Polymers Raman

Another practical example of using Raman in a process environment is to monitor the curing of polymers. Raman spectra as a function of time for the... 

Raman scattering spectroelectrochemical investigations can be carried out for polymers deposited at practically any electrode used in electrochemical investigations (platinum, ITO, glassy carbon and others). In addition, successful application of SERS (surface enhanced Raman spectroscopy) for polypyrrole [124] and polythiophene [117] allows for Raman spectroscopic studies of extremely thin layers of conjugated polymers. Raman spectra of conjugated polymers are sometimes obscured by strong fluorescence. This problem can be effectively resolved by the... 

Raman vibrational frequencies and intensities of octane, dodecane and hexadecane corrformers were calculated using quantum mechanical ab initio methods. The results agreed with various trends observed in the experimental spectra of alkanes, as well as several observations from the experimental Raman spectra of PEs. The data obtained indicated that ab initio calculated Raman data on alkanes provided valuable information regarding the interpretation of polymer Raman spectra, in particular information concerning issues where interpretation based on experimental verification was not possible. 23 refs. 

For conducting polymers, Raman spectroscopy has been specially examined as a way to determine the value of the conjugation length and different methods have been proposed ... 

The utility of the technique is illustrated by the Raman spectrum of PAN/MWCNT composite nanofibers shown in Fig. 6.5 (Hou et al. 2005). Strong Raman scattering (disorder-induced scatter) by MWCNTs in the matrix gives rise to D, G, and D signals. The peak at about 2300cm is due to the -CN group of the polymer. Raman spectroscopy also has been used to study CNTs in composite nanofibers of sUk (Ayutsede et al. 2005, 2006), carbon fibers (Chung et al. 2005), and PAN (Hou et al. 2005). 

Many of the more specialised techniques for the optical examination of specimens have not been covered above, for reasons of space. These include conoscopy [35], infrared microscopy [46], fluorescence microscopy [47], and, of particular interest in connection with polymers, Raman microscopy [2]. 

Yoshino and Shinomiya [20] have published Raman spectra of solutions of various polymers. Raman spectroscopy has many applications in the identification of polymers in which additives obscure the polymer peaks obtained in the IR spectrnm. 

An interesting application of Raman spectroscopy is in the determination of the modulus of pure crystalline forms of a polymer. Raman is very sensitive to... 

For polymers, Raman spectroscopy is particularly useful for characterizing the unsaturation in the monomers and polymers. The general nature of the polymerization... 

Other than the obvious advantages of reduced fluorescence and high resolution, FT Raman is fast, safe and requires mmimal skill, making it a popular analytic tool for the characterization of organic compounds, polymers, inorganic materials and surfaces and has been employed in many biological applications [41]. 

Schrof W, Klingler J, Heckmann W and Horn D 1998 Confocal fluorescence and Raman microscopy in industrial research Colloid Polym. Sc/. 276 577-88... 

Another important breaktlirough occurred with the 1974 development by Laubereau et al [24] of tunable ultrafast IR pulse generation. IR excitation is more selective and reliable than SRS, and IR can be used in pump-probe experiments or combined with anti-Stokes Raman probing (IR-Raman method) [16] Ultrashort IR pulses have been used to study simple liquids and solids, complex liquids, glasses, polymers and even biological systems. 

Woodruff and co-workers introduced the expert system PAIRS [67], a program that is able to analyze IR spectra in the same manner as a spectroscopist would. Chalmers and co-workers [68] used an approach for automated interpretation of Fourier Transform Raman spectra of complex polymers. Andreev and Argirov developed the expert system EXPIRS [69] for the interpretation of IR spectra. EXPIRS provides a hierarchical organization of the characteristic groups that are recognized by peak detection in discrete ames. Penchev et al. [70] recently introduced a computer system that performs searches in spectral libraries and systematic analysis of mixture spectra. It is able to classify IR spectra with the aid of linear discriminant analysis, artificial neural networks, and the method of fe-nearest neighbors. 

Raman Microspectroscopy. Raman spectra of small soflds or small regions of soflds can be obtained at a spatial resolution of about 1 p.m usiag a Raman microprobe. A widespread appHcation is ia the characterization of materials. For example, the Raman microprobe is used to measure lattice strain ia semiconductors (30) and polymers (31,32), and to identify graphitic regions ia diamond films (33). The microprobe has long been employed to identify fluid iaclusions ia minerals (34), and is iacreasiagly popular for identification of iaclusions ia glass (qv) (35). 

