Mass spectral characterization of polymers. Primary thermal fragmentation processes in polyureas

The primary fragmentation processes in the thermal decomposition of polymers were studied in detail on a series of structurally related polyureas by direct pyrolysis with a mass spectrometer. Our results indicate that polyureas I–III undergo a quantitative depolycondensation process analogous to that observed for N-monosubstituted polyurethanes. The thermal decomposition of polyureas IV–VI proceeds by intramolecular hydrogen transfer processes that occur at higher temperatures with respect to depolycondensation. Polycarboxypiperazine VI is decomposed by a single-stage decomposition mechanism that leads to fragments with amino end groups and carbon oxide.     

Direct mass spectrometry of polymers. XII. Thermal fragmentation processes in poly-α-aminoacids

The thermal fragmentation processes in poly-α-aminoacids have been investigated by direct pyrolysis–Mass Spectrometry. The mass spectral data show that the pyrolytic breakdown of polyglycine, polysarcosine, and polyproline leads to the formation of cyclic oligomers. Polyalanine, polyphenylalanine, and polytyrosine decompose yielding compounds with olefin and nitrile end-groups. Finally, in the case of poly-α-methylglutamate, the primary thermal process is the loss of methanol with consequent formation, along the polymer chain, of pyroglutamic units, which yield cyclic dimer as main pyrolysis product.     

Direct mass spectrometry of polymers. X. Primary thermal fragmentation processes in totally aromatic polyesters

The thermal decomposition of a series of isomeric poly-(oxphthaloyloxyphenylenes) (I–IV) and poly(m-hydroxybenzoic acid) (V) was studied by Direct Pyrolysis–Mass Spectrometry. The results indicate that intramolecular exchange reactions predominate in the primary thermal fragmentation processes, causing the formation of cyclic oligomers which are subsequently cleaved to open-chain fragments. The size and relative abundance of the cycles produced appear to be strongly influenced by steric factors, i.e., by the structure (para or meta) of the repeating unit in each polymer. Remarkably, in the case of poly(m-hydroxybenzoic acid) the formation of cyclic oligomers containing up to seven repeating units is observed.     

Solvent Effect on the Rate of Thermal Decomposition of Diacyl Diperoxides

The kinetics of thermal decomposition of didecanoyl diperoxyadipate in different organic solvents have been studied. The primary homolytic dissociation of the peroxide bond (O–O) is accompanied by secondary induced chain decomposition processes. The reaction medium affects both the rate of primary homolytic decomposition and secondary decomposition processes. Correlation equations have been proposed for the rate constants of the reactions under study and physicochemical parameters of the solvents.     

Effects of N-methyl substitution on the thermal stability of polyurethanes and polyureas

Thermogravimetric studies on a series of structurally related polyurethanes and polyureas are reported. The thermal stabilities of N-methylsubstituted polymers are sensibly higher than those of the corresponding unsubstituted (N-H) polymers. Based on a knowledge of the primary thermal fragmentation processes in these polymers, an attempt has been made to correlate chemical structure, mechanism of thermal decomposition and thermal stability.     

Thermal decomposition processes in aromatic-aliphatic polyamides investigated by mass spectrometry

The thermal decomposition processes of some aromatic-aliphatic polymides, derived from terephthalic acid and aliphatic diamines, were studied by flash Pyrolysis-GCMS and by direct Pyrolysis-Mass Spectrometry, using both Chemical lonization and Electron Impact modes. The results indicate that the primary thermal decomposition proceeds via a β-CH hydrogen transfer process, with formation of pyrolysis products containing amide and olefin end-groups. Nitrile end-groups are also formed by dehydration of the amide groups formed in the primary decompostion process.     

Direct mass spectrometry of polymers. VII. Primary thermal fragmentation processes in polycarbonates

The primary fragmentation mechanisms in the thermal decomposition of several polycarbonates were studied by direct pyrolysis into the mass spectrometer. Our results indicate that ester exchange reactions predominate in the primary thermal fragmentation process of polycarbonates, causing the formation of cyclic oligomers.     

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

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.     

Direct mass spectrometry of polymers. VIII. Primary thermal fragmentation processes in polyurethanes

The primary fragmentation mechanisms in the thermal decomposition of several polyurethanes were studied by direct pyrolysis into the mass spectrometer. Ester exchange reactions predominate in the primary thermal fragmentation process, causing the formation of cyclic oligomers, which are subsequently cleaved to open-chain oligomers containing hydroxyl end groups.     

