Pyrolysis-FTIR spectroscopy

No.52,Dec.l991,p.307-12 DEGRADATION BEHAVIOUR OF POLYURETHANE STUDIED BY LINEAR TEMPERATURE PROGRAMMED PYROLYSIS FTIR SPECTROSCOPY Herzog K... 

Analytical investigations may be undertaken to identify the presence of an ABS polymer, characterize the polymer, or identify nonpolymeric ingredients. Fourier transform infrared (ftir) spectroscopy is the method of choice to identify the presence of an ABS polymer and determine the acrylonitrile—butadiene—styrene ratio of the composite polymer (89,90). Confirmation of the presence of mbber domains is achieved by electron microscopy. Comparison with available physical property data serves to increase confidence in the identification or indicate the presence of unexpected stmctural features. Identification of ABS via pyrolysis gas chromatography (91) and dsc ((92) has also been reported. 

The combination of pyrolysis with GC/FTIR was presented by Davies et al. (2002), who showed that gas chromatography coupled with FTIR spectroscopy can be used as a complementary technique to the conventional GC/MS analysis, by an easier determination of structural isomers (e.g.,p-cresol, m-cresols,p-cresol). 

Methylgermylene, GeHMe, has been detected in the course of a matrix (Ar matrices, 12 K) FTIR spectroscopy study of vacuum pyrolysis of l,l-dimethyl-l-germa-3-thietane and 1,1,3,3-tetramethyl-l-germacyclobutane (equation 1) . 

Linear-temperature controlled pyrolysis with subsequent analysis of the pyrolysates (volatiles and residues) by FTIR spectroscopy can provide information on the thermal degradation mechanisms of polymers including aromatic polyesters (325). Thermal analysis of PS, poly-p-methylstyrene and poly-a-methylstyrene was carried out using evolved-gas IR analysis (302). 

In thermolysis FTIR the sample (typically 200 /ug) is loaded onto a quartz boat, which is inserted straight into a platinum coil filament. With the beam focused several mm above the filament surface, the IR-active gas products from the fast heated sample can be detected in near real-time. Fast thermolysis/FTIR spectroscopy combines rapid-scan FTIR (20 scans/s) with pyrolysis of a material and realtime measurement of the gas spectra [376]. Temperature, mass changes and spectral data of IR active gases are thus measured simultaneously as a function of time during the rapid heating phase. High-resolution vapour phase libraries are used for identification. 

Brill et al. [376,380] have illustrated the application of T-jump/FTIR spectroscopy with rapid thermolysis of various organoazide polymers and hydroxyl-terminated polybutadiene with and without Ti02 and melamine additives. The T-jump/FTIR technique determines the chemistry of fast pyrolysis. 

The production of a variety of smaller molecules from some larger original molecules has fostered the use of pyrolysis as a (destmctive) sample preparation technique. As a result, capillary GC, MS, and FTIR spectroscopy may be used routinely for analysis of synthetic polymers, composites and other complex industrial materials. In pyrolysis experiments sample size and shape, homogeneity and contamination are important issues. Generally, 10-50 /u.g of sample is desirable for direct PyGC, and about twice that for direct PyETIR. 

Although FTIR can readily be utilised for the analysis of pyrolysates, and has some advantages over PyMS and TVA, a disadvantage of PyFTIR is the lower sensitivity relative to mass spectrometry. This explains the limited usage of this complementary technique. The sensitivity of pyrolysis-IR spectroscopy is surpassed by pyrolysis-laser photoacoustic spectroscopy, a combination of filament pyrolysis and CO2 laser photoacoustic detection [838]. 

The thermal cure characteristics, kinetics of thermal degradation and pyrolysis of four different addition cured phenolic resins were investigated using various techniques, including DSC, DMA, FTIR spectroscopy, TGA and X-ray diffraction. Resins investigated were propargyl ether resins and phenyl azo-, phenyl ethynyl-andmaleimide-functional resins. A comparison of the data obtained for all the phenolic resins was made as a function of molecular structure. 12 refs. 

A brief review is presented on techniques for the analysis of polyolefins and additives in polyolefins. Techniques considered include high-temperature GPC combined with FTIR spectroscopy for the analysis of chemical composition as a function of molar mass, crystallisation fiactionation for the analysis of short-chain branching in LLDPE and of polyolefin blends and pyrolysis-gas chromatography-mass spectrometry for the determination of additives, such as antioxidants, in polyolefins. 13 refs. (3rd Annual UNESCO School lUPAC Conference on Macromolecules and Materials Science, Stellenbosch, South Africa, 2000)... 

Pyrolysis of the polymeric precursors was investigated using thermogravimetry (TG, Netzsch STA 409 C/CD) analysis, coupled with an on-line GC-MS-FTIR spectroscopy (FTIR, Bruker Tensor 27). Phase compositions of the pyrolyzied ceramics and the fabricated composites were investigated with X-ray diffractometer (XRD, D/ max-rb with Cu Ka radiation) thereafter the pyrolysis. 

As reported, the thermal decomposition behaviour of amino trimethylene phosphonic acid (ATMP) and l-hydro)yethylidene-l,l-diphosphonic acid (HEDP) have been studied and a comparison of the experimental results from thermal decomposition by TGA-FTIR and pyrolysis GC-MS, together with modelling of the formation reactions, showed the usefulness of the latter method in predicting the possible decomposition products. Thus, pyrolysis GC-MS was used to determine the gaseous decomposition products of ATMP and HEDP at temperatures corresponding to the main decomposition steps detected by TGA-FTIR spectroscopy and, from a comparison of the experimental results with theoretical modelling, it was established that the decomposition process should follow the formation mechanism, i.e. the thermal decomposition can be understood as the reverse reaction of phosphonic acids. 

Apart from the aforementioned sample preparation techniques (SFE, SPE and SPME), other sample collection modes are coupled directly to spectroscopy (e.g. fast pyrolysis and fast thermolysis-FTIR) and spectrometry (e.g. LD-ITMS). 

Irradiation (A>295nm, Ar, 10 K) of matrix-isolated (trimethoxysilyl)carbene produced l,l-dimethoxy-l,2-siloxe-tane which was identified by IR spectroscopy in comparison with ab initio calculations at the RHF/6-31G(d,p) level of theory. The most intense IR absorption was observed at 1104 cm-1 <19960M736>. Similarly, vacuum pyrolysis-matrix isolation Fourier transform infrared (FTIR) and DFT studies of 3,3-dimethyl-3-germa-6-oxabicyclo[3.1.0]-hexane indicated the transient formation of dimethylgermoxetane <1998OM5041>. 

Combined electron ionization mass spectroscopy (EIMS) and matrix isolation FTIR spectroscopic data on vacuum pyrolysis of 1,1-dimethyl-l-germa-3-thietane assisted by theoretical calculations provide a reasonable foundation for mechanistic interpretation of its thermal decomposition (see Section 2.21.6.1, Equation 7) <1998JA5005>. 

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