Abstract
Synthetic polymers and polymer-based materials are essential and indispensable in many aspects of our life. An increasing demand of polymers with tailor-made properties has led to an extraordinary range of new materials. Most of the methods for characterisation of polymers only produce results on an average over the entire molecular
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weight distribution (MWD) of the material. The combination of multimodal separations and (multistage) mass spectrometry (MS(n)) allows the study of polymer system not only over the whole distribution but also of individual polymer molecules. Therefore, it has its particular value for the characterisation of synthetic polymers. MS has the ability of identifying the elemental composition of individual molecules in the polymer mixtures. Coupled with separation techniques specifically developed for applications in polymer research, MS and MSn show more capabilities to provide detailed information on polymers. In this thesis, polymer properties such as endgroup compositions and monomer sequence were studied by using mass spectrometry with or without separation techniques. A general introduction of the polymer properties, MS and liquid chromatography (LC) and their combined use (LC-MS) is given in Chapter 2 of the thesis. In Chapter 3, a fundamental aspect of mass spectrometry of synthetic polymers, viz. the effect of the charge bearing cation on MS2 is studied. The chapter demonstrates that changing the size of the adduct ion can be used to influence the degree of fragmentation of polymers in tandem mass spectrometry. It also presents a method for discrimination of charge-catalysed and charge-independent fragmentation processes in the polymer system studies. Chapter 4 shows the power of coupling LC to high resolution and high accuracy MSn instruments on homopolymer characterisation. LC-ESI MS2 of the PBA samples identified many initiation and termination reactions that occured during the polymerization. Isomers were observed that originated from different initiation mechanisms. The high accuracy MS spectra allowed discrimination of two isobars with 0.072 Da mass difference. The semi-quantitative study shows that the solvent used for polymerisation strongly influences the polymer composition. Copolymer structure determination is discussed in Chapter 5. Both gradient and isocratic elution LC online coupled with MS showed that the effect of ?-scission during polymerisation on the copolymer composition was very dominant. A further step of using ion mobility spectrometry-mass spectrometry (IMS-MS) to study complex synthetic polymer systems is demonstrated in Chapter 6. Detailed endgroup mapping of PMMA with complex end group combinations was achieved without the need of a preceding time-consuming LC separation. In the very short time span of the experiment, in the tens of milliseconds range, IMS-MS offers full separation and identification of the components of the very complex PMMA system across its entire MWD. Finally Chapter 7 shows an example of using a combination of characterisation techniques to analyse a complex polymer system and its degradation products. Detailed endgroup structures of both original and partially degraded samples were assigned by using LC-MSn. The MS2 experiment on the first 13C isotope peak helped to assign the elemental composition of the fragments without the need of high mass accuracy MS2.
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