Mechanism of Sonochemical Reactions and Sonoluminescence

Contemporary concepts of the mechanism of sonochemical reactions and sonoluminescence are reviewed. The most elaborated ideas are the thermal theory and the theory of the local charging of cavitation bubbles, wherein the latter theory provides the best fit to experimental data. The primary physical processes occurring upon initiation of sonochemical reactions and sonoluminescence and their similarity and dissimilarity with the corresponding processes relevant to high energy chemistry are considered.     

Dioxin, patterns and source identification

Summary The primary sources of PCDD and PCDF are chemical, thermal, photochemical and enzymatic reactions. Most of the thermal sources result in emissions into the air. Analyses of air, soil and sediment samples indicate combustion processes as the major sources. Only 2,3,7,8-substituted congeners are found in higher animals such as fish and mammals. There is a discrepancy in profiles between sources and environmental reservoirs, which cannot fully be explained.     

Thermal decomposition of peroxy acetyl nitrate CH3C(O)OONO2

The thermal decomposition of peroxy acetyl nitrate (PAN) is investigated by low pressure flash thermolysis of PAN highly diluted in noble gases and subsequent isolation of the products in noble gas matrices at low temperatures and by density functional computations. The IR spectroscopically observed formation of CH3C(O)OO and H2CCO (ketene) besides NO2, CO2, and HOO implies a unimolecular decay pathway for the thermal decomposition of PAN. The major decomposition reaction of PAN is bond fission of the O-N single bond yielding the peroxy radical. The O-O bond fission pathway is a minor route. In the latter case the primary reaction products undergo secondary reactions whose products are spectroscopically identified. No evidence for rearrangement processes as the formation of methyl nitrate is observed. A detailed mapping of the reaction pathways for primary and secondary reactions using quantum chemical calculations is in good agreement with the experiment and predicts homolytic O-N and O-O bond fissions within the PAN molecule as the lowest energetic primary processes. In addition, the first IR spectroscopic characterization of two rotameric forms for the radical CH3C(O)OO is given.     

Thermal reactions of lead(IV) chloride complexes in the solid state. Part IV. Thermolysis of alkali metal hexachloroplumbates

Alkali metal hexachloroplumbates of general formula M₂(I)PbCl₆, with M(I) = K, Rb, Cs, undergo thermal decomposition on heating to 700 K. The thermal processes in the solid state have been studied by differential thermal analysis (DTA) and thermogravimetry (TG) with a derivatograph. The thermolysis occurs in one step M₂(I)PbCl₆→2M(I)Cl_(s)+PbCl_2(s)+Cl_2(g) The experimental TG and DTG curves were used to estimate the enthalpy of thermal dissociation. Based on these curves the kinetic parameters of thermolysis have been evaluated. In the linearization procedure of the kinetic equation.

the methods of Freeman and Carroll, Coats and Redfern, Horowitz and Metzger and Gorbachev were applied. Sixteen f(α) functions which describe the primary mechanism of thermal decomposition of solid substances—nucleation, growth of nuclei, phase boundary reactions and diffusion processes—were used in the least squares error analysis. The dehydration of calcium oxalate monohydrate was performed to confirm the validity of the analytical and computational procedures. The differences in values of the kinetic and thermodynamic parameters for hexachloroplumbates thermolyses have been discussed. It was found that K₂PbCl₆ showed atypical thermal properties. This is probably caused by the different crystal structure of K₂PbCl₆ as compared with those of Rb₂PbCl₆ and Cs₂PbCl₆, as well as the abnormal course of its thermolysis. The thermal properties of alkali metal hexachloroplumbates have been compared with those for analogous compounds of the type M₂(I)M(IV)X₆ (M(IV) = Pt, Te, Tc; X = Cl, Br).     

Thermal degradation chemistry of poly(ethylene naphthalate) – A study by thermal volatilisation analysis

Although the fundamental degradation chemistry of poly(ethylene naphthalate), PEN, is thought to be similar to that of poly(ethylene terephthalate), PET, there is very little evidence in the literature to support this. This paper presents data on the thermal degradation of PEN, in comparison to PET, with particular reference to evolved gas analysis undertaken by thermal volatilisation analysis (TVA). Our thermal degradation studies highlight strong similarities in the degradation behaviour of PET and PEN, despite some evidence of increased thermal stability of PEN in comparison to PET. Identical primary and secondary thermal degradation mechanisms are proposed for PET and PEN, with radical degradation processes thought to dominate at high temperature.     

Temperature-dependent photochemistry of 1,3-diphenylpropenes. The di-pi-methane reaction revisited.

