SUMMARY
This work was performed in the frame of the trans-university “Nanodots for Optical and MAgnetic DEtection” NOMADE project granted by the Walloon Region, in collaboration with partners from ULB, the team of Prof. J. L. Delplancke (materials science and electrochemistry laboratory) UMH, the group of Prof. R. Müller (NMR laboratory and molecular imaging) and different teams at ULg. In this project, two types of nanoparticles were considered, gold nanoparticles for their optical properties and iron oxide nanoparticles for magnetic applications. The functionality of these novel nanoparticles has to be tuned by the chemisorption of water soluble polymers well-suited to biomedical applications. Our contribution to this project was focus on the synthesis of novel hydrophilic and functional polymeric ligands for the stabilization of either gold or iron oxides nanoparticles. The main goal of this thesis is thus to report on the synthetic strategies developed to prepare these different polymer ligands to be used in the gold (Chapter 2 and 3) or magnetite (Chaper 4 and 5) nanoparticles synthesis process developed by the partners in order to improve the stability and functionality of the produced suspensions. Besides, the experience acquired during this project has been valorized in exploring synthesis and functionalization of related carbon nanomaterials (Chapters 6 and 7). The results collected in this context are organized in seven chapters as follows:
Chapter I is a general introduction of the research field and is divided in three main parts, 1) major properties of gold nanoparticles, 2) overview of magnetic nanoparticles and 3) short introduction to the Reversible Addition Fragmentation chain Transfer (RAFT) polymerization, main method used for the synthesis of the polymer ligands in this thesis.
Chapter II: A one-step ultrasound-assisted electrochemical process for the synthesis of Quantum Dots is the expertise of the ULB partner. This powerful technique suffers however from strong aggregation of the formed nanoparticles. In this chapter, we have thus investigated the addition of various functional polymers to the sonoelectrochemical bath in order to synthesize stable suspensions of gold nanoparticles in water. α-methoxy-ω-mercapto- poly(ethylene oxide) and poly(vinyl pyrrolidone) were combined in order to build up a coalescence barrier around the gold nanoparticles. The resulting colloidal suspensions were compared to the ones prepared by the more conventional chemical route.
Chapter III: In order to provide gold colloids with an additional thermo-responsive behaviour, nanoparticles were prepared by reduction of HAuCl4 in aqueous solution in presence of poly(N-isopropylacrylamide) (PNIPAM). PNIPAM was prepared by two distinct routes, i.e.
conventional free-radical polymerization that lead to polymer without any reactive end-group and Reversible Addition Fragmentation chain Transfer (RAFT) polymerization. The effect of functionality and polymer molecular mass on the thermal behaviour has been studied and a train-loop-tail model was proposed to account for interaction of PNIPAM with the gold surface.
Chapter IV concerns the elaboration of superparamagnetic magnetite (Fe3O4) nanoparticles stabilized by copolymers consisting of a polyelectrolyte block, i.e. polyacrylic acid and a neutral block, i.e. polyethylene oxide in order to confer a stealth behaviour to the particles.
Two types of stabilizers, i.e., poly(acrylic acid)-b-poly(ethylene oxide) PAA-PEO and poly(acrylic acid)-b-poly(acrylate methoxy poly(ethylenoxide)) PAA-PAMPEO copolymers, were prepared for this purpose by Reversible Addition Fragmentation chain Transfer (RAFT).
The structural and stealthiness properties of these colloids were investigated in relation to the macromolecular architecture of the copolymers. In addition, hyperthermia has been tested with these colloids. In the presence of an alternating magnetic field, these coated nanoparticles are a source of heat.
Chapter V: In the light of chapter IV, magnetite nanoparticles stabilized by temperature- responsive poly(N-isopropylacrylamide) containing block copolymers, i.e. poly(acrylic acid)- b-poly(N-isopropylacrylamide) and poly(acrylic acid)-b-poly(N-isopropylacrylamide)-b- poly(acrylate methoxy poly(ethylene oxide)) were prepared. Particle size analysis confirmed the temperature-responsiveness of the nanoparticles. Moreover, their stealthiness and hyperthermia properties have been assessed in vitro by the haemolytic CH50 test, and thermal measurements under an alternating magnetic field, respectively.
Chapter VI: The RAFT technique developed in the precedent chapters opens the way to other functional copolymers of interest. Poly(acrylonitrile)-b-poly(acrylic acid) (PAN-b-PAA) has been synthesized in a controlled way by this method whatever the starting monomer. Thanks to the availability of these PAN-b-PAA block copolymers, a new and simple method has been developed for the fast preparation of well-defined carbon nanocapsules. It consists of the
micellization of poly(acrylonitrile)-b-poly(acrylic acid) in water at high pH, followed by formation of gold nanoparticles within the PAN core. The gold nanoparticles have the ability to crosslink the PAN core of the micelles, which is beneficial to their conversion into carbon nanocapsules by pyrolysis.
Chapter VII reports on a simple, cheap and tunable approach for the decoration of carbon nanotubes (CNT) by magnetite nanoparticles allowing their orientation in a magnetic field.
Complexing carboxylate groups for the Fe3O4 nanoparticles are anchored to the CNTs using a commercially available radical polymerization initiator, 4,4’-azobis(4-cyanovaleric acid) (V501).
