Patrick Lacroix-Desmazes

Well-Architectured Poly(dimethylsiloxane)-Containing Copolymers Obtained by Radical Chemistry

3.1. Polysiloxane Macroinitiators 1239 3.1.1. Redox-Initiated Polymerization 1239 3.1.2. Photoinitiated Polymerization 1240 3.1.3. Ozonide Macroinitiators 1241 3.1.4. Bis-(silyl pinacolate) Macroinitiators 1241 3.1.5. Peroxycarbamate Macroinitiators 1241 3.1.6. Peroxyester Macroinitiators 1242 3.1.7. Azo Macroinitiators 1242 3.2. Polysiloxane Macromonomers 1245 3.2.1. Synthesis of Polysiloxane Macromonomers and Copolymerization 1245

The persistent radical effect in nitroxide mediated polymerization: Experimental validity

The free-radical polymerization of styrene has been studied at 123°C in the presence of a betaphosphonylated alkoxyanine (diethyl[(1,1-dimethylethyl)(1-phenylethoxy)amino]-2,2-dimenthylpropyl phosphonate) (stryl-DEPN). The persistent radical effect is undoubtedly observed experimentally until the effect of viscosity on the rate constant of termination is no longer negligible. The kinetic laws of the persistent radical effect allow us to calculate the pseudo equilibrium constant of dissociation/combination between dormant and active species k polystyryl-DEPN = 6.1 x 10 -9 mol . L ―1 at 123°C. We have verified the reliability of this constant by computer simulation in comparision with the experimental data.

Synthesis of poly(chloromethylstyrene-b-styrene) block copolymers by controlled free-radical polymerization

The controlled free-radical polymerization of styrene and chloromethylstyrene monomers in the presence of 2,2,6,6-tetramethyl-1-piperidinyloxyl (TEMPO) has been studied with the aim of synthesizing block copolymers with well-defined structures. First, TEMPO-capped poly(chloromethylstyrene) was prepared. Among several initiating systems [self-initiation, dicumyl peroxide, and 2,2′-azobis(isobutyronitrile)], the last offered the best compromise for obtaining a good control of the polymerization and a fast polymerization rate. The rate of the TEMPO-mediated polymerization of chloromethylstyrene was independent of the initial concentration of TEMPO but unexpectedly higher than the rate of the thermal self-initiated polymerization of chloromethylstyrene. Transfer reactions to the chloromethyl groups were thought to play an important role in the polymerization kinetics and the polydispersity index of the resulting poly(chloromethylstyrene). Second, this first block was used as a macroinitiator in the polymerization of styrene to obtain the desired poly(chloromethylstyrene-b-styrene) block copolymer. The kinetic modeling of the block copolymerization was in good agreement with experimental data. The block copolymers obtained in this work exhibited a low polydispersity index (weight-average molecular weight/number-average molecular weight < 1.5) and could be chemically modified with nucleophilic substitution reactions on the benzylic site, opening the way to a great variety of architectures.

Dispersion polymerization of styrene in ethanol–water media: Monomer partitioning behavior and locus of polymerization

A simulation model has been developed to predict the partitioning behavior of styrene in dispersion polymerization in ethanol–water mixtures. The composition of both the continuous phase and the dispersed phase are quantitatively estimated throughout the polymerization process. The presence of water in the system causes a considerable increase of the styrene partitioning in favor of the particles. Thus, at 70°C and for an initial composition of ethanol/water/styrene = 63.3/26.9/9.8, the concentration of styrene in the particles is about 4.8 times higher than that in the serum instead of about one in pure ethanol. The higher the polymerization temperature, the lower the styrene concentration in the particles; the higher the initial styrene concentration, the higher the styrene concentration in the particles, whereas the partition coefficient is not largely effected. In contrast, neither the interfacial tension nor the final particle size do significantly alter the simulation results. The predicted data from this model have been successfully applied to clarify the mechanisms involved in dispersion polymerization, in terms of stabilization and of kinetic events.

N‐tert‐Butyl‐1‐diethylphosphono‐2,2‐dimethylpropyl nitroxide as counter radical in the controlled free radical polymerization of styrene: kinetic aspects

The controlled free radical polymerization of system with N-tert-butyl-1-diethylphosphono-2,2-dimethylpropyl nitroxide (DEPN) as counter radical was studied. Polymerizations were performed in bulk, with a DEPN-capped polystyryl is alkoxyamine initiator, in the presence of an excess of DEPN nitroxyl free radicals. Kinetics of the polymerzation were followed at 115°C, 125°C and 130°C. The equlibrium rate constant K = k d /k c . of exchange between dormant and active species was determined experimentally from the slope of Ln[styrene] 0 /(styrene] versus time. The obtained Arrhenius relation was the following K(mol.L -1 ) = 1.45 × 10 7 exp (-113.5 kJ.mol -1 /RT), i.e., K=1.9 x 10 -8 mol.L 1 at 125°C. This results is consistent with a much faster polymerization of styrene with DEPN than with Tempo as nitroxyl counter radical (K = 2.1 x 10 -11 mol.L -1 at 125°C determined previously by Fukada).

