Mario Giuffrida

Primary thermal decomposition processes in aliphatic polyamides

Abstract The primary thermal decomposition processes of a series of aliphatic polyamides were investigated by Direct Chemical Ionization (DCI) and Tandem mass spectrometry. Results show that an intramolecular exchange process is the preferred thermal decomposition mechanism for many of the polyamides. Decomposition through a C-H hydrogen transfer reaction appears to occur as a secondary thermal process, except in the case of nylon 3 because of its particular structure. A quite different decomposition pathway is followed by nylons from adipic acid (nylons 6.6 and 11.6), where specific structural factors make the formation of cyclopentanone preferred. These polymers decompose via a C-H hydrogen transfer to nitrogen with the formation of compounds having amine and/or ketoamide end groups. These primary products further decompose or react with the formation of cyclopentanone and compounds bearing amine and/or Schiff base groups.

Biosynthesis and structural characterization of medium-chain-length poly(3-hydroxyalkanoates) produced by Pseudomonas aeruginosa from fatty acids.

In this study, we investigated the ability of Pseudomonas aeruginosa ATCC 27853 to grow and synthesize poly(3-hydroxyalkanoates) (PHAs) from saturated fatty acids with an even number of carbon atoms, from eight to 22, and from oleic acid. In a non-limiting medium, all carbon sources but docosanoic acid supported cell growth and PHA production, with eicosanoic acid giving the highest yield. In magnesium-limiting conditions, higher yields were obtained from sources with up to 16 carbon atoms. Composition was estimated by gas chromatography of methanolyzed samples and (13)C nuclear magnetic resonance. The 3-hydroxyalkanoate units extended from hexanoate to tetradecanoate or tetradecenoate, with octanoate and decanoate as the predominant components. Weight average molecular weights ranged from 78,000 to 316,000. Fast atom bombardment mass spectrometry of partially pyrolyzed samples, coupled to statistical analysis, showed that these PHAs are random copolymers.

Analytical degradation: An approach to the structural analysis of microbial polyesters by different methods

Abstract A sample of pure poly(β-hydroxybutyrate) (PHB) and a sample of poly(β-hydroxybutyrate-co-β-hydroxyvalerate) [P(HB-co-HV)] with a composition ratio HB/HV of 87: 13 were investigated by different degradation methods: (a) direct pyrolysis-mass spectrometry; (b) fast atom bombardment mass spectrometry (FABMS) analysis of the partial pyrolysis products; (c) FABMS analysis of the partial methanolysis products. The pyrolysis products originating from the two microbial polyesters are shown to be thermally labile, so that oligomers higher than the trimer cannot distil undecomposed and remain undetected by electron impact or chemical ionization MS. However, the pyrolysis products can be desorbed by FABMS up to the decamer level. With the partial pyrolysis method it is not possible to obtain reliable composition and sequence distribution data, which may, however, be obtained by the FABMS analysis of the partial methanolysis products of the two samples investigated.

Microstructure of bacterial poly(β-hydroxybutyrate-co-β-hydroxyvalerate) by fast atom bombardment mass spectrometry analysis of the partial pyrolysis products

The partial methanolysis and the partial pyrolysis of bacterially synthesized copolyesters of β-hydroxybutyrate (HB) and β-hydroxyvalerate (HV) have been performed and the oligomers produced have been analyzed by fast atom bombardament mass spectrometry (FAB-MS). An algorithm has been developed to distinguish pure random copolymers from mixtures of random copolymers, using the relative abundances of the oligomers which can be deduced from the FAB-MS spectra.

Primary thermal fragmentation processes in poly(lactic acid) investigated by positive and negative chemical ionization mass spectrometry

Abstract The mechanism of thermal decomposition of poly(lactic acid) was studied by direct pyrolysis-mass spectrometry using EI, CI and NCI ionization methods. It was found that the thermally formed cyclic oligomers of lactic acid are not stable under EI conditions. The results obtained by CI and NCI indicate that intramolecular exchange reactions predominate in the primary thermal fragmentation processes.

Mixtures of cyclic oligomers of poly(lactic acid) analyzed by negative chemical lonization and thermospray mass spectrometry

SummaryAn investigation of the distribution of the cyclic oligomers of poly(lactic acid), formed both by pyrolysis of the polymer and by equilibration with a catalyst, has been performed by Negative Chemical Ionization and Thermospray Mass Spectrometry.The results indicate that the two methods can be used to obtain information on the relative amounts of the oligomers present in the mixture.

