Pyrolysis compounds

Montaudo and co-workers have used direct pyrolysis mass spectrometry (DPMS) to analyse the high-temperature (>500°C) pyrolysis compounds evolved from several condensation polymers, including poly(bisphenol-A-carbonate) [69], poly(ether sulfone) (PES) and poly(phenylene oxide) (PPO) [72] and poly(phenylene sulfide) (PPS) [73]. Additionally, in order to obtain data on the involatile charred residue formed during the isothermal pyrolysis process, the pyrolysis residue was subjected to aminolysis, and then the aminolyzed residue analysed using fast atom bombardment (FAB) MS. During the DPMS measurements, EI-MS scans were made every 3 s continuously over the mass range 10-1,000 Da with an interscan time of 3 s. 

As an example of the form of the information that may be derived from a pyrolysis-MS, Figure 26 [69] shows the structure of the polycarbonate (PC) and the EI-MS spectra of pyrolysis compounds obtained by DPMS of poly(bisphenol-A-carbonate) at three different probe temperatures corresponding to the three TIC (total ion current) maxima shown in Figure 27(b) Figure 27 compares the MS-TIC curve with those obtained from thermogravimetry. (The TIC trace is the sum of the relative abundances of all the ions in each mass spectrum plotted against the time (or number of scans) in a data collection sequence [70].)... 

Figure 26 Structure of PC and El mass spectra of pyrolysis compounds obtained by DPMS of poly(bisphenol-A-carbonate) at probe temperatures of (a) 380°C, (b) 500°C and (c) 550°C. Reprinted with permission from Puglisi et al. [69]. Copyright 1999, American Chemical Society.

These workers observed that during Curie Point flash pyrolysis compounds which are reasonably volatile at elevated temperatures do not fragment on the pyrolyser wire but simply evaporate from it. Thus it appeared possible for them that the organic matter present in soils can be characterized and identified very rapidly without any sample pretreatment by direct evaporation/pyrolysis of whole samples. 

Pyrolysis-field ionization MS performed on natural rubber at 315° C [6] generated the spectrum shown in Figure 6.1.2. The results from Py-FI MS show that the main pyrolysis compounds are oligomers of isoprene corresponding to m/z = (68)k where k =1,2. .. 19. However, at trace level other series are present [6] such as m/z = (68)k +... 

From the methylated pectin, the main pyrolysis compound seems to be 4-(hydroxymethyl)-butyrolactone. Two main nitrogenous compounds are formed from amidated pectin, hydroxypyridine and pyrrol-2-carboxaldehyde. Their formation can be explained by the foilowing reactions ... 

On the other hand, a significant number of chlorinated compounds were obtained in pyrolysis. This indicated that chlorinated fragments generated in the intermediate steps of the chlorination process are still present in lignin. They generate by pyrolysis compounds such as chloroguaiacols, chloromethylguaiacols, etc. 

In a further application of this methodology to the Elaeocarpus alkaloid elaeokanine A, Weinreb et al. prepared Diels-Alder precursor 43 (Scheme 2-XV).86,90 On hot tube pyrolysis, compound 43 underwent a cheletropic loss of sulfur dioxide as well as acetic acid elimination to generate an intermediate diene/iV-acylimine, which cyclized to an indoli-... 

The differences observed are probably to some extent due to different reaction conditions. A more systematic study by Rees and co-workers shows that variously substituted sulfilimines (e.g., 125), tetrazoles (128), and oxadiazolones (131) give both carbodiimides (126) and benzimidazoles (129 and 130) together with the interesting cycIopenta[d]pyrimidines 127 on flash vacuum pyrolysis.Compounds 126 and 127 were also obtained by photolysis of 125 and 128 (Scheme 23). The formation of all the products can be rationalized with the aid of a common intermediate, the imidoyl-nitrene 132 (Scheme 24) which either isomerizes to the carbodiimide or... 

On pyrolysis, compounds of the type R2PC1=NS02X, where R = Cl, Me, or Ph and X = F or Cl, give R2POCI and polymeric sulphanuric derivatives [NS(0)X] ,4 while analogous longer-chain species such as... 

Mass spectra of pyrolysis compounds of poly-e-caprolacton evolved at 400°C in (a) El (b) NH3 Cl (c) NH3 NCI ionization methods. (Reprinted with permission from Ref. 32. Cop) ght 1986... 

DPMS since the resulting mass spectra contain more intense molecular ions and therefore the identification of pyrolysis compounds is easier. 

Mass spectra of pyrolysis compounds of poly(neopentylene carbonate) obtained by (a) DPMS El (b) DPMS Cl (c) Isobutane DCI. (Reprinted from Ref. 37, copyright 1991, with permission... 

The DPMS experiment also allows the collection of the single ion current (SIC) curve of specific pyrolysis compounds evolved as a function of the temperature. A typical application consists in the detection of residual low molecular mass compounds (oligomers, additives, solvents) eventually contained in the pol)uner sample. Due to the high vacuum, the existing preformed compounds may distill undecomposed, as the temperature increases. ... 

