Evidence for the presence of cage reaction in the initiation step of thermal polymerization of styrenes by field desorption mass spectrometry

Field desorption mass spectrometry (FDMS) was applied to the study of the initiation mechanism of thermal polymerization of styrenes. The FD mass spectrum was measured for a cooligomer of α,α,β-trideuterostyrene and p-methoxystyrene produced by thermal polymerization using ethylbenzene as a solvent, and this was compared with the spectrum of an oligomer of p-methoxystyrene. The above two FD mass spectra showed characteristic differences, depending upon the number of hydrogen and deuterium atoms and upon the presence or absence of the methoxy group, in the oligomers. Molecular species observed in the spectra were identified based on these considerations. As a result, we could distinguish the “true trimer” produced from three monomers from the “cross trimer” produced from fragments of five monomers. It was found that the “true trimer” was the major constituent in the trimer region, and that the “true trimer” was produced mainly by the cage reaction between initiating radicals.     

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

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_n + Na)⁺ are generated, but thermal fragmentation on the emitter surface also increases. The cationized molecules dominate all spectra. They are found from M₃ to M₅ or M₁₅ 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.     

Pyrolysis-field desorption mass spectrometry of coal

Field desorption mass spectrometry of pyrolysis products of coal allows fast fingerprinting of organic and inorganic products. Two main groups of organic species are found: (1) from mass 200 to 800 represents a complex mixture of aliphatic, olefinic, aromatic and heterocyclic guest molecules which are volatilized from coal at low temperatures; (2) obtained at higher temperatures, from mass 800 to >3000 can be assigned to the host structure of the coal and gives a regular, highly reproducible, breakdown pattern. Selected, isolated macerals such as vitrinite, exinite and inertinite are clearly distinguishable by their characteristic peak sequence and intensity envelope in the high mass range. From this knowledge, an estimate of the maceral composition of the investigated bituminous coal is obtained. Using time-resolved pyrolysis consecutively with the generation of low- and high-mass pyrolysates, inorganic salts can be identified and multi-element analysis of metals achieved in the same sample. The time taken for a complete analysis is ≈30 min.     

Surfactant analysis by matrix-assisted laser desorption time-of-flight mass spectrometry

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry was used to characterize nonionic, anionic and cationic surfactants. Rapid mass analyses can be achieved with proper choice of matrix material. The technique is suitable for development as a routine analytical tool.     

Analysis of aromatic polyether dendrimers and dendrimer-linear block copolymers by matrix-assisted laser desorption ionization mass spectrometry

Summary Polyether dendrimers with differing chain end functionalites and molecular topologies were analyzed by MALDI-TOF mass spectrometry. The success of this analytical method is highly dependent on the type of matrix and sample preparation used. Ester and perdeuterophenyl terminated dendrimers with molecular weights up to 14,000 amu were successfully analyzed using an indoleacrylic acid matrix in tetrahydrofuran. Hybrid block copolymers consisting of linear polystyrene or poly (ethylene glycol) chains attached to one or two dendrimers gave spectra with oligomeric resolution in matrices of t-retinoic acid and 2-nitrophenyl octyl ether respectively. The MALDI-TOF results provide access to molecular weight distribution data confirming the results of size exclusion chromatography (SEC) analysis.     

Matrix-assisted laser desorption/ionization imaging mass spectrometry

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) is a powerful tool that enables the simultaneous detection and identification of biomolecules in analytes. MALDI-imaging mass spectrometry (MALDI-IMS) is a two-dimensional MALDI-mass spectrometric technique used to visualize the spatial distribution of biomolecules without extraction, purification, separation, or labeling of biological samples. MALDI-IMS has revealed the characteristic distribution of several biomolecules, including proteins, peptides, amino acids, lipids, carbohydrates, and nucleotides, in various tissues. The versatility of MALDI-IMS has opened a new frontier in several fields such as medicine, agriculture, biology, pharmacology, and pathology. MALDI-IMS has a great potential for discovery of unknown biomarkers. In this review, we describe the methodology and applications of MALDI-IMS for biological samples.     

