Polymers vibrational spectroscopy

In addition to providing information about the chemical structure of a polymer, vibrational spectroscopy can also give very useful information about the physical structure, because any two regions of the polymer that differ in the way the repeat units are arranged may exhibit detectable differences in their spectra. Furthermore, measurements of the strength of IR absorption or of Raman scattering can give quantitative information about the composition of any mixture. 

At this stage it may be helpful to note some aspects of polymer vibrational spectroscopy that differ from those of small molecules. Two comprehensive works provide an excellent and thorough review of the subject [11, 12]. 

In all applications discussed in the following chapters the many-dimensional energy surfaces have been Scanned pointwise as a function of some appropriately chosen set of internal coordinates. Energy values thus obtained have been subjected to polynomial fits in order to find the equilibrium geometry and internal, harmonic force constants. In a few cases (polyyne, hydrogen fluoride, hydrogen cyanide) these force constants have been used for an evaluation of vibrational frequencies and phonon dispersion curves within the framework of the harmonic approximation using standard methods of polymer vibrational spectroscopy (see e.g. refs. l8,19 ). 

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). 

W. W. Urban and T. Provder, eds.. Multidimensional Spectroscopy of Polymers Vibrational, NMR, and Tluorescence Techniques, American Chemical Society, Washington, D.C., 1995. 

It is important to mention that for most applications the special form of the force field is not as important as the actual values of the parameters. These parameters are determined in a number of ways, mainly by comparison with experiments, e.g., vibrational spectroscopy. Torsional potentials, which are crucial for polymer configurations and dynamics of polymers, can... 

The development of methods and instrumentation, especially in the high field range, will already open up quite new areas of uses already in the near future. These may at least partly replace and complete solid-state vibration spectroscopy in the polymer field in cases where the amount of material is not the limiting factor. As far as we are able to predict the future, the development of exact quantitative methods of analysis, in particular, will rapidly develop to a high degree of accuracy. 

Chen Z, Shen YR, Somoijai GA. 2002. Studies of polymer surfaces by sum frequency generation vibrational spectroscopy. Annu Rev Phys Chem 53 437-465. 

N.J. Everall, J.M. Chalmers and P.R. Griffiths (Eds.), Vibrational Spectroscopy of Polymers Principles and Practice, Wiley, Chichester, 2007. 

J.M. Chalmers and N.J. Everall, Qualitative and quantitative analysis of plastics, polymers and rubbers by vibrational spectroscopy. In N.J. Everall, J.M. Chalmers and P.R. Griffiths (Eds.), Vibrational Spectroscopy of Polymers Principles and Practice, Wiley, Chichester, 2007, pp. 1-67. 

Both vibrational spectroscopies are valuable tools in the characterization of crystalline polymers. The degree of crystallinity is calculated from the ratio of isolated vibrational modes, specific to the crystalline regions, and a mode whose intensity is not influenced by degree of crystallinity and serves as internal standard. A significant number of studies have used both types of spectroscopy for quantitative crystallinity determination in the polyethylenes [38,74-82] and other semi-crystalline polymers such as polyfethylene terephthalate) [83-85], isotactic poly(propylene) [86,87], polyfaryl ether ether ketone) [88], polyftetra-fluoroethylene) [89,90] and bisphenol A polycarbonate [91]. 

Chen C, Wang J, Even MA, Chen Z (2002) Sum frequency generation vibrational spectroscopy studies on Buried polymer/polymer interfaces. Macromolecules 35 8093-8097... 

Information concerning conformation, tacticity and crystallinity may also be obtained (1). Vibrational transitions accesssible to IR spectroscopy are governed by the selection rule that there must be a change in dipole moment during excitation of the polymer vibrations. Thus symmetric vibrations which are detected by Raman spectroscopy are inaccessible to IR absorption measurements. 

P.D. Coates, S.E. Barnes, M.G. Sibley, E.C. Brown, H.G.M. Edwards and I.J. Scowen, In-process vibrational spectroscopy and ultrasound measurements in polymer melt extrusion. Polymer, 44, 5937-5949 (2003). 

The primary motivation for the development and application of vibrational optical activity lies in the enhanced stereochemical sensitivity that it provides in relation to its two parent spectroscopies, electronic optical activity and ordinary vibrational spectroscopy. Over the past 25 years, optical rotatory dispersion and more recently electronic circular dichroism have provided useful stereochemical information regarding the structure of chiral molecules and polymers in solution however, the detail provided by these spectra has been limited by the broad and diffuse nature of the spectral bands and the difficulty of accurately modeling the spectra theoretically. 

IR spectroscopy is experimentally much simpler as compared to other methods of vibrational spectroscopy. In order to record an IR spectrum, in most cases the polymer is brought onto discs of NaCl or KBr either as a thin solid film (made... 

Furukawa Y (1996) Electronic absorption and vibrational spectroscopies of conjugated conducting polymers. J Phys Chem 100 15644... 

FT-IR has almost become a ubiquitous technique in physical and analytical chemistry and a number of sources can be consulted for details 3,4 5,S). This review will only consider those applications related to polymer systems. A number of prior reviews of the applications of FT-IR have been written The relevant theory of vibrational spectroscopy of polymers will not be covered here as it has been treated in detail in a recent monograph15). An excellent discussion of the experimental aspects of the spectroscopy of polymers is also recommended 16). 

Painter, P. C., Coleman, M. M., Koenig, J. L. Theory of Vibrational Spectroscopy with Application to Polymers, John Wiley and Sons, New York 1981... 

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