Polystyrene grafting from silica nanoparticles via Nitroxide-Mediated-Polymerization (NMP): synthesis and SANS analysis with contrast variation method,

International audienceWe present a new convenient and efficient “grafting from” method to obtain well defined polystyrene (PS) silica nanoparticles. The method, based on Nitroxide-Mediated Polymerization (NMP), consists to bind covalently the alkoxyamine, which acts as initiator controller agent, at the silica nanoparticles surface in two steps. The first step is a reaction between the aminopropylsilane and the silica particles in order to functionalize the particles surface with amino group. In a second step, the initiating-controlling alkoxyamine moiety is introduced via an over grafting reaction between the amino group and the N-hydroxysuccinimide based MAMA-SG1 activated ester. To simplify both their chemical transformation and the polymerization step, the native silica particles, initially dispersed in water, have been transferred in an organic solvent, the dimethylacetamide, which is also a good solvent for the polystyrene. The synthesis parameters have been optimized for grafting density, conversion rates, and synthesis reproducibility while keeping the colloidal stability and to avoid any aggregation of silica particles induced by the inter-particles interaction evolution during the synthesis. After synthesis, the final grafted objects have been purified and the non-grafted polymer chains formed in the solvent have been washed out by ultra filtration. Then the particles have been studied using Small angle Neutron Scattering (SANS) coupled to neutron contrast variation method. To optimize the contrast conditions, both hydrogenated and deuterated monomers have been used for the synthesis. A refined fitting analysis based on the comparison on two models, a basic core-shell and the Gaussian Pedersen model, enables us to fit nicely the experimental data for both the hydrogenated and deuterated grafted case. Differences are seen between grafting of normal or deuterated chains which can be due to monomer reactivity or to neutron contrast effect variations. The synthesis and the characterization method established in this work constitute a robust and reproducible way to design well defined grafted polymer nanoparticles. These objects will be incorporated in polymer matrices in a further step to create Nanocomposites for polymer reinforcement

Controlling the structure of sequence-defined poly ( phosphodiester)s for optimal MS/MS reading of digital information

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Negative mode MS/MS to read digital information encoded in sequence-defined oligo(urethane)s: A mechanistic study

International audienceMS/MS sequencing is an unrivaled technique to decipher binary information chemically encoded in the backbone of sequence-controlled synthetic polymers constructed with two co-monomers of different mass, arbitrarily designated as the 0- and 1-bit of the ASCII alphabet. Efficiency of this "reading" step relies however on the simplicity of MS/MS patterns, which depends on both polymer chemistry and chain length. In this context, polyurethanes (PUs) were very promising candidates as dissociation of small deprotonated oligomers (n \\textless 8) yielded a single fragment series. The carbamate bond cleavage reaction was hence studied in details to tentatively anticipate the CID behavior of longer chains prior to optimizing their synthesis. In spite of the simplicity of MS/MS spectra, three different mechanisms were evidenced; however, they were not expected to induce MS/MS complexity when activating longer chains, as verified for sequence-controlled PUs containing up to two bytes of information (i.e., 16 co-monomers). In contrast, the ionization step appeared to be an issue: deprotonation yield of the end-group in negative ion mode electrospray was observed to strongly decrease as PU chain length increases. This sensitivity issue was addressed by introducing a second acidic end-group to allow doubly deprotonated oligomers with no impact on their CID behavior. (C) 2017 Elsevier B.V. All rights reserved

In situ formation of stabilizers for the implementation of dispersion nitroxide mediated polymerization of MMA in supercritical carbon dioxide

Controlled dispersion Nitroxide Mediated Polymerization (NMP) of methyl methacrylate (MMA) was successfully carried out for the first time in supercritical carbon dioxide (scCO2) in the presence of CO2-philic perfluorinated surfactant that was generated “in situ”. The control of the MMA polymerization relies on the strategy developed by Charleux et al. that consists of using a SG1-based alkoxyamine, i.e. the block-builder, in the presence of small amount of styrene. In a first step, CO2 soluble polyheptadecafluorodecylacrylate was prepared in scCO2 using block-builder as an alkoxyamine. In a second step, nitroxide SG1 mediated dispersion polymerization of MMA was conducted at 70°C and 300 bar in the presence of 5 w% of SG1 terminated surfactant compared to the monomer. Different monomer to alkoxyamine molar ratios were investigated in order to target different molecular weights. In each case, the monomer conversion was high (>90 %), the experimental molecular weight was in good agreement with the theoretical value and the polydispersity was narrow (Mw/Mn ~1.2). Moreover, after depressurisation of the cell, PMMA was collected as a free flowing powder consisting of small sized microspheres

Dispersion nitroxide mediated polymerization of MMA in supercritical carbon dioxide

Controlled dispersion Nitroxide Mediated Polymerization (NMP) of methyl methacrylate (MMA) was successfully carried out for the first time in supercritical carbon dioxide (scCO2) in the presence of CO2-philic perfluorinated surfactant that was generated “in situ”. The control of the MMA polymerization relies on the strategy developed by Charleux et al. that consists of using a SG1-based alkoxyamine, i.e. the block-builder, in the presence of small amount of styrene. In a first step, CO2 soluble polyheptadecafluorodecylacrylate was prepared in scCO2 using block-builder as an alkoxyamine. In a second step, nitroxide SG1 mediated dispersion polymerization of MMA was conducted at 70°C and 300 bar in the presence of 5 w% of SG1 terminated surfactant compared to the monomer. Different monomer to alkoxyamine molar ratios were investigated in order to target different molecular weights. In each case, the monomer conversion was high (>90 %), the experimental molecular weight was in good agreement with the theoretical value and the polydispersity was narrow (Mw/Mn ~1.2). Moreover, after depressurisation of the cell, PMMA was collected as a free flowing powder consisting of small sized microspheres

Combined nitroxide mediated radical polymerization techniques for block copolymer synthesis

International audienceNitroxide mediated radical polymerization (NMP) is one of the most powerful method for advanced polymer synthesis. However, NMP suffers from some limitations, in particular to mediate the polymerization of unconjugated monomers or to conduct the polymerization of conjugated monomers under low temperatures. The combination of NMP with other reversible-deactivation radical polymerization techniques, such as reversible addition fragmentation chain transfer (RAFT), atom transfer radical polymerization (ATRP) or organometallic mediated radical polymerization (OMRP), offered new possibilities in macromolecular engineering. In this contribution we report different strategies of 'combined NMP', i.e., the exchange of the polymer chain-end controlling agents for sequenced polymerization or the introduction of different polymerization-initiating sites onto alkoxyamines or polymers. (C) 2016 Elsevier Ltd. All rights reserved

A comprehensive kinetic study of the conventional free-radical polymerization of seven-membered cyclic ketene acetals

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Inputs of Macromolecular Engineering in the Design of Injectable Hydrogels Based on Synthetic Thermoresponsive Polymers

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