An innovative approach for the chemical structural characterization of poly(styrene 4-vinylpyridine) copolymers by matrix-assisted laser desorption/ionization time of flight mass spectrometry

Poly(styrene-co-4-vinylpyridine) random copolymers with different molar composition were synthesized by nitroxide-mediated controlled-radical polymerization using 2,2,5-trimethyl-4-phenyl-3-azahexane-3-nitroxide (TIPNO) as a mediator. We record the matrix-assisted laser desorption/ionization time of flight (MALDI-TOF) spectra under various conditions, and we find (at last) that they show mostly intact ions [using 2(-4-hydroxyphenylazo-)benzoic acid as MALDI matrix]. Spectra are highly resolved, and thus they allow for the determination of all end-groups, even some less-abundant ones. Spectra are dominated by intact “dormant” copolymer chains terminated with TIPNO at one end and with (4-Bromo-phenyl)ethyl group (starting fragment) at the other one. Applying the mass analysis of copolymers (MACO) statistical model to the spectra, we show that the MACO/MALDI-TOF mass spectrometry (MS) analysis can be successfully applied to copolymers having a difference between the mass of the comonomers as small as 1 g mol⁻¹ (the styrene and 4-vinylpyridine units are 104.15 and 105.15 g/mol, respectively), which results in overlapping isotopic patterns. The results are accurate: chemical composition evaluated by means of MS agrees with that calculated by ¹H-nuclear magnetic resonance, for all copolymers investigated. This analytical method allows to extract detailed information on the composition of the copolymer samples and their structure. Glass transition temperatures of copolymers were also determined by differential scanning calorimetry. © 2018 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 46976.     

Analysis of mercury species present during coal combustion by thermal desorption

Mercury in coal and its emissions from coal-fired boilers is a topic of primary environmental concern in the United States and Europe. The predominant forms of mercury in coal-fired flue gas are elemental (Hg⁰) and oxidized (Hg²⁺, primarily as HgCl₂). Because Hg²⁺ is more condensable and far more water soluble than Hg⁰, the wide variability in mercury speciation in coal-fired flue gases undermines the total mercury removal efficiency of most mercury emission control technologies. It is important therefore to have an understanding of the behaviour of mercury during coal combustion and the mechanisms of mercury oxidation along the flue gas path. In this study, a temperature programmed decomposition technique was applied in order to acquire an understanding of the mode of decomposition of mercury species during coal combustion. A series of mercury model compounds were used for qualitative calibration. The temperature appearance range of the main mercury species can be arranged in increasing order as HgCl₂ < HgS < HgO < HgSO₄. Different fly ashes with certified and reference values for mercury concentration were used to evaluate the method. This study has shown that the thermal decomposition test is a newly developed efficient method for identifying and quantifying mercury species from coal combustion products.     

Surface oxidation of styrene butadiene copolymers: Study by laser ablation and secondary ion mass spectrometry

The capabilities of ion bombardment and laser ablation coupled to mass spectrometry as independent techniques to investigate the surface thermooxidative stability of polystyrene, polybutadiene polymers, and styrene butadiene rubber (SBR) copolymers were investigated. Surface chemical modifications were detected according to the polymeric structure. The degradation products detected by static secondary ion mass spectrometry appeared at m/z 29, 43, and 55. Their compositions were related to the general formulae C_nH_mO⁺ with n = 1–3 and m = 1–3 for polybutadiene and styrene butadiene copolymers, whereas polystyrene was not affected by the aging treatment. The C_nH_mO⁺ ions result from butadiene unit degradation. The laser ablation ionization Fourier transform ion cyclotron resonance mass‐spectrometry results confirmed the detection of C_nH_mO⁺ ions. Finally, it may be considered that the surface thermooxidative process of SBR copolymers begins with butadiene unit degradation. The development of butadiene unit oxidation showed a dynamic oxidation phase, which coincided with a loss of unsaturation. The influence of the polymer conformation (blocked, branched, and random) on the surface oxidation for 30% styrene SBR compounds was also studied. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1910–1917, 2003     

Laser desorption/ionization time of flight mass spectrometry of phosphorus-containing carbons

Laser desorption/ionization method and time-of-flight mass spectrometry (LDI-TOF) was used to reveal polyphosphates in phosphorus-containing carbons. Phosphorus-containing carbons were obtained by phosphoric acid activation of polymer and lignocellulosic precursor as well as by modification of activated carbon with H₃PO₄. LDI-TOF mass spectrometry revealed polyphosphates with degree of polymerization up to four. The most intensive peaks in LDI-TOF mass spectra correspond to fragments generated by loss of one water molecule from corresponding phosphoric acid ([M −H₂O −H]⁻) in mono, di and triphosphate groups and by loss of two water molecules ([M −2H₂O −H]⁻) in tetraphosphate group.     

Bimolecular and radical hydrogenation of coal studied by field ionization mass spectrometry

Hydrogenation of a low-rank bituminous coal (78 wt% C daf) by decalin (D) and tetralin (T) was carried out at 340–440 °C. Conversion of D and T was determined by g.c. Little conversion of D occurred below 390 °C, indicating little thermal generation of coal radicals. For T, up to 21 H atoms were transferred to 100 C atoms at 380 °C by, it appears, a bimolecular mechanism. F.i.m.s. of samples heated with D and T to 340–440 °C gave ion profiles of seven nominal-mass homologous series of compounds. Results indicated that material with five or more condensed rings was hydrogenated by T between 340 and 380 °C. At 440 °C both donors reacted with some part of the coal by a radical mechanism. The time of exposure of coal to temperatures up to 390 °C could influence coal liquefaction processes.     

