Hyerbranched polydendrons: a new macromolecular architecture

A novel architecture ‘hyperbranched polydendrons’ (hyp-polydendrons) was produced via the synthesis of low generation dendron initiators for ATRP and subsequent copolymerisation of vinyl and divinyl monomers, to give large polymeric macromolecules containing dendron moieties at the end of each primary chain. Subsequent studies of such materials were performed to assess their ability to form nanoparticles via a nanoprecipitation approach, utilising organic solvent and aqueous nanoparticle formation. It was found that the branched polymers were superior to the linear polymer analogues when assessing their nanoprecipitation behaviour. Mixed initiator hyp-polydendrons were also synthesised by the statistical incorporation of different functionality initiators into the reaction mixture. Here a G2 dendron and different PEG macroinitiators were mixed statistically to produce a series of materials where the primary chain length of the monomer HPMA was also varied. This led to a series of nanoparticles which showed a variation of internal environments when studied using different fluorescent dyes (Nile red and pyrene). Initial pharmacological experiments were promising, however, the initial set of materials did not show prolonged stability in physiologically relevant conditions when using a short PEG macroinitiator (750PEG). Extending the length of the PEG chain (2000PEG initiator) in the mixed polymerisations produced a range of materials with varying solubilities and, therefore, nanoprecipitation behaviour. Nanoparticles were formed which were stable under physiologically relevant conditions and were studied for their cytotoxicity and transcellular permeability in Caco- 2 cells. These materials showed limited toxicity at the concentrations studied and enhanced permeation though the Caco-2 cell monolayer, which is a model of the intestinal epithelial cells. Further studies of the nanoprecipitation behaviour of different molecular weight fractions of the hyp-polydendrons were conducted. This involved separation of molecular weight fractions by dialysis of the hyp-polydendrons against two different good solvents, leading to two HMW fractions and two LMW fractions. Analysis of the nanoprecipitation behaviour of these fractions showed that the HMW fractions produced particles with more narrow PdIs, and the mixing of a low amount of a HMW fraction (1 wt%) with a linear polymer improved the nanoprecipitation behaviour hugely. Encapsulation of two different guest molecules via nanoprecipitation was assessed using FRET, which can report on the proximity of two fluorophores. Dual loading of the particles with DiO and DiI in a 1:1 ratio gave particles which exhibited a FRET signal, therefore indicating that the two fluorophores were located in the same nanoparticle. Somewhat unexpectedly it was found that upon mixing of the two singly loaded particles the observed FRET ratio increased over time until it reached a similar value obtained within the dual loaded nanoparticles. This was possibly due to nanoparticle-nanoparticle collisions. Therefore hyp-polydendrons were produced and utilised to form nanoparticles via a nanoprecipitation approach. Loading of the nanoparticles was achieved and pharmacological benefits were observed for some of the nanoparticle samples, suggesting future benefits for these polymer architectures in nanomedicine applications

Synthesis of well-defined epoxy-functional spherical nanoparticles by RAFT aqueous emulsion polymerization

The environmentally-friendly synthesis of epoxy-functional spherical nanoparticles has been achieved using polymerization-induced self-assembly (PISA) in aqueous solution. Firstly, a non-ionic hydrophilic stabilizer block, poly(glycerol monomethacrylate) (PGMA), was prepared by reversible addition–fragmentation chain transfer (RAFT) solution polymerization in ethanol. This water-soluble precursor was subsequently chain-extended via RAFT aqueous emulsion polymerization of glycidyl methacrylate (GlyMA) at 50 °C and neutral pH to ensure maximum retention of the epoxy functionality. PISA leads to the formation of well-defined PGMA-PGlyMA spherical diblock copolymer nanoparticles at up to 35% w/w solids and 1H NMR spectroscopy studies indicated that virtually all of the epoxy groups survive such relatively mild conditions. DMF GPC studies confirmed that relatively low dispersities (Mw/Mn </p

