Polymer studies Raman spectroscopy

In this presentation, two examples of the use of vibrational spectroscopy to probe water-solid interactions in materials of interest to the food and pharmaceutical sciences are described. First, the interaction of water vapor with hydrophilic amorphous polymers has been investigated. Second, water accessibility in hydrated crystalline versus amorphous sugars has been probed using deuterium exchange. In both of these studies, Raman spectroscopy was used as the method of choice. Raman spectroscopy is especially useful of these types of studies as it is possible to control the environment of the sample more easily than with infrared spectroscopy. 

DEFORMATION STUDIES OF POLYMERS USING RAMAN SPECTROSCOPY... 

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). 

The vibrational spectrum of a metal complex is one of the most convenient and unambigious methods of characterization. However, it has not been possible to study the interactions of metal ions and biological polymers in this way since the number of vibrational bands from the polymer obscure the metal spectrum. The use of laser techniques for Raman spectroscopy now make it very likely that the Raman spectra of metals in the presence of large amounts of biological material will be measured (34). The intensity of Raman lines from metal-ligand vibrations can be... 

Whereas several techniques may thus be used to study a certain characteristic of a polymer sample, for instance IR and Raman spectroscopy and X-ray diffraction as well as NMR may be used to determine or infer the crystallinity level of a sample, different techniques work differently and therefore usually do not measure the same. What this means is that crystallinity levels obtained from the same sample may differ when a different technique is applied, see, for example, ref. [23] and chapter 7 and references therein. However, these differences do not necessarily imply one technique being better than another. In fact these differences may contain useful information on the sample (see, for example, ref. [25]). 

Interaction between sulfathiazole and povidone was studied by Raman spectroscopy, and the nature of the drug-polymer coprecipitates investigated [51]. The nature of the drug (solvