DEsign of Solid state experiments for Ionization of copolymeRs in mass Spectrometry – DESIRS

Since the development of soft ionization techniques which have enabled the production of intact high molar mass ions into the gas phase, mass spectrometry has revolutionized the characterization of synthetic polymers. Matrix Assisted Laser Desorption/Ionization (MALDI) has quickly emerged as the method of choice for polymer ionization as it was applicable to more types of synthetic polymers than any other techniques. A key point in the success of a MALDI-MS analysis is sample preparation. This is particularly true for synthetic polymers, which can significantly vary in their solubility, polarity and affinity for different counter ions. Because of the diversity of polymeric materials and the ambiguous role the matrix plays in desorption/ionization of the analyte, no standard protocol is available and method development is still largely a matter of trial and error. A major issue that limits widespread applications of MALDI-MS is the poor knowledge of fundamental processes underlying the desorption/ionization process. As a result, development of MALDI sample preparation methods remains rather empirical and extremely challenging when it comes to complex polymeric systems. The amphiphilic behavior of block copolymer further increases the complexity of the analysis. There is an essential requirement to precise block copolymer characterization as these materials have become a central component of numerous nanotechnologies due to their unique properties in selective solvents and their highly ordered nanostructures. In particular, combinations of PEO with polystyrene (PS) in PS-b-PEO diblock or PS-b-PEO-b-PS triblock copolymers are potentially relevant in terms of industrial applications due to the kind of nanostructuration that can be obtained when PEO block molecular weight reaches 5 kDa.
The final goal of this project is to extend the scope of MALDI application to copolymers and more complex polymers.The scientific challenge underlying this goal is to obtain a rationalization of the MALDI sample preparation. The fundamental key step of the project is to understand the actual influence of the MALDI sample preparation conditions, so that they could be optimized in a rational manner to address the demanding case of amphiphilic copolymers. Then, it is essential to establish relationships between the microstructure of the solid MALDI deposits, the efficiency of the desorption/ionization step, and experimental conditions used to prepare samples.
In this project, we propose to identify the influential experimental parameters on the ionization efficiency, first for PEO and PS homopolymers, then considering PS-b-PEO copolymers. With regards to the large number experimental parameters involved in the MALDI sample preparation, a combined study of MALDI experiments and chemometric analysis will be implemented. Indeed, statistical approaches constitute the most efficient way to evidence synergistic effects between parameters. In parallel, we propose to gain detailed insigths on the MALDI sample solid state architecture using Solid State Nuclear Magnetic Resonance combined with Scanning Electronic Micrsoscopy to access to their morphology and homogeneity. This analytical strategy will allow to draw general rules on MALDI sample structuring to rationalize the development of experimental preparation protocols for homopolymers and copolymers.