain-End Fidelity during RAFT Dispersion Polymerization in Nonpolar Media
    2018
    Co-Authors: Erik J. Cornel, Sandra Van Meurs, Timothy Smith, Paul S. O’hora, Steven P. Armes
    Abstract:

    We report the synthesis of highly transparent poly­(stearyl methacrylate)-poly­(2,2,2-trifluoroethyl methacrylate) (PSMA–PTFEMA) diblock copolymer nanoparticles via Polymerization-induced self-assembly (PISA) in nonpolar media at 70 °C. This was achieved by chain-extending a PSMA precursor block via reversible addition–fragmentation chain transfer (RAFT) Dispersion Polymerization of TFEMA in n-tetradecane. This n-alkane has the same refractive index as the PTFEMA core-forming block at 70 °C, which ensures high light transmittance when targeting 33 nm spherical nanoparticles. Such isorefractivity enables visible absorption spectra to be recorded with minimal light scattering even at 30% w/w solids. However, in situ monitoring of the trithiocarbonate RAFT end-groups during PISA requires selection of a weak n → π* band at 446 nm. Conversion of TFEMA into PTFEMA causes a contraction in the reaction solution volume, leading to an initial increase in absorbance that enables the kinetics of Polymerization to be monitored via dilatometry. At ∼98% TFEMA conversion, this 446 nm band remains constant for 2 h at 70 °C, indicating surprisingly high RAFT chain-end fidelity (and hence pseudoliving character) under monomer-starved conditions. In situ 19F NMR spectroscopy studies provide evidence for (i) the onset of micellar nucleation, (ii) solvation of the nanoparticle cores by TFEMA monomer, and (iii) surface plasticization of the nanoparticle cores by n-tetradecane at 70 °C. Finally, the kinetics of RAFT chain-end removal can be conveniently monitored by in situ visible absorption spectroscopy: addition of excess initiator at 70 °C causes complete discoloration of the Dispersion, with small-angle X-ray scattering studies confirming no change in nanoparticle morphology under these conditions

  • Polymerization induced self assembly of block copolymer nanoparticles via raft non aqueous Dispersion Polymerization
    Progress in Polymer Science, 2016
    Co-Authors: Matthew J Derry, Lee A Fielding, Steven P. Armes
    Abstract:

    There is considerable current interest in Polymerization-induced self-assembly (PISA) via reversible addition–fragmentation chain transfer (RAFT) Polymerization as a versatile and efficient route to various types of block copolymer nano-objects. Many successful PISA syntheses have been conducted in water using either RAFT aqueous Dispersion Polymerization or RAFT aqueous emulsion Polymerization. In contrast, this review article is focused on the growing number of RAFT PISA formulations developed for non-aqueous media. A wide range of monomers have been utilized for both the stabilizer and core-forming blocks to produce diblock copolymer nanoparticles in either polar or non-polar media (including supercritical CO2 and ionic liquids) via RAFT Dispersion Polymerization. Such nanoparticles possess spherical, worm-like or vesicular morphologies, often with controllable size and functionality. Detailed characterization of such sterically stabilized diblock copolymer Dispersions provides important insights into the various morphological transformations that can occur both during the PISA synthesis and also on subsequent exposure to a suitable external stimulus (e.g. temperature).

  • Polymerization induced self assembly of block copolymer nano objects via raft aqueous Dispersion Polymerization
    Journal of the American Chemical Society, 2014
    Co-Authors: Nicholas J Warren, Steven P. Armes
    Abstract:

    In this Perspective, we discuss the recent development of Polymerization-induced self-assembly mediated by reversible addition–fragmentation chain transfer (RAFT) aqueous Dispersion Polymerization. This approach has quickly become a powerful and versatile technique for the synthesis of a wide range of bespoke organic diblock copolymer nano-objects of controllable size, morphology, and surface functionality. Given its potential scalability, such environmentally-friendly formulations are expected to offer many potential applications, such as novel Pickering emulsifiers, efficient microencapsulation vehicles, and sterilizable thermo-responsive hydrogels for the cost-effective long-term storage of mammalian cells.

