Mass spectrometric studies of synthetic polymers

Matrix assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) is shown to be a sensitive probe for the analysis of the major and minor oligomers produced during novel functionalization reactions whose mechanisms are not yet well established. Complete characterization of all oligomers generated during functionalization reactions provides an essential tool to the synthetic chemist for understanding side reactions. This could give insight in selecting alternative routes or making modifications to the reaction conditions. Some results represent the first application of MALDI-TOF MS to the quantitative analysis of chain end functionalization reactions.; Tandem mass spectrometry (MS/MS) using post-source decay or collisionally induced dissociation allowed the assignment of a specific sequence to an oligomer based on the fragments detected. It was discovered that adipic acid ( A) was not incorporated into every possible position along the backbone of a synthetic polyester composed of neopentyl glycol (G), terephthalic acid (T) a small amount of A. Large fragments not containing A were detected proving that a specific sequence was preferentially formed under the reaction conditions used. The only sequence that can reconcile all the observed peaks is H-(GT)_n- GAG-OH, n = 2–4, where the adipic acid is located in the first interior position.; Negative mode MS/MS spectra generated under electrospray ionization (ESI) conditions are found to be much cleaner than their positive mode counterparts. The covalent anionic charge induces sequential fragmentation of the polymer backbone by nucleophilic attack. The spectra are not complicated by multiple rearrangements or extensive cation exchange as in the positive mode. This particular approach might be the method of choice for polymer sequencing. Negative mode mass spectrometry is rarely used in the structural elucidation of polymers and this work could pave the way for a new method for determining sequence, block length and end group structure while producing less complicated spectra. The positive mode spectra display a greater amount of fragments but not necessarily more information. In either the positive or negative mode, polyester oligomers with different end groups fragment by similar mechanisms. The observed fragments are consistent with rearrangements initiated by the end groups and internal fragments are not formed.