Polymer Spectroscopy and Compositional Analysis

The molecular structure plays an important role in determining the characteristics, properties, and behavior of any polymer during its end use. The elucidation of a polymer structure can be conducted in several ways. Since many years ago, several characterization techniques have been used to analyze basically aspects such as the composition, configuration, and conformation of the chemical groups within the polymer. 

By analyzing the composition of a polymer molecule, the nature of the atoms in the polymer chain and the type of bonding can be inferred. Then, the configuration gives an idea about the chemical state of the polymer, the spatial order of the chemical groups, and the optical characteristics and possible behavior of the whole molecule. The conformation characterizes the geometrical state of a polymer. 

From the composition, the polymer structure can also be inferred if detected differences between two structural elements in the polymer are used. For example, signals for an initiator fraction can be compared with the monomer structure or the functionalizing end group that is, it 

Characterization of polymers can be conducted in several ways, from the oldest and simplest techniques to the most sophisticated and complete spectroscopic characterization techniques. 

The older methods of noninsfrumental chemistry, which still possess high informational value, are those dealing with the chemical analysis of polymers based on searching the number and kind of elements that can occur in a given 

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A comprehensive review of compositional and failure analysis of polymers, which includes many further examples of analysis of contaminants, inclusions, chemical attack, degradation, etc., was published in 2000 [2], It includes details on methodologies, sampling, and sample preparation, and microscopy, infrared spectroscopy, and thermal analysis techniques. 

The chemical structure of polymers has been studied by IR and NMR spectroscopy and chemical analysis. The compositions of all the photoproducts obtained are the same as... 

Thermal analysis techniques are used to study the properties of polymers, blends and composites and to determine the kinetic parameters of their stability and degradation processes.Here the property of a sample is continuously measured as the sample is programmed through a predetermined temperature profile. Among the most common techniques are thermogravimetry (TG) and differential scanning calorimetry (DSC). Dynamic mechanical analysis (DMA) and dielectric spectroscopy are essentially extensions of thermal analysis that can reveal more subtle transitions with temperature as they affect the complex modulus or the dielectric function of the material. 

An important development in Raman spectroscopy has been the coupling cf the spectrometer to an optical microscope. This allows the chemical and structural analysis described above to be applied to sample volumes only 1 across [38]. No more sample preparation is required than that for optical microscopy, and the microscope itself can be used to locate and record the area which is analyzed. This has obvious practical application to the characterization of small impurities or dispersed phases in polymer samples. This instrument, which may be called the micro-Raman spectrometer, the Raman microprobe or the Molecular Optics Laser Examiner [39] has also been applied to the study of mechanical properties in polymer fibers and composites. It can act as a non-invasive strain gauge with 1 fim resolution, and this type of work has recently been reviewed by Meier and Kip [40]. Even if the sample is large and homogeneous, there may be advantages in using the micro-Raman instrument. The microscope... 

The main application areas for complementary size exclusion chromatography-mass spectroscopy (SEC-MS) are measurements of molecular weight (M ) or molecular mass distribution (MWD), polymer characterisation studies, end-group analysis and compositional analysis of copolymers. 

A technique which is extremely powerful for the analysis and characterisation of polymers is one based on the use of controlled chromatography-mass spectroscopy of polymer decomposition techniques such as pyrolysis, followed by chromatography to separate any breakdown product, and, finally, mass spectroscopy, to achieve an unequivocal identification of such pyrolysis products to assist in the elucidation of details of the polymer structure and composition. Detail that can be obtained by such methods includes structural detail of the polymer backbone, branching, end groups, isomeric detail and fine detail in the structure of copolymers. 

Polyester composition can be determined by hydrolytic depolymerization followed by gas chromatography (28) to analyze for monomers, comonomers, oligomers, and other components including side-reaction products (ie, DEG, vinyl groups, aldehydes), plasticizers, and finishes. Mass spectroscopy and infrared spectroscopy can provide valuable composition information, including end group analysis (47,101,102). X-ray fluorescence is commonly used to determine metals content of polymers, from sources including catalysts, delusterants, or tracer materials added for fiber identification purposes (28,102,103). 

Other techniques utilize various types of radiation for the investigation of polymer surfaces (Fig. 2). X-ray photoelectron spectroscopy (XPS) has been known in surface analysis for approximately 23 years and is widely applied for the analysis of the chemical composition of polymer surfaces. It is more commonly referred to as electron spectroscopy for chemical analysis (ESCA) [22]. It is a very widespread technique for surface analysis since a wide range of information can be obtained. The surface is exposed to monochromatic X-rays from e.g. a rotating anode generator or a synchrotron source and the energy spectrum of electrons emitted... 

Perhaps the most revolutionary development has been the application of on-line mass spectroscopic detection for compositional analysis. Polymer composition can be inferred from column retention time or from viscometric and other indirect detection methods, but mass spectroscopy has reduced much of the ambiguity associated with that process. Quantitation of end groups and of co-polymer composition can now be accomplished directly through mass spectroscopy. Mass spectroscopy is particularly well suited as an on-line GPC technique, since common GPC solvents interfere with other on-line detectors, including UV-VIS absorbance, nuclear magnetic resonance and infrared spectroscopic detectors. By contrast, common GPC solvents are readily adaptable to mass spectroscopic interfaces. No detection technique offers a combination of universality of analyte detection, specificity of information, and ease of use comparable to that of mass spectroscopy. 

Composition and structure of newly developed additives are commonly examined by IR, NMR, MS and elemental analysis, e.g. recently developed higher MW antioxidants [115]. Infrared spectroscopy is also well suited to the direct verification of compound composition and quantitative determination of additives in polymers. Gray and Neri [116] have used Soxhlet... 

Since the late 1960 s a few papers have demonstrated compositional analysis of various polymer systans by Raman spectroscopy. For example, Boerio and Yuann (U) developed a method of analysis for copolymers of glycidyl methacrylate with methyl methacrylate and styrene. Sloane and Bramston-Cook (5) analyzed the terpolymer system poly(methyl methacrylate-co-butadiene-co-styrene). The composition of copolymers of styrene-ethylene dimethacrylate and styrene-divinylbenzene was determined by Stokr et (6). Finally, Water (7) demonstrated that Raman spectroscopy could determine the amount of residual monomer in poly(methyl methacrylate) to the % level. This was subsequently lowered to less than 0.1% (8). In spite of its many advantages, the potential of Raman spectroscopy for the analysis of polymer systems has never been fully exploited. 

IQiowledge of parameters such as reactivity ratios, is necessary for synthesis of polymer based resists, and an accurate method of analysis should be useful in various areas associated with resist development such as quality control. Raman spectroscopy provides a convenient, absolute, nondestructive method for compositional analysis of polymer systems which, if an internal standard is present, does not require standards of known composition or ancillary calibration curves. The accuracy, with appropriate selection of experimental conditions such as slit width and integration time, is limited only by the instrumentation. 

Many studies use infrared spectroscopy for quality control and quality analysis in polymer production. It is particularly used for the determination of the composition of copolymers and polymer blends and also for determination of additive and filler contents [90, 91, 92]. 

The feasibility of diffuse reflectance NIR, Fourier transform mid-IR and FT-Raman spectroscopy in combination with multivariate data analysis for in/ on-line compositional analysis of binary polymer blends found in household and industrial recyclates has been reported [121, 122]. In addition, a thorough chemometric analysis of the Raman spectral data was performed. 

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