Synthèse d'agents RAFT macromoléculaires hydrophiles à base d'acide (méth)acrylique ou d'alginate pour l'élaboration de nanoparticules par polymérisation en émulsion

This work describes the synthesis of nanoparticles stabilized by polyelectrolytes from synthetic(poly((meth)acrylic acid)) or natural (alginate) source by controlled free radical polymerization (CRP),namely RAFT, in emulsion. This process is based on the use of a hydrophilic polymer prepared by RAFT (i.e. macroRAFT) which is reactivated in water for the polymerization of a hydrophobic monomer. The formation of amphiphilic block copolymers which self-assemble in situ leads to the formation of nanoparticles. Firstly, we tried to perform the whole process in water. The RAFT polymerization of acrylic acid and methacrylic acid was studied in this context. Well-defined homopolymers were obtained under a large range of conditions, and further used as macroRAFTs in emulsion polymerization of hydrophobic monomers. Stable nanoparticles composed of well-defined amphiphilic block copolymers were produced. It was shown that the control of the polymerization and the nucleation were strongly dependent on the pH. Nevertheless, a good colloidal stability wasobserved in all cases. This “one-pot” process was then extrapolated to the synthesis of particles stabilized by hydrophilic copolymers of N-acryloylmorpholine (NAM) and alginate macromonomer. Nano-objects with various morphologies were obtained. In order to better understand the formation of these morphologies, a model system using a hydrophilic copolymer of NAM and a polyNAM macromonomer obtained by RAFT polymerization was studied in styrene emulsion polymerization.Ces travaux décrivent la synthèse de nanoparticules stabilisées par des polyélectrolytes d’originesynthétique (poly(acide (méth)acrylique)) ou naturelle (alginate) par polymérisation radicalairecontrôlée (PRC) de type RAFT en émulsion. Ce procédé est basé sur l’utilisation d’un polymèrehydrophile obtenu par RAFT (macroRAFT) qui est réactivé dans l’eau pour la polymérisation d’unmonomère hydrophobe. Des copolymères à blocs amphiphiles sont ainsi générés et s’auto-assemblent in situ pour former des nanoparticules. Dans un premier temps, nous avons cherché à conduire l’ensemble du procédé en milieu aqueux. Des études ont ainsi été menées sur la polymérisation RAFTdans l’eau de l’acide acrylique et de l’acide méthacrylique. Des homopolymères bien définis ont été obtenus sur une large gamme de conditions, puis ont été utilisés comme macroRAFTs pour la polymérisation en émulsion de monomères hydrophobes. Des nanoparticules stables constituées de copolymères à blocs amphiphiles bien définis ont été produites. Il a été montré que le contrôle de la polymérisation et la nucléation dépendaient fortement du pH, mais qu’une bonne stabilité colloïdale était néanmoins observée dans tous les cas. Ce procédé "one-pot " a ensuite été extrapolé à la synthèse de particules stabilisées par des copolymères hydrophiles de N-acryloylmorpholine (NAM) et de macromonomères d’alginate. Des nano-objets aux morphologies variées ont été obtenus. Afin de mieux appréhender la formation de ces morphologies, un système modèle employant un copolymère hydrophile de NAM et de macromonomère de polyNAM obtenu par polymérisation RAFT a été étudiépour la polymérisation en émulsion du styrène

Fluorescent labelling and biodistribution of latex nanoparticles formed by surfactant-free RAFT emulsion polymerisation

We report the preparation of a novel range of functional polyacrylamide stabilised polystyrene nanoparticles, obtained by surfactant-free reversible addition-fragmentation chain transfer (RAFT) emulsion polymerisation, their fluorescent tagging, cellular uptake and biodistribution. We show the versatility of the RAFT emulsion process for the design of functional nanoparticles of well-defined size that can be used as drug delivery vectors. Functionalisation with a fluorescent tag offers a useful visualisation tool for tracing, localisation and clearance studies of these carriers in biological models. The studies were carried out by labelling the sterically stabilised latex particles chemically with rhodamine B. The fluorescent particles were incubated in a healthy human renal proximal tubular cell line model, and intravenously injected into a mouse model. Cellular localisation and biodistribution of these particles on the biological models were explored