Primary thermal fragmentation processes in poly(ethylene oxalate) investigated by mass spectrometry

Abstract The primary thermal decomposition mechanism of poly(ethylene oxalate) (PEO) has been investigated by pyrolysis-mass spectrometry. Several mass spectrometric techniques have been used in order to identify compounds present in the pyrolysis mixture: comparison of electron impact and chemical ionisation spectra, high resolution accurate mass measurements and tandem mass spectrometry (daughter and parent ion spectra). The results obtained indicate that intramolecular exchange reactions predominate in the primary thermal fragmentation processes yielding cyclic oligomers up to tetramer. No other pyrolysis products were detectable under our experimental conditions. PEO, prepared by condensation polymerisation, was shown by 1 H-NMR to contain up to 7% of diethyleneglycol (DEG) units along the polymer chain. A small amount of cyclic oligomers containing DEG units was detected among the pyrolysis products from PEO.

Thermal degradation processes of polyamides investigated by collision activated decomposition mass spectrometry/mass spectrometry

Abstract Linked scanning mass spectrometry was applied to the analysis of the mixture of pyrolysis products obtained from some polyamides, pyrolyzed directly in a mass spectrometer. Collision activated decomposition spectra were obtained in order to induce a higher intensity in the metastable transition. The results indicate that linked scanning mass spectrometry provides a fast method for unambiguously assigning chemical structures through the study of molecular ions, characteristic fragmentations and comparisons of daughter and parent ions of authentic samples.

CHARACTERIZATION BY MASS SPECTROMETRY OF POLY(3-HYDROXYALKANOATES) PRODUCED BY RHODOSPIRILLUM RUBRUM FROM 3-HYDROXYACIDS

The sequence distributions of two microbial copolyesters obtained by fermentation of Rhodospirillum rubrum, grown with 3-hydroxyhexanoic or 3-hydroxyheptanoic acids, were determined by analyzing the oligomers prepared by partial pyrolysis or partial methanolysis of these copolyesters using fast atom bombardment mass spectrometry (FAB-MS). Oligomers up to pentamers were identified in the case of partial pyrolysis and up to tetradecamers in the case of partial methanolysis. The comparison between the experimental and calculated peak intensities of FAB mass spectra allows the calculation of compositions and sequence distributions, which in these copolyesters follow Bernoullian statistics, indicating that they are random terpolyesters.

Thermal decomposition processes in polyhydrazides and polyoxamides investigated by mass spectrometry

Abstract The thermal decomposition processes of some totally aromatic or totally aliphatic polyhydrazides and polyoxamides were studied by direct pyrolysis mass spectrometry, using both chemical ionization and electron impact modes. The results indicate that the primary thermal decomposition processes of these polymers (containing COCO and NRNR linkages) are strongly influenced by structural factors. The polyhydrazide I, derived from isophthalic acid and hydrazine, experiences primary loss of water, producing a polymer with oxadiazole units. The latter thermally decomposes with formation of compounds with nitrile, phenyl, amino and/or acid end groups. The thermal decomposition of the polyhydrazide II, derived from isophthalic acid and N , N ′-dimethylhydrazine, proceeds via an α CH hydrogen transfer process from methyl groups, with formation of pyrolysis products containing secondary amide and/or imine end groups. Hydrolysis of the latter groups leads to the formation of primary amide end groups and subsequent formation of nitrile end groups. The primary thermal decomposition process of the polyhydrazide III, derived from adipic acid and hydrazine, proceeds via a CH hydrogen transfer to the nitrogen atom, with formation of compounds with amine and/or cyclopentanone end groups. In the pyrolysis of this polyhydrazide, secondary thermal fragments are also formed: cyclopentanone, carbon dioxide and compounds with azomethine and isocyanate groups. The polyoxamide IV, derived from oxalic acid and m -phenylenediamine, decomposes via a NH hydrogen transfer process with formation of compounds with amine and/or isocyanate end groups. Finally, the thermal degradation of the polyoxamide V, derived from oxalic acid and ethylenediamine, proceeds via a β CH hydrogen transfer process, with formation of compounds with olefin and amide end groups.