Mass spectra of pyrolysis compounds detected in the DPMS of polystyrenetetrasulphide (a) El (b) Cl. (Reprinted from Ref. 28, Copyright 1994, with permission from Elsevier Science.)... 

The GC/MS pyrogram of PST (Figure 5.10) obtained by pyrolysis at 400°C shows a limited number of pyrolysis compounds with respect to DPMS. The most abundant pyrolysis compound (peak 1) is due to styrene, while peak 2 corresponds to styrene sulfide and peak 3 is due to Sg (octasulfur ring). The broad and flat shape of the latter peak is most likely due to the condensation of elemental sulfur on cold spots and successive slow evaporation as Sg. The peaks 4 and 5 are due to two isomeric thiophenes 2,4-diphenylthiophene and 2,5-diphenylthiophene. ... 

Another case may occur when primary pyrolysis products quickly react among themselves, in the condensed phase, so that they are detected together with the products of further reaction. The latter situation occurs in the pyrolysis of Nylon 6,6 (Ny66), where a specific structural effect due to the adipic acid unit is responsible for the formation of very reactive pyrolysis compounds. ... 

The structure of this compound suggests that the ion at m/z 209 may originate from further thermal degradation of the primary pyrolysis compounds (molar mass 226), possessing cyclopentanone and amino chain ends, which are very reactive species and immediately react to produce Shiff-bases by water elimination (Scheme 5.6b). The monomeric oligomer also reacts... 

Isobuthane Cl mass spetcmm of pyrolysis compounds evolved at 400°C in the DPMS of Nylon 66. (Reprinted with permission from Ref. 69. Copyright 1987 American Chemical Society.)... 

A disproportionation reaction of the bisphenol A unit (Scheme 5.8d), with consequent polymer chain cleavage, accotmts for fhe formation of pyrolysis compounds with phenyl and isopropenyl end-groups, such as phenol (ion m/z 94, Figure 5.19d) and isopropenyl phenol. 

The El mass spectrum obtained at 520°C from PEI is reported in Figure 5.20 and shows the presence of mass peaks up to 830 Daltons. The structures of the pyrolysis compounds, given in Table 5.3, suggest the occurrence of several thermal degradation processes (Scheme 5.9a-g). 

The most abundant pyrolysis compounds detected in the major degradation step (Figure 5.20) possess intact phthalimide rings containing tire aromatic... 

El mass spectrum of pyrolysis compounds evolved in the DPMS of a PEI sample, at 520°C. (Reproduced from Ref. 38, Copyright 1999, by permission of Wiley-VCH Publications.)... 

Furthermore, pyrolysis compounds containing phthalimide units, with the phenyl rings substituted with H/OH and/or bisphenol A, are formed by the scission of ether bridges (Scheme 5.9b-c), whereas compounds with N-H and/or N-phenyl as end-groups may be formed by the scission of phenyl-phfhalimide bonds (Scheme 5.9d). 

The temperature time-resolved evolution profiles of some relevant pyrolysis compounds of PEI (Figure 5.21) indicate that compounds generated from the scission of isopropenyl and ether bridges (e.g., ions at m/z 518 and 632) are evolved exclusively within the first TIC maximum, indicating that these bonds are tiie weakest units. 

The structures of the thermal degradation products obtained in the DPMS of PC/Ny6 blend permitted the identification of the chemical reactions occurring at higher temperatures. The Cl spectrum of PC/Ny6 blend (Figure 5.23) contains the ions at miz 114 and 509 corresponding to protonated molecular ions of caprolactam and cyclic dimer of PC, respectively. The peak at m/z 112 can be assigned to an unsaturated aliphatic isocyanate whereas the ion at m/z 324 corresponds to an unsaturated ester (Table 5.4). The peak at m/z 367 may possess an open-chain isocyanate-ester or a cyclic urethane-ester structure. TTie pyrolysis compounds containing... 

The evolution profiles of these ions (Figure 5.24) indicate that the imsatur-ated aliphatic isocyanate (ion at m/z 112) is evolved at a lower temperature than the ester-containing pyrolysis compounds (ions at m/z 324 and 367). This suggests that the direct amide/carbonate exchange reaction takes place... 

The TIC curve of PC/PBT blend obtained by Cl DPMS is shown in Figure 5.26, together with the temperature-hme resolved evoluhon profiles of some of the most important pyrolysis compounds. The evolution of... 

THM-GC analysis of the cured Burmese lacquer results in a series of straight-chain and branched-chain alkyl benzenes ranging from toluene to dodecyl benzene, and Cg- to Ciy-alkanes and alkenes. These products are similar in composition to the products obtained by conventional pyrolysis. Compounds corresponding to peaks marked with an asterisk are FAMES that are products of the THM reaction and... 

Direct pyrolysis in the ion source of a mass spectrometer (DPy-MS) operating both in electron impact and chemical ionisation modes was used in these studies. Flash Py-GC-MS was also used in the case of polythiomethylene to confirm the DPy-MS results. The overall evidence indicated that the primary thermal decomposition of these polymers yielded a wide range of cyclic sulfides by an intramolecular exchange process. A 3-CH hydrogen transfer reaction, occurring in parallel with the former process, produced primary pyrolysis compounds with SH end-groups. 

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