Kinetics and mechanism of cationic oligomerization of styrene using poly(styrenesulphonic acid) resin as catalyst

The cationic oligomerization of styrene in benzene using poly(styrenesulphonic acid) resin as catalyst, was carried out under nitrogen. A kinetic model involving initiation, propagation, chain transfer to monomer and spontaneous termination steps, is proposed to fit the experimental kinetic data. It is found that (1) the propagation constant decreases with increasing chain length and remains constant as $\text{n ≧ 5}$; (2) the constant for chain transfer to monomer is also chain length dependent and reaches a maximum at n = 4.     

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry of Vernonia galamensis oil

Matrix-assisted laser desorption/ionization (MALDI) time-of-flight (TOF) mass spectrometry (MS) has been used to identify eight triacylglycerols (TAG) in Vernonia galamensis oil (VO). The TAG include trivernolin, divernoloylstearoylglycerol, divernoloyloleoylglycerol, vernoloyllinoleoylstearoylglycerol, vernoloyllinoleoyloleoylglycerol, and vernoloyldilinoleoylglycerol. Samples for the MALDI/TOF/MS analysis were prepared with alpha-cyano-4-hydroxycinnamic acid (matrix) in an acetonitrile/tetrahydrofuran solvent system. A mol ratio of matrix/VO (44:1) gave reproducible composite spectra, resulting in resolutions greater than 8,000 and signal-to-noise ratios of above 1000 for the most abundant molecular species. 1,3-Dioleoyl-2-stearoylglycerol and 1,2-dioleoyl-3-palmitoylglycerol were used as calibration standards.     

Selective analysis of lipids by thin-layer chromatography blot matrix-assisted laser desorption/ionization imaging mass spectrometry

Thin-layer chromatography (TLC) is an essential method for food composition analyses such as lipid nutrition analysis. TLC can be used to obtain information about the lipid composition of foods; however, it cannot be used for analyses at the molecular level. Recently we developed a new method that combines matrix-assisted laser desorption/ionization imaging mass spectrometry (MALDI-IMS) with TLC-blotting (TLC-Blot-MALDI-IMS). The combination of MALDI-IMS and TLC blotting enabled detailed and sensitive analyses of lipids. In this study, we applied TLC-Blot-MALDI-IMS for analysis of major phospholipids extracted from bluefin tuna. We showed that TLC-Blot-MALDI-IMS analysis could visualize and identify major phospholipids such as phosphatidylethanolamine, phosphatidylinositol, phosphatidylserine, phosphatidylcholine, and sphingomyelin.     

Characterization of petroporphyrins in Gudao residue by ultraviolet-visible spectrophotometry and laser desorption ionization-time of flight mass spectrometry

A porphyrin-containing fraction isolated from the >500 °C residue of Chinese Gudao heavy oil was analyzed using laser desorption ionization-time of flight mass spectrometry (LDI-TOF-MS) for the first time. LDI-TOF-MS was revealed to be suitable for the characterization of petroporphyrins mixture. LDI-TOF mass analysis, combined with UV-vis measurement, indicated that the nickel porphyrins in Gudao residue are a mixture of ETIO homologues (C₂₅-C₃₄) maximizing at C₃₀ and DPEP homologues (C₂₈-C₃₇) maximizing at C₃₁. The ΣDPEP/ΣETIO ratio is about 1.04, suggesting Gudao oil is in the stage of becoming mature.     

Expandable styrene/methyl methacrylate copolymer: Synthesis and determination of VOCs by combined thermogravimetry/differential thermal analysis‐gas chromatography/mass spectrometry

Parts cast of metals using expandable polystyrene foams may have an unacceptable amount of surface defects, such as lustrous carbon. The use of foams made of styrenic/acrylic copolymers can improve the quality of foam molds and metal parts made using such molds. Lost foam copolymer was synthesized by suspension copolymerization of styrene and methyl methacrylate. The polymerization was carried out in the presence of blowing agents. The decomposition products of lost foam beads were studied by a method composed of the thermogravimetry/differential thermal analysis (TG/DTA) and gas chromatography/mass spectrometry (GC/MS). With these systems, the TG/DTA data can be combined with a GC separation and MS identification methods. This combined method improves the analysis of the decomposition products of lost foam beads and enables the precise identification of the amount and the nature of volatile organic compounds (VOCs) trapped during suspension polymerization. The results obtained from the combined method were verified for the nature and amount of VOCs with the results of time‐conversion studies for copolymerization of monomers in the presence of different concentrations of blowing agent. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011