Stéphanie Magnet

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.

Optimization of block copolymer self-assembly through graphoepitaxy: A defectivity study

In this paper we report a synoptic methodology to evaluate and optimize the long-range order induced by graphoepitaxy of block copolymer (BCP) self-assembly. The authors focus the study on a BCP that produces hexagonally packed arrays of cylinders oriented perpendicular to the substrate with the copolymer film thickness greater than the trench depth. Prepatterned structures used in the graphoepitaxy approach have been generated by e-beam lithography on a commercial hydrogen silesquioxane resist. A suitable surface modification was accomplished by grafting a random polystyrene-r-poly(methyl methacrylate) copolymer on the prepatterned surfaces. The polystyrene-b-poly(methyl methacrylate) was spin-coated and annealed in order to generate the desired self-assembly. Since the self-assembly process is based on a thermodynamic mechanism, the induced defectivity needs to be reassessed with respect to the standard lithographic process. Using the cylinder center coordinates, a Delaunay triangulation is performed to find the nearest neighbors. This triangulation enables us to easily locate the disclinations which are characterized by having a number of nearest neighbors different from six. Thus, the number of defects can be quantified precisely. Additionally, this methodology affords an accurate evaluation of both the optimum mesa and trench critical dimensions yielding defect-free surfaces and may be extended to monitor the robustness of the BCP directed self-assembly process. Such diagnostics are critical in the implementation of large scale industrial processes.

Miniemulsion Polymerization Stabilized by a Well-Defined, Amphiphilic Gradient Poly(styrene-co-acrylic acid) Copolymer

The nitroxide-mediated controlled free-radical copolymerization of styrene (St) and acrylic acid (AA) was used to synthesize a well-defined poly(St30%-co-AA70%) amphiphilic gradient copolymer. The latter proved to be an efficient stabilizer in the 45 wt.-% solids content, batch miniemulsion polymerizations of St and of mixtures of methyl methacrylate/n-butyl acrylate (35/65 w/w). With 2,2´-azobisisobutyronitrile as an oil-soluble initiator, polystyrene latexes with a very narrow particle distribution were obtained, whereas the water-soluble initiator, potassium persulfate, led to broad, multimodal particle size distributions. Such results were explained by the contribution of two nucleation mechanisms: droplet nucleation and homogeneous nucleation. In contrast, the poly(methyl methacrylate-co-n-butyl acrylate) latexes exhibited larger particle size and narrower particle size distributions with persulfate initiator, than the polystyrene latexes.

Study and optimization of the parameters governing the block copolymer self-assembly: toward a future integration in lithographic process

In this paper, we present our studies on polystyrene-b-polymethylmethacrylate (PS-b-PMMA) block copolymer systems to produce cylindrical morphology in the thin film configuration. More specifically, we focus on the different accessible parameters to optimize the processing conditions for the self-assembly of this block copolymer. We studied the self-assembly process of the block copolymer film spin-coated on different random brushes obtained by varying several parameters such as the film thickness, and the annealing time and temperature. We have shown that the thin-film morphology (in-plane, out-of-plane or mixed ones) critically depends on those different parameters and that a subtle optimization of them will provide almost defect-free nanostructures. We also examined the morphology of the self assembled features in the interior of the block copolymer thin film after the subsequent removal of the PMMA block structured domain. This process leads to the film top-nanostructures spanning across the whole film thickness. We evidenced also that high aspect-ratio nanostructures in bulk silicon can be obtained with such optimized films through CMOS-compatible dry-etching approach. To conclude, we show that the above-optimized self assembly parameters can be directly combined with 193nm-resist based patterns through the graphoepitaxy approach to achieve useful features for advanced lithography.