Kinetic Investigation of the Emulsion Polymerization of Vinylidene Fluoride

Poly(vinylidene fluoride) (PVDF) is among the most produced fluoropolymers, second only to polytetrafluoroethylene. Despite its popularity, the complex microstructural properties achieved during the polymerization are not well documented in the literature. In particular, available models only track the chain length distribution of the polymer, while neglecting the distribution of other important properties, affecting the final behavior of the product. In this work, a 2D kinetic model, evaluating not only the chain length but also the number of terminal double bonds (TDBs) per chain, is developed. The numerical solution of the model is achieved by fractionating the population of polymer chains into classes with a specific number of TDBs and using the method of moments for each class. The model results are compared with experimental evidences for the amount of produced polymer, moles of main chain-ends, number, and weight average molecular weight as well as full molecular weight distribution. Based on this comparison, kinetic parameters are estimated by optimization using genetic algorithm. The model reliability is finally verified using additional experimental data at different temperatures and amounts of initiator

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

World radiocommunication conference 12 : implications for the spectrum eco-system

Spectrum allocation is once more a key issue facing the global telecommunications industry. Largely overlooked in current debates, however, is the World Radiocommunication Conference (WRC). Decisions taken by WRC shape the future roadmap of the telecommunications industry, not least because it has the ability to shape the global spectrum allocation framework. In the debates of WRC-12 it is possible to identify three main issues: enhancement of the international spectrum regulatory framework, regulatory measures required to introduce Cognitive Radio Systems (CRS) technologies; and, additional spectrum allocation to mobile service. WRC-12 eventually decided not to change the current international radio regulations with regard to the first two issues and agreed to the third issue. The main implications of WRC-12 on the spectrum ecosystem are that most of actors are not in support of the concept of spectrum flexibility associated with trading and that the concept of spectrum open access is not under consideration. This is explained by the observation that spectrum trading and spectrum commons weaken state control over spectrum and challenge the main principles and norms of the international spectrum management regime. In addition, the mobile allocation issue has shown the lack of conformity with the main rules of the regime: regional spectrum allocation in the International Telecommunication Union (ITU) three regions, and the resistance to the slow decision making procedures. In conclusion, while the rules and decision-making procedures of the international spectrum management regime were challenged in the WRC-12, the main principles and norms are still accepted by the majority of countries

Rational synthesis of epoxy-functional spheres, worms and vesicles by RAFT aqueous emulsion polymerisation of glycidyl methacrylate

The rational synthesis of epoxy-functional diblock copolymer nano-objects has been achieved via RAFT aqueous emulsion polymerisation of glycidyl methacrylate (GlyMA; aqueous solubility ∼22 g dm-3 at 50 °C) by utilising relatively mild conditions (pH 7, 50 °C) to preserve the epoxy groups. High monomer conversions were achieved within 1 h when using a poly(glycerol monomethacrylate) chain transfer agent with a mean degree of polymerisation (DP) of 28, with GPC analysis indicating relatively narrow molecular weight distributions (Mw/Mn < 1.40) when targeting PGlyMA DPs up to 80. A phase diagram was constructed to identify the synthesis conditions required to access pure spheres, worms or vesicles. Transmission electron microscopy, dynamic light scattering and small-angle X-ray scattering (SAXS) studies indicated the formation of well-defined worms and vesicles when targeting relatively long PGlyMA blocks. These epoxy-functional nano-objects were derivatised via epoxy-thiol chemistry by reaction with l-cysteine in aqueous solution. Finally, an in situ SAXS study was conducted during the RAFT aqueous emulsion polymerisation of GlyMA at 50 °C to examine the nucleation and size evolution of PGMA48-PGlyMA100 diblock copolymer spheres using a bespoke stirrable reaction cell

Anionic block copolymer vesicles act as Trojan horses to enable efficient occlusion of guest species into host calcite crystals

We report a versatile ‘Trojan Horse’ strategy using highly anionic poly(methacrylic acid)–poly(benzyl methacrylate) vesicles to incorporate two types of model payloads, i.e. either silica nanoparticles or an organic dye (fluorescein), within CaCO3 (calcite). Uniform occlusion of silica-loaded vesicles was confirmed by scanning electron microscopy, while thermogravimetry studies indicated extents of vesicle occlusion of up to 9.4% by mass (∼33% by volume). Efficient dye-loaded vesicle occlusion produces highly fluorescent calcite crystals as judged by fluorescence microscopy. In control experiments, silica nanoparticles alone are barely occluded, while only very weakly fluorescent calcite crystals are obtained when using just the fluorescein dye. This new ‘Trojan Horse’ strategy opens up a generic route for the efficient occlusion of various nanoparticles and organic molecules within inorganic host crystals