  • poly methacrylic acid based ab and abc block copolymer nano objects prepared via raft alcoholic Dispersion Polymerization
    Polymer Chemistry, 2014
    Co-Authors: Mona Semsarilar, Adam Blanazs, Vincent Ladmiral, Steven P. Armes
    Abstract:

    A series of well-defined amphiphilic poly(methacrylic acid)–poly(benzyl methacrylate) (PMAA–PBzMA) diblock copolymers are synthesized via Polymerization-induced self-assembly using an alcoholic Dispersion Polymerization formulation. Chain growth is mediated via reversible addition–fragmentation chain transfer Polymerization (RAFT) chemistry using a trithiocarbonate-based chain transfer agent (CTA) at 70 °C. The poly(methacrylic acid) block is soluble in ethanol and acts as a steric stabilizer for the growing insoluble PBzMA chains, resulting in the in situ generation of diblock copolymer nano-objects in the form of spheres, worms or vesicles, depending on the precise reaction conditions. Copolymer morphologies can be covalently stabilized via cross-linking to prevent their dissociation when transferred into aqueous solution, which leads to the formation of highly anionic nano-objects due to ionization of the PMAA stabilizer chains. ABC triblock copolymer nanoparticles can also be prepared using this approach, where the third block is based on the semi-fluorinated monomer, 2,2,2-trifluoroethyl methacrylate (TFEMA). GPC studies confirm that chain extension is efficient and high TFEMA conversions can be achieved. Microphase separation between the mutually incompatible PBzMA and semi-fluorinated PTFEMA core-forming blocks occurs, producing a range of remarkably complex semi-fluorinated triblock copolymer morphologies.

Masayoshi Okubo - One of the best experts on this subject based on the ideXlab platform.

Patrick Lacroixdesmazes - One of the best experts on this subject based on the ideXlab platform.

Alexander J C Kuehne - One of the best experts on this subject based on the ideXlab platform.

Zhaohua Zeng - One of the best experts on this subject based on the ideXlab platform.

  • z type and r type macro raft agents in raft Dispersion Polymerization another mechanism perspective on pisa
    Polymer Chemistry, 2016
    Co-Authors: Jianbo Tan, Jianwen Yang, Zhaohua Zeng
    Abstract:

    In a common RAFT Dispersion Polymerization induced self-assembly (PISA) formulation, R-type macro-RAFT agents with a solvophilic chain attached at the leaving group side are normally used to mediate the Polymerization, meanwhile Z-type macro-RAFT agents with a solvophilic chain attached at the Z-group side are seldom employed. In this paper, we have tried to use a Z-type macro-RAFT agent (mPEG113-BTPA) to mediate RAFT Dispersion Polymerization of styrene, and found that the process exhibited a poorer PISA tendency and weaker molecular weight control. In comparison, we have conducted the same process mediated with an R-type macro-RAFT agent (mPEG113-DDMAT), and found that the formulation exhibited a typical PISA process, and nanoparticles were produced in situ. Further experiments suggest that the location of RAFT groups plays a key role for the PISA process in RAFT Dispersion Polymerization. The RAFT groups will be embedded in the produced particles when an R-type macro-RAFT agent is employed, but locate on the particle surface in the case of the Z-type macro-RAFT agent. We have tried to employ the RAFT groups on the surface of the mPEG113-BTPA stabilized particles to modify the particle surface, and successfully removed the solvophilic block via breaking the RAFT group, and generated the poly(dimethylacrylamide) block by surface-initiated RAFT Polymerization. Based on the above mechanism perspective, we have designed a preliminary experiment, and found that well-defined monodisperse nanospheres could be prepared by heterogeneous RAFT Dispersion Polymerization mediated with a Z-type macro-RAFT agent-based block copolymer which was synthesized via pre-Polymerization of styrene in 1,4-dioxane mediated with mPEG113-BTPA.