Long-Term Stability of n-Alkane-in-Water Pickering Nanoemulsions: Effect of Aqueous Solubility of Droplet Phase on Ostwald Ripening

High-pressure microfluidization is used to prepare a series of oil-in-water Pickering nanoemulsions using sterically-stabilized diblock copolymer nanoparticles as the Pickering emulsifier. The droplet phase comprised either n-octane, n-decane, n-dodecane, or n-tetradecane. This series of oils enabled the effect of aqueous solubility on Ostwald ripening to be studied, which is the primary instability mechanism for such nanoemulsions. Analytical centrifugation (LUMiSizer instrument) was used to evaluate the long-term stability of these Pickering nanoemulsions over time scales of weeks/months. This technique enables convenient quantification of the fraction of growing oil droplets and confirmed that using n-octane (aqueous solubility = 0.66 mg dm–3 at 20 °C) leads to instability even over relatively short time periods. However, using n-tetradecane (aqueous solubility = 0.386 μg dm–3 at 20 °C) leads to significantly improved long-term stability with respect to Ostwald ripening, with all droplets remaining below 1 μm diameter after 6 weeks storage at 20 °C. In the case of n-dodecane, the long-term stability of these new copolymer-stabilized Pickering nanoemulsions is significantly better than the silica-stabilized Pickering nanoemulsions reported in the literature by Persson et al. (Colloids Surf., A,2014,459, 48–57). This is attributed to a much greater interfacial yield stress for the former system, as recently described in the literature (see P. J. Betramo et al. Proc. Natl. Acad. Sci. U.S.A.,2017,114, 10373–10378)

Role of highly branched, high molecular weight polymer structures in directing uniform polymer particle formation during nanoprecipitation

The new macromolecular architecture, hyperbranched polydendrons, are composed of a broad distribution of molecular weights and architectural variation; however, nanoprecipitation of these materials yields highly uniform, dendron-functional nanoparticles. By isolating different fractions of the diverse samples, the key role of the most highly branched structures in directing nucleation and growth has been explored and determined.</div

Hyperbranched polydendrons: a new controlled macromolecular architecture with self-assembly in water and organic solvents

A new macromolecular architecture (hyperbranched polydendrons) is presented. Combining aspects of linear-dendritic hybrids, controlled radical polymerisation and branched vinyl polymerisation, the materials have very high molecular weight (Mw > 1 MDa) and surface functionality. Although dispersities are broad (Đ up to 25) the structures behave with remarkable uniformity upon manipulation of solvent environment. Comparisons of conventional linear-dendritic hybrids and hyperbranched polydendrons are presented, including aspects of their synthesis. Under solvent exchange in organic media, a reversible self-assembly to form monodispersed nanoparticles (PDI as low as 0.013) is observed. Self-assembly and encapsulation is also observed during aqueous nanoprecipitation of the hyperbranched materials, with nanoparticle size (diameters from 60–140 nm) controlled through modification of precipitation conditions and the generation of the ideally branched dendrons at one end of each primary chain. The aqueous nanoparticles are highly stable and offer considerable opportunities for tailored functionality and future advanced applications.</div

The Environmental Context and Function of Burnt-Mounds : New Studies of Irish Fulachtaí Fiadh

The authors acknowledge funding from The Leverhulme Trust (F/00144/AI) and assistance from a large number of individuals including; Margaret Gowen (access to sites and assistance throughout),A. Ames, H, Essex (pollen processing), S. Rouillard & R. Smith (illustrations), C. McDermott, S. Bergerbrandt, all the staff of Margaret Gowen & Co. Ltd, TVAS Ireland and CRDS. Excavation works and some post-excavation analysis was paid for my Bord Gáis and the National Roads Authority (now Transport Infrastructure Ireland). Thanks also to David Smith for access to the Maureen Girling collection and assistance with identifications.Peer reviewedPostprintPostprin

Soft and rigid core latex nanoparticles prepared by RAFT-mediated surfactant-free emulsion polymerization for cellulose modification – a comparative study

