Matrix Assisted Laser Desorption Ionization (MALDI) time of flight (ToF) mass spectrometry is a technique that has been used widely to characterize synthetic polymers. Mass spectrometric characterization is an essential tool in the determination of the comonomer composition and functionality distribution of synthetic polymers. Tandem mass spectrometry (MS/MS) is a two-dimensional technique that characterizes synthetic polymers in more detail.
In this dissertation, poly (methyl methacrylate) (PMMA) and poly (methyl acrylate) (PMA) were examined by mass spectrometry (MS) and tandem mass spectrometry (MS/MS). Particular emphasis was devoted to the elucidation of MS/MS fragmentation mechanisms. Such knowledge is a prerequisite for interpreting MS/MS spectra correctly, so that structural information can be deduced from them with confidence. Within the MS/MS studies, a nomenclature was developed to classify MS/MS fragments in a meaningful manner.
Briefly, terminal fragments are labeled by one of the letter codes given in the chart, while internal fragments are labeled by J, K, L, etc. A radical site is indicated by • and the number of repeat units by the subscript. Both, PMMA and PMA chain ionized by alkali metal addition dissociate in the mass spectrometer by homolytic cleavages along the backbone which produce the incipient radical ions an•, bn•, yn• and zn•. These radical ions undergo consecutive, radical-induced reactions which lead to the ultimately observed MS/MS fragments. Radical ions from PMMA as well as PMA dissociate by β-scissions; those from PMA also dissociate by backbiting reactions which produce abundant internal fragments.
Hyperbranched acrylate polymers were analyzed by MALDI mass spectrometry and MS/MS. The MALDI-MS data reveal the composition of the polymer, while the MALDI-MS/MS data provide information about the branching architecture. Upon MS/MS, linear as well as hyperbranched polymers dissociate through 1,5-hydrogen rearrangement over the ester group, as also found for polyesters. This reaction leads to unique products from branched isomers, thereby permitting their differentiation from linear isomers.
A centrally functionalized polyethylene glycol (f-PEG) star has been investigated by MALDI-MS and MS/MS methods. The mass spectra confirm the repeating unit of 44, Da corresponding to [C2H4O1], and reveal identity of the functionality distributions generated in the synthesis. The fragmentation patterns observed in the MALDI-MS/MS experiments provide information about the lengths of the PEG chains attached to the central substituent.
Polyesters are used in many applications, for example, in adhesives, coatings and for packaging. A polyester produced from an aliphatic diacid and an aliphatic diol was analyzed by MALDI mass and tandem mass spectrometry. The MS/MS data show that such polyesters mainly decompose by 1,5-H rearrangement along the ester bond. This behavior is very similar with that found for polyacrylates, where ester moieties are located in the side chains (pendants) instead of the polymer chain.
The discovery of this unique dissociation feature, which has been overlooked thus far, opens the possibility to analyze copolymer sequences and branching geometries in ester-containing polymers based on the fragments generated from competitive and consecutive 1,5-H rearrangements.
Tung oils were also examined by MALDI-MS and MALDI-MS/MS methods. The mass spectra indicate a triglyceride structure with three fatty acid ester groups, mainly C-18 eleostearates. From the MALDI-MS/MS results, it is possible to determine how the fatty acid chains have been derivatized by the Diel-Alder reaction.