Block copolymer microparticles comprising inverse bicontinuous phases prepared via polymerization-induced self-assembly

Traditionally, post-polymerization processing routes have been used to obtain a wide range of block copolymer morphologies. However, this self-assembly approach is normally performed at rather low copolymer concentration, which precludes many potential applications. Herein, we report a facile method for the preparation of block copolymer particles exhibiting complex internal morphology via polymerization-induced self-assembly (PISA). More specifically, a series of diblock copolymers were synthesized by reversible addition–fragmentation chain transfer (RAFT) alternating copolymerization of styrene (St) with N-phenylmaleimide (NMI) using a poly(N,N-dimethylacrylamide) (PDMAC) stabilizer as a soluble precursor. Conducting such PISA syntheses in a 50 : 50 w/w ethanol/methyl ethyl ketone (MEK) mixture leads directly to the formation of micrometer-sized PDMAC-P(St-alt-NMI) diblock copolymer particles at 20% w/w solids. Adjusting the degree of polymerization (DP) of the core-forming P(St-alt-NMI) block to target highly asymmetric copolymer compositions provides convenient access to an inverse bicontinuous phase. TEM studies of intermediate structures provide useful insights regarding the mechanism of formation of this phase. SEM studies indicate that the final copolymer particles comprise perforated surface layers and possess nanostructured interiors. In addition, control experiments using 1,4-dioxane suggest that the high chain mobility conferred by the MEK co-solvent is essential for the formation of such inverse bicontinuous structures. One-pot PISA formulations are reproducible and involve only cheap, commercially available starting materials, so they should be readily amenable to scale-up. This augurs well for the potential use of such nanostructured micrometer-sized particles as new organic opacifiers for paints and coatings

End-group ionisation enables the use of poly(N-(2-methacryloyloxy)ethyl pyrrolidone) as an electrosteric stabiliser block for polymerisation-induced self-assembly in aqueous media

A series of near-monodisperse poly(N-2-(methacryloyloxy)ethyl pyrrolidone) (PNMEP) homopolymers was prepared via reversible addition-fragmentation chain transfer (RAFT) solution polymerisation of NMEP in ethanol at 70 °C using a carboxylic acid-functional RAFT agent. The mean degree of polymerisation (DP) was varied from 19 to 89 and acid titration indicated end-group pK a values of 5.07-5.44. Turbidimetry studies indicated that homopolymer cloud points were significantly higher at pH 7 (anionic carboxylate) than at pH 3 (neutral carboxylic acid). Moreover, this enhanced hydrophilic character enabled PNMEP to be used as a steric stabiliser for aqueous polymerisation-induced self-assembly (PISA) syntheses. Thus, a PNMEP 42 precursor was chain-extended via RAFT aqueous dispersion polymerisation of 2-hydroxypropyl methacrylate (HPMA) at 44 °C. A series of PNMEP 42 -PHPMA x diblock copolymers were synthesised using this protocol, with target PHPMA DPs of 150 to 400. High conversions were achieved and a linear evolution in M n with increasing PHPMA DP was observed. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) studies confirmed a spherical morphology in all cases. The nanoparticles flocculated either below pH 4.5 (owing to protonation) or on addition of 60 mM KCl (as a result of charge screening). Thus the anionic end-groups on the PNMEP stabiliser chains make an important contribution to the overall colloidal stability. Similarly, a PNMEP 53 macro-CTA was chain-extended via RAFT aqueous emulsion polymerisation of 2-ethoxyethyl methacrylate (EEMA) at 44 °C. Again, a neutral solution pH was critical for the synthesis of colloidally stable nanoparticles. High conversions were achieved as the target PEEMA DP was varied between 100 and 600 and a linear evolution in molecular weight with PEEMA DP was confirmed by chloroform GPC studies. DLS experiments indicated a monotonic increase in nanoparticle diameter with PEEMA DP and TEM studies confirmed a spherical morphology in each case. In summary, PNMEP can be used as a water-soluble steric stabiliser for aqueous PISA syntheses provided that it contains an anionic carboxylate end-group to enhance its hydrophilic character