Abstract :
[en] Nowadays, polymer chemists undertake considerable efforts to achieve the preparation of new macromolecules and a perfect control over the macromolecular engineering, i.e. the mass parameters but also over the chain and end-group compositions, topology, etc... is definitively expected. In addition, more complex architectures, such as brush (co)polymers, jellyfish-like topologies..., are required to improve or drastically modify the physicochemical properties of the materials. As a direct consequence of the development of such complex molecular objects, sophisticated techniques are required for the in-depth characterization of the macromolecules, since the exact compositions and structures should be fully and unambiguously identified. Given the fact that the usual characterization tools such as Nuclear Magnetic Resonance (NMR) and Gel Permeation Chromatography (GPC) are extensively used, their abilities have been intensively developed to account for the increasing complexity and diversity of the targeted molecules. Nevertheless, all the usual techniques are averaging methodologies since they only provide pieces of information about the polymer mixture instead of affording data on the individual macromolecules. Since few decades, mass spectrometry (MS) has become as used as NMR and GPC for polymer characterization. In the context of large molecules analysis, MS undoubtedly underwent an impressive craze with the development of two modern ionization procedures, namely Electrospray Ionization (ESI) and Matrix-assisted Laser Desorption/Ionization (MALDI). Those ionization procedures permit the vaporization of macromolecules allowing the intact polymers to be analyzed without a too extensive level of degradation. ESI and MALDI are often considered as soft ionization methods since they offer the possibility to observe ions corresponding to the intact molecules. After their production in the ion source, ions corresponding to the polymer molecules can be mass analyzed by the mass spectrometer and important parameters such as the molecular weight distribution (Mn and Mw), polydispersity index (PDI), the nature of the monomer units and the end-groups can be derived from the measure of the mass-to-charge ratios of the produced ions. In the first part of the present thesis, we studied the MS behavior of different classes of polymers when submitted to ESI and MALDI ionizations. The investigations were devoted to the validation of MS as a truly reliable methodology for fragile polymers such as aliphatic polyesters for instance. In this context, a preliminary MS investigation on semi-telechelic polyethers revealed the importance of the source parameters for the characterization of polymers presenting fragile moieties. We also demonstrated the huge importance of the matrix molecule selection for the MALDI analyses of polymers. In particular, we introduced a new matrix for the MALDI measurements of electroconjugated polymers such as polythiophenes. After the study of the influence of the source parameters on the MS data, a complete study by single stage MS and double stage MS (MS/MS) on newly synthesized polylactides (PLA) was performed. The PLA samples were prepared following original procedures using carbene as catalyst. Finally, to achieve the MS study of PLA ions, we used ion mobility-mass spectrometry (IM-MS) experiments to obtained information on the tridimensional structure of the gas phase PLA ions. In particular, we put a special emphasis on the influence of the charge and size of the polymer chains on their gas-phase conformations. The conclusions derived from the MS/MS and IM-MS results were fully supported by theoretical calculations. In the second part of the thesis, the acquired MS experience was applied to the fine characterization of macromolecules presenting complex architectures obtained by two different polymerization procedures: (i) cobalt-mediated radical polymerization of inter alia acrylonitrile and vinyl acetate and (ii) ring-opening polymerization (ROP) of lactones using non-organometallic catalysts. In particular, mass spectrometry was used to tune the experimental conditions for the ROP of â-lactones using different phosphazenes as catalysts. As an ultimate conclusion, this work points to the very efficient synergy between polymer synthesis, mass spectrometry and theoretical calculations. We believe that this thesis paves the way for innumerable possibilities in the future.