  • PMMA Microspheres with Embedded Lanthanide Nanoparticles by Photoinitiated Dispersion Polymerization with a Carboxy-Functional Macro-RAFT Agent
    2015
    Co-Authors: Jianbo Tan, Guangyao Zhao, Zhaohua Zeng, Mitchell A. Winnik
    Abstract:

    Functional poly­(methyl methacrylate) (PMMA) microbeads with a very narrow size distribution were synthesized by photoinitiated RAFT Dispersion Polymerization in aqueous ethanol using an acrylic acid–oligo­(ethylene glycol) copolymer as a macro-RAFT agent. These particles are a prototype for multiparameter bead-based assays employing mass cytometry, a technique in which metal-encoded beads are injected into the plasma torch of an inductively coupled plasma mass spectrometer (ICP-MS), and the metal ions generated are detected by time-of-flight mass spectrometry. To label the beads, the Polymerization reaction was carried out in the presence of various types of small (ca. 5 nm) lanthanide fluoride (LnF3) nanoparticles (e.g., LaF3, CeF3, and TbF3) with polymerizable methacrylate groups on their surface. The type of metal ion and the metal content of the PMMA microbeads could be varied by changing the composition of the reaction medium. An important feature of these microbeads is that acrylic acid groups in the corona are available for covalent attachment of biomolecules. As a proof of concept, FITC–streptavidin (FITC-SAv) was covalently coupled to the surface of a Ln-encoded microbead sample. The number of FITC-SAv binding sites on the beads was determined through three parallel assays involving biotin derivatives. Interaction of the beads with a biotin–tetramethylrhodamine derivative was monitored by fluorescence, whereas interaction of the beads with a biotin-DOTA-Lu derivative was monitored both by ICP-MS and by mass cytometry. Each measurement detected an average of ca. 5 × 104 biotins per microsphere. Control experiments with beads covalently labeled with FITC–bovine serum albumin (FITC-BSA) showed only very low levels of nonspecific binding

  • synthesis of pmma microparticles with a narrow size distribution by photoinitiated raft Dispersion Polymerization with a macromonomer as the stabilizer
    Macromolecules, 2014
    Co-Authors: Jianbo Tan, Guangyao Zhao, Zhaohua Zeng, Mitchell A. Winnik
    Abstract:

    Macromonomers can serve as efficient and effective stabilizers for Dispersion Polymerization of monomers such as styrene and methyl methacrylate, but the size distributions of the polymer microparticles obtained tend to be broad. We are interested in functional microbeads which can be used for immunoassays, where the size distribution has to be very narrow. We report a photoinitiated RAFT Dispersion Polymerization of methyl methacrylate (MMA) in ethanol–water mixtures, with methoxy-poly(ethylene glycol) methacrylate (Mn = 2000 g/mol, EO45) as the reactive steric stabilizer. We identify reaction conditions where one can obtain PMMA microspheres with coefficient of variation in the particle diameter (CVd) less than 3%. Carboxy-functional PMMA microspheres were obtained by a two-stage (seeded) Polymerization with methacrylic acid (MAA) added as a comonomer in the second stage. We show that the functional microspheres prepared in this way are effective substrates for the covalent attachment of proteins such a...

  • photoinitiated raft Dispersion Polymerization a straightforward approach toward highly monodisperse functional microspheres
    Macromolecules, 2012
    Co-Authors: Jianbo Tan, Xin Rao, Hancheng Deng, Jianwen Yang, Zhaohua Zeng
    Abstract:

    A straightforward Dispersion Polymerization procedure for the synthesis of monodisperse functional polymeric microspheres is proposed in this article. This method overcomes the problems deriving from the highly sensitive nucleation stage by introducing both photoinitiation and a RAFT chain transfer agent to the reaction. The process of the formation and growth of particles in the procedure was investigated and found to be quite different from that in a traditional Dispersion Polymerization. Various kinds of PMMA-based functional microspheres with high size uniformity were synthesized in a single step by this strategy. The microspheres remained uniform in size, even at concentrations of cross-linker or functional comonomer up to 10 wt %.