The temperature-dependent photochemical behavior of 1,3-diphenylpropene and several of its 3-substituted derivatives has been investigated over a wide temperature range. The singlet state is found to decay via two unactivated processes, fluorescence and intersystem crossing, and two activated processes, trans,cis isomerization and phenyl-vinyl bridging. The latter activated process yields a diradical intermediate which partitions between ground-state reactant and formation of the di-pi-methane rearrangement product. Kinetic modeling of temperature-dependent singlet decay times and quantum yields of fluorescence, isomerization, di-pi-methane rearrangement, and nonradiative decay provides rate constants and activation parameters for each of the primary and secondary processes. Substituents at the 3-position are found to have little effect on the electronic spectra or unactivated fluorescence and intersystem crossing pathways. However, they do effect the activated primary and secondary processes. Thus, the product ratios are highly temperature dependent.     

Direct mass spectrometry of polymers. XIV. Thermal fragmentation processes in poly-schiff bases

The thermal fragmentation processes in poly-Schiff bases have been investigated by direct pyrolysis–mass spectrometry. The mass spectral data show that the thermal fragmentation occurring in the polymers under investigation is characterized by hydrogen transfer reactions. In the case of a totally aromatic poly-Schiff base (polymer I ), the thermal fragmentation process involves hydrogen transfer irom the methyne group with formation of fragments bearing nitrile and/or phenyl end groups. In the case of aromatic-aliphatic poly-Schiff bases (polymers II–IV ), the hydrogen transfer process occurs from the aliphatic methylene groups. The latter process involves a lower energy and therefore occurs at lower temperatures with respect to the totally aromatic polymer I , with formation of thermal fragments bearing olefin and/or imine end groups. Beside these fragments, several thermal fragmentation compounds are also evolved by multiple hydrogen transfer reactions.     

Application of a computer-based chromatograph for automated water pollution analyses.

A modified head-space analysis technique, coupling thermal extraction with subsequent adsorption of organics on a poly (para 2,6-diphenyl phenylene) oxide adsorbent (Tenax-GC), has been found to be an efficacious tool when combined with gas chromatography for the study and monitoring of low molecular weight organics present in drinking water supplies (1-4). This procedure has allowed for the analysis of volatile organics in the low parts-per-billion range from 1 liter or less of tap water. Because thermal extraction requires smaller sample sizes than required in carbon-chloroform extraction methods and liquid/liquid extractions, the EPA has recently adopted this type of methodology (5,6). Passage of the Safe Water Drinking Act in December of 1974 has mandated that each state assumes the primary responsibility for carrying out the purposes of the legislation (7). Because the Act says that any supplier of water serving 25 individuals or more must comply with these regulations, large-scale monitoring programs will have to be undertaken. It was thus our desire to try to simplify the sample collection and data acquistion and reduction processes as much as possible, in the effort to make the procedure more adaptable for incorporation into routine monitoring programs. Also, automation reduces the experience and number of personnel required to perform the analyses. In addition to analysis of drinking water samples, the automated procedure described hereinafter can also be applied to monitoring industrial plant effluents, waste water treatment processes, and general quality control monitoring of low molecular weight organic compounds.     

Thermal Analysis and Non-isothermal Kinetic Study of Some Pesticides. Part II. Chlorinate derivatives

The thermal behaviour of some commercial pesticides was studied by simultaneous TG/DSC measurements. Kinetic parameters, related to solid-gas phase transition processes, were also carried out by using dynamic TG technique. The kinetics were analysed by using Arrhenius, Satava and Harcourt-Esson equations. The choice of the mathematical expression to insert in these equations was influenced by the shape of the TG plot and other thermal analysis signals. The compounds studied undergo a fusion process followed by a single vaporization process. The latter is well represented by a diffusive process (D₁, D₂ or D₃). The variation of the activation energy values within the range of temperature where the vaporization processes occur was calculated. The enthalpy values of vaporization were also evaluated by using the Clausius-Clapeyron equation. This revised version was published online in August 2006 with corrections to the Cover Date.     

Formation of polyimide from benzophenonetetracarboxylic acid diester complexes with different diamines. 4. Gas-chromatographic study of thermal cyclization of complexes

Thermal cyclization of H complexes is characterized by one rate constant which significantly distinguishes it from thermal cyclization of polyamido acids. The degree of completion of thermal cyclization of the H complex and its rate are determined by diffusion processes related to the structure of the H complex and mobility (softening) of the system during thermal cyclization.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1006–1011, May, 1991.We would like to thank V. V. Shamanin for discussing the results.