One pot synthesis of hierarchical porous silica membrane material with dispersed Pt nanoparticles using a microwave-assisted sol–gel route

A versatile sol–gel route has been developed for the preparation of hierarchical porous silica membrane material with highly dispersed platinum nanoparticles (Pt-NPs). The outstanding feature of the “one pot” synthesis developed in this work lies in the successful preparation of a stable complex suspension made of silica sol, multi-scale porogens and Pt nanoparticles. The multi-scale porogens were based on non-ionic triblock copolymers and aqueous latex suspension to create mesopores and macropores, respectively, with finely tuned pore size and organization. For further functionalization of the membranes, Pt nanoparticles of about 4 nm in diameter were prepared by irradiating with microwaves (MW) the Pt precursors added in the starting suspension. This original path is suggested to enable a pre-organization of Pt nanoparticles in the ordered mesoporous structure. The suspensions were then deposited as thin films on either dense or macroporous supports, and further thermally treated at 450 °C to remove the porogen units. Hierarchical porous layers composed of micropores (<2 nm), ordered mesopores (∼4 nm) and macropores (∼70 nm) with or without Pt were prepared and characterized. The resulting membranes are foreseen to exhibit great potential as multifunctional membranes for gas separation coupled with catalytic reaction.

An Emulsifier‐Free RAFT‐Mediated Process for the Efficient Synthesis of Cerium Oxide/Polymer Hybrid Latexes

Hybrid latexes based on cerium oxide nanoparticles are synthesized via an emulsifier-free process of emulsion polymerization employing amphiphatic macro-RAFT agents. Poly(butyl acrylate-co-acrylic acid) random oligomers of various compositions and chain lengths are first obtained by RAFT copolymerization in the presence of a trithiocarbonate as controlling agent. In a second step, the seeded emulsion copolymerization of styrene and methyl acrylate is carried out in the presence of nanoceria with macro-RAFT agents adsorbed at their surface, resulting in a high incorporation efficiency of cerium oxide nanoparticles in the final hybrid latexes, as evidenced by cryo-transmission electron microscopy.

One-pot surfactant-free functional latexes by controlled radical polymerization in ab initio emulsion

Acrylic acid is commonly added to industrial formulations in order to enhance the stability and the properties of the final latexes. Herein, we report the first one-pot surfactant-free batch ab initio emulsion polymerization process to obtain acrylic acid functionalized polymer latexes by controlled radical polymerization. Reverse Iodine Transfer Polymerization (RITP) is successfully used to synthesize stable and uncolored latexes with good control over the molecular weights. The in situ synthesis of amphiphilic poly(acrylic acid-co-butyl acrylate) gradient copolymers, which provide an electrosteric stabilization to the latex, enables the polymerization in a surfactant-free process. The living character of this novel functional latex is demonstrated by successful block copolymer synthesis.

Solubility and Self-Assembly of Amphiphilic Gradient and Block Copolymers in Supercritical CO2

This work aims at demonstrating the interest of gradient copolymers in supercritical CO(2) in comparison with block copolymers. Gradient copolymers exhibit a better solubility in supercritical CO(2) than block copolymers, as attested by cloud point data. The self-assembly of gradient and block copolymers in dense CO(2) has been characterized by Small-Angle Neutron Scattering (SANS), and it is shown that it is not fundamentally modified when changing from block copolymers to gradient copolymers. Therefore, gradient copolymers are advantageous thanks to their easier synthesis and their solubility at lower pressure while maintaining a good ability for self-organization in dense CO(2).

Sonochemical deposition of platinum nanoparticles on polymer beads and their transfer on the pore surface of a silica matrix.

This study reported the sonochemical deposition of platinum on the surface of polystyrene beads (PSBs) and the transfer of obtained Pt nanoparticles into a porous silica matrix using the PSB as a sacrificial template. Platinum nanoparticle deposition was ensured by the sonochemical reduction of Pt(IV) at room temperature in latex solutions containing polystyrene beads in the presence of formic acid under Ar or under Ar/CO atmosphere without any additives. After ultrasonic treatments for few hours, well dispersed Pt nanoparticles within the range of 3-5 nm deposited on PSB were obtained in both studied conditions. Samples were then mixed with TEOS, dried, and heated at 450°C to ensure the PSB removal from the silica matrix. TEM and SEM results clearly show that final silica pore size is within the same order of magnitude than initial PSB. Finally, platinum decorated silica matrix with chosen pore sizes was successfully prepared.