Latex nanoparticles comprising cationically charged coronas and hydrophobic cores with different glass transition temperatures (Tg) have been prepared by surfactant-free, RAFT-mediated emulsion polymerization, where the particles form through a polymerization-induced self-assembly (PISA) type mechanism. Poly(2-dimethylaminoethyl methacrylate-co-methacrylic acid) (P(DMAEMA-co-MAA)) was utilized as a hydrophilic macroRAFT agent for the polymerization of methyl methacrylate (MMA) or n-butyl methacrylate (nBMA), respectively, resulting in two different latexes, with either a core of high (PMMA) or low (PnBMA) Tg polymer. By varying the molar mass of the hydrophobic block, latexes of different sizes were obtained (DHca. 40–120 nm). The adsorption of the latexes to cellulose model surfaces and cellulose nanofibrils (CNF) was studied using quartz crystal microbalance with dissipation monitoring (QCM-D). The surfaces with adsorbed PnBMA latexes yielded hydrophobic surfaces both before and after annealing, whereas surfaces with adsorbed PMMA latex became hydrophobic only after annealing, clearly showing the influence of the Tg of the core. The latexes were also used to modify macroscopic cellulose in the form of filter papers. Similar to the CNF surfaces, no annealing was required to achieve hydrophobic surfaces with PnBMA latexes. Finally, nanocomposites of CNF and the polymer nanoparticles were prepared through a one-pot mixing procedure. It was found that the largest synthesized PMMA latex (120 nm) facilitated a more strainable CNF network at 50% relative humidity, with a nearly 200% increase in strain at break compared to the neat CNF reference film as well as to the composite films with PnBMA latexes or to the smaller sized PMMA latexes. This difference was attributed to the spherical shape and rigidity of the large PMMA latex nanoparticles during composite formation. This highly interesting result should indeed be considered in the future design of novel biocomposites.</p

Discipline-Specific Employability Skills and Awareness via the Virtual Learning Environment: Piloting an Innovative and Transferable Approach

In the context of increased internationalisation and use of online distance learning in higher education, educators are faced with the challenge of promoting diverse students’ employability in an inclusive, effective and discipline-specific way. Few case studies have demonstrated how employability skills can be embedded within the core online learning. This presentation will address this gap by documenting how discipline-specific skills were systematically identified in a job market analysis, and integrated into the virtual learning environment, in an MSc Global Mental Health programme. Attendees will be provided with practical tools, guidance and reflection prompts

Aqueous one-pot synthesis of epoxy-functional diblock copolymer worms from a single monomer: new anisotropic scaffolds for potential charge storage applications

Nitroxide-functional polymers have garnered considerable interest in recent years and appear to hold promise for energy storage applications. However, their synthesis can be both expensive and time-consuming. Here, we propose a highly convenient method for the preparation of TEMPO-functional diblock copolymer nanoparticles directly in water. Epoxy-functional diblock copolymer worms are synthesized from a single monomer, glycidyl methacrylate (GlyMA), using a three-step, one-pot protocol in aqueous solution via polymerization-induced self-assembly (PISA). First, an initial aqueous emulsion of GlyMA was heated at 85 °C for 9 h to afford an aqueous solution of glycerol monomethacrylate (GMA). Then reversible addition-fragmentation chain transfer (RAFT) polymerization of GMA was conducted in aqueous solution using a dicarboxylic acid-based RAFT agent to produce a water-soluble PGMA homopolymer. Finally, chain extension of this pre-cursor block via RAFT aqueous emulsion polymerization of GlyMA at 50 °C produced amphiphilic diblock copolymer chains that self-assembled in situ to form a 15% w/w aqueous dispersion of diblock copolymer worms. These worms can be derivatized directly using 4-amino-TEMPO in aqueous solution, affording novel crosslinked anisotropic nanoparticles that contain a relatively high density of stable nitroxide radicals for potential charge storage applications</p