Laurence Couvreur

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...

Pulsed‐laser radical polymerization and propagation kinetic parameters of some alkyl acrylates

Pulsed-laser photoinitiated polymerization was used to determine, in toluene solution, the propagation kinetic parameters of a series of acrylates with increasing size of the alkyl side group. Transfer to monomer and to toluene did not occur significantly in our PLP conditions and our temperature range since no broadening of the MMD was observed, allowing generally to work with two inflection points. In contrast, depending on the nature of the acrylate and on the PLP conditions, transfer to polymer, and thus long chain branching, can critically interfere. Indeed, the Mark-Houwink-Sakurada parameters, which are used to calculate the absolute molar mass at the inflection point, strongly depend on the polymer structure and thus, should be carefully measured for each PLP sample. Although still preliminary, the results show that the k p s measured in toluene solution present a tendency to continuously decrease when increasing the size of the side group. This observation is conflicting with the reported behaviour for PLP experiments in bulk, revealing a possible solvent effect.

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.

In situ nitroxide-mediated polymerized poly(acrylic acid) as a stabilizer/compatibilizer carbon nanotube/polymer composite

Carbon nanotube (CNT) polymer composites were synthesized via in situ nitroxide-mediated diblock copolymerization. Poly(acrylic acid) (PAA) was chosen as a first block to obtain a precomposite CNT-PAA which is readily dispersible in various solvents including water. The immobilization of the stable poly(acrylic acid) alkoxyamine functionality on the nanotube surface occurs during the synthesis of the first block without CNT prior treatment. The living character of this block is established by spectroscopic methods and the nature of the CNT/PAA interaction is discussed. This living first block offers the opportunity to reinitiate the polymerization of a second block that can be chosen among a wide range of monomers. This versatility is illustrated with a second block containing methyl acrylate (MA) or styrene (S). Scanning and transmission electron microscopies confirm good CNT dispersion in the polymer network, while transmission electron microscopy also spots the anchorage locations of PAA on the CNT surface. Such nanotubes wrapped by diblock copolymers can be dispersed in various polymer matrices to create CNT--polymer composites. Conductivity measurements show that these composites obey a percolation-like power law with a low percolation threshold (less than 0.5 vol%) and a high maximum conductivity (up to 1.5 S/cm at room temperature).