The ease of sample handling makes Raman spectroscopy increasingly preferred. Like infrared spectroscopy, Raman scattering can be used to identify functional groups commonly found in polymers, including aromaticity, double bonds, and C bond H stretches. More commonly, the Raman spectmm is used to characterize the degree of crystallinity or the orientation of the polymer chains in such stmctures as tubes, fibers (qv), sheets, powders, and films... 

More recently, Raman spectroscopy has been used to investigate the vibrational spectroscopy of polymer Hquid crystals (46) (see Liquid crystalline materials), the kinetics of polymerization (47) (see Kinetic measurements), synthetic polymers and mbbers (48), and stress and strain in fibers and composites (49) (see Composite materials). The relationship between Raman spectra and the stmcture of conjugated and conducting polymers has been reviewed (50,51). In addition, a general review of ft-Raman studies of polymers has been pubUshed (52). 

Analytical and test methods for the characterization of polyethylene and PP are also used for PB, PMP, and polymers of other higher a-olefins. The C-nmr method as well as k and Raman spectroscopic methods are all used to study the chemical stmcture and stereoregularity of polyolefin resins. In industry, polyolefin stereoregularity is usually estimated by the solvent—extraction method similar to that used for isotactic PP. Intrinsic viscosity measurements of dilute solutions in decahn and tetraHn at elevated temperatures can provide the basis for the molecular weight estimation of PB and PMP with the Mark-Houwiok equation, [rj] = KM. The constants K and d for several polyolefins are given in Table 8. 

H. W. Seisler and K. HoUand-Morit2, Infra Red and Raman Spectroscopy of Polymers Marcel Dekker, Inc., New York, 1980. 

Chain Structure. The chemical composition of poly (vinyhdene chloride) has been confirmed by various techniques, including elemental analysis, x-ray diffraction analysis, degradation studies, and in, Raman, and nmr spectroscopy. The polymer chain is made up of vinyhdene chloride units added head-to-tail ... 

The repeat distance along the chain axis (0.468 nm) is significantly less than that calculated for a planar zigzag stmcture. Therefore, the polymer must be in some other conformation (65—67). Based on k and Raman studies of PVDC single crystals and normal vibration analysis, the best conformation appears to be where the skeletal angle, is 120°, and the torsional of opposite sign) is 32.5°. This conformation is in... 

Raman spectrometry is another variant which has become important. To quote one expert (Purcell 1993), In 1928, the Indian physicist C.V. Raman (later the first Indian Nobel prizewinner) reported the discovery of frequency-shifted lines in the scattered light of transparent substances. The shifted lines, Raman announced, were independent of the exciting radiation and characteristic of the sample itself. It appears that Raman was motivated by a passion to understand the deep blue colour of the Mediterranean. The many uses of this technique include examination of polymers and of silicon for microcircuits (using an exciting wavelength to which silicon is transparent). 

The methods used to characterise polymers are partly familiar ones like X-ray diffraction, Raman spectroscopy and electron microscopy, partly less familiar but widespread ones like neutron scattering and nuclear magnetic resonance, and partly... 

Among the techniques mentioned previously, XPS has the greatest impact on polymer surface analysis. A major additional source of chemical information from polymers comes from IR and Raman spectroscopy methods, These vibrational data can be obtained from the bulk and the surface region, although the information depth is much greater than with AES, XPS, or ISS. 

Figure 5. (a) The ( A, SO,) anion symmetric streching mode of polypropylene glycol)- LiCF,SO, for 0 M ratios of 2000 1 and 6 1. Solid symbols represent experimental data after subtraction of the spectrum corre-ponding to the pure polymer. Solid curves represent a three-component fit. Broken curves represent the individual fitted components, (b) Relative Raman intensities of the fitted profiles for the ( Aj, SO,) anion mode for this system, plotted against square root of the salt concentration, solvated ions ion pairs , triple ions, (c) The molar conductivity of the same system at 293 K. Adapted from A. Ferry, P. Jacobsson, L. M. Torell, Electrnchim. Acta 1995, 40, 2369 and F. M. Gray, Solid State Ionics 1990, 40/41, 637. 

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