Joël Belleney

First Nitroxide-Mediated Controlled Free-Radical Polymerization of Acrylic Acid

Controlled poly(acrylic acid) homopolymers were synthesized for the first time by direct nitroxide-mediated polymerization of acrylic acid. The polymerizations were performed in 1,4-dioxane solution at 120 °C, using an alkoxyamine initiator based on the N-tert-butyl-N-(1-diethyl phosphono-2,2-dimethyl propyl) nitroxide, SG1. The kinetics were controlled by the addition of free nitroxide at the beginning of the polymerization and the optimal amount was 9 mol % with respect to the initiator. In this case, whatever the initiator concentration, all polymerizations exhibited the same rate and conversion reached 85−90% within 5 h. Although the rate constant of propagation of acrylic acid is very large, its reactivity is moderated by a low activation−deactivation equilibrium constant between active macroradicals and SG1-capped dormant chains. Various alkoxyamine concentrations were investigated to target different molar masses. At high initiator concentrations, the number-average molar mass, Mn, increased linear...

Nitroxide-mediated copolymerization of methacrylic acid with sodium 4-styrene sulfonate: towards new water-soluble macroalkoxyamines for the synthesis of amphiphilic block copolymers and nanoparticles

The SG1-mediated copolymerization of methacrylic acid (MAA) and 4-styrene sulfonate (SS) was studied in dimethylsulfoxide solution at 76 °C, first, to determine the reactivity ratios in such conditions and second, to check the living character of the reaction at low molar fraction of SS. The reactivity ratios in the terminal model were rMAA = 0.44 and rSS = 1.34 indicating a favored incorporation of SS at the beginning of the copolymerization. All characteristics of a controlled/living system were observed, in good agreement with an efficient deactivation of the propagating radicals by the nitroxide SG1, via probable formation of an SS terminal subunit-based alkoxyamine. The method was shown to be particularly well-suited for the design of living polymers intended to be used as hydrophilic macroinitiators for the synthesis of amphiphilic block copolymers. This was demonstrated in both solution polymerization and ab initio, batch emulsion polymerization. The latter process allowed well-defined block copolymer nanoparticles to be formed at low temperature, in a single step, by simultaneous chain growth and self-assembling.

Anionic polymerization of d,l-lactide initiated by lithium diisopropylamide

The anionic polymerization of d,l-lactide initiated by lithium diisopropylamide.monoTHF complex was performed in different solvents and at various temperatures. No polymerization took place in THF solution. In dioxane at 25°C the polymerization is fast and goes up to completion in few minutes. In toluene, due to solubility requirements, polymerizations were run at 70°C. At initial stage of polymerization Mw/Mns were quite narrow, but at higher conversion a significant broadening occurred due to transesterification reactions. The latter were identified by 13C NMR analysis, while MALDI-TOF spectra revealed the simultaneous presence of cyclic and linear oligomers substantiating the occurrence of both intra and inter ester exchange processes. At low conversion, polymers exhibited a highly syndiotactic microstructure.

Hydrogen bonded supramolecular polymers in protic solvents: role of multitopicity

We describe the synthesis of macromolecular amphiphiles of various molar masses containing well-defined hydrophobic groups incorporating urea moieties. All compounds have the same proportion of associative hydrophobic groups and solubilising POE chains. However, a strong influence of both the number of associative groups per chain and the polydispersity is demonstrated. In water, where the interactions between stickers are strong, the monomer (bearing a single sticker) self-assembles into filaments, but all other compounds with more than one sticker per chain are insoluble. In methanol, where the interactions between stickers are weaker, neither the monomer nor the monodispersed dimer is assembled, whereas polydispersed chains with an average number of 2 or 3 stickers per chain self-assemble into filaments, leading to macroscopic gelation.