Pyrolysis field desorption mass spectrometry of polymers. III. Aliphatic polyamides

Abstract

Pyrolysis field desorption mass spectrometry has been performed from various polyamides such as nylon 6,8,12, and nylon 66. The pyrolytic behaviour of these compounds depends strongly on the solvent and the temperature program employed. Using formic acid as solvent strong thermal fragmentation is observed, while with 1,1,1,3,3,3-hexafluoro-2-propanol almost exclusively molecular ions or cationized molecules of the monomer building block M are produced. With increasing temperature larger clusters of polymeric subunits (M, + Na)+ are generated, but thermal fragmentation on the emitter surface also increases. The cationized molecules dominate all spectra. They are found from M, to M, or M,, depending on the chain length of the polymer subunit. With increasing temperature, the base peak of the spectrum is shifted to the higher mass end and small signals up to m/z 2000 and above are recorded. Thermal products are mainly formed by water elimination ( -18 mu), loss of the acid amide group (-44 mu) after rearrangement and from longer polyamides by loss of the methylene groups ( -42 or 56 mu) by cis-elimination.These thermal fragmentations of the polymeric substances on the emitter surface can be controlled by appropriate emitter heating and correlate directly with the common chemical knowledge of these materials in the liquid or solid phase. Together with the options of integrating recording, high mass resolution and direct isotope determination, the combination of pyrolysis and field desorption mass spectrometry offers a unique tool for characterization of building blocks and high mass sequences in synthetic polymers. ZUSAMMENFASSUNG:Pyrolyse-Felddesorptions-Massenspektrometrie ist zur Untersuchung verschiedener Polyamide wie Nylon 6,8,12 und Nylon 66 verwendet worden. Das pyrolytische Verhalten dieser Verbindungen hangt stark vom Losungsmittel und vom Temperaturprogramm ab. Ameisensaure als Losungsmittel ruft starke thermische Fragmentierung hervor, wiihrend mit 1,1,1,3,3,3-Hexafluoro-2-propanol fast ausschlieBlich Molekiilionen oder kationisierte Molekiile gebildet werden. Mit zunehmender Temperatur entstehen groBere Cluster der polymeren Untereinheit (M, + Na)+ , aber gleichzeitig nimmt die thermische Fragmentierung auf der Emitteroberflache zu. Die kationisierten Molekiile sind in allen Spektren dominant. Sie werden von M, bis M, oder MI, gebildet, je nach Kettenlange der polymeren Untereinheit. Mit zunehmender Temperatur verschiebt sich der Basispeak des Spektrums zu hoheren Massen, und schwache Signale bis m/z 2000 und dariiber werden registriert. Thermische Produkte werden hauptsachlich gebildet durch Wassereliminierung ( -18 mu), Verlust der Saureamid-Gruppe ( -44 mu) nach Umlagerung und von langeren Polyamiden durch Verlust von Methylengruppen ( -42 oder 56 mu) durch cis-Eliminierung.Diese thermische Fragmentierung der Polymeren auf der Emitteroberflache kann durch geeignete Emitterheizung kontrolliert werden und stimmt direkt mit der allgemeinen chemischen Kenntnis von diesen Substanzen in fliissiger und feste...

Synthesis and Structural Characterization of Bioactive PHA and γ-PGA Oligomers for Potential Applications as a Delivery System

“…Heating of polypeptides in the presence of water, leads to hydrolysis of peptide bonds [39]. The cis -eliminations are also known mechanisms of thermal decomposition of polyamides through a 6-membered ring which causes NH-CH 2 bond scission and leads to oligomers with unsaturated alkyl and amide end groups further transformed into nitriles [40,41,42]. Other known products of thermal degradation are cyclic amides, which are result of intramolecular amide exchange [41,42,43].…”

“…The structures of the ions visible on the mass spectrum, which represent the γ-PGA oligomers obtained in esterification carried out in melt, were assigned based on different mechanisms of thermal decomposition of polyamides discussed in literature [40,41,42,43,44]. The proposed structures were placed in Table 2.…”

Thermal decomposition of polyamide-6 in the presence of PVC

“…Montaudo and Puglisi 4) rationalized the production of oligomers of PA-6 as the result of intramolecular rearrangement of a pair of amide groups. A cis-elimination mechanism proposed by Lüderwald 6,7) for the macromolecular chain scission in other aliphatic polyamides explains adequately the formation of nitrile and vinyl end groups in PA-6 as well, hence that of 5-hexenenitrile.…”

“…Pyrolysis-MS performed in the direct inlet probe is a fast and relatively inexpensive method for monitoring the changes in the volatile product formation under pyrolysis of polymers 13) . This method was used also for studying thermal decomposition of polyamides 1,3,4,6,7) and that of PVC in the presence of plasticisers 14) , metals and metallic compounds 15,16) . Pyrolysis-gas chromatography/mass spectrometry supplies detailed information on the volatile thermal decomposition products, and could serve as a basis of understanding primary thermolysis reactions in macromolecules 17) .…”

Multiple cationization of polyethylene glycols in field desorption mass spectrometry: a new approach to extend the mass scale on sector mass spectrometers

“…12 On the basis of such multiply charged ions, MWDs have been determined and discussed. 11 However, the unresolved peaks in each charge state may lead to a higher degree of errors in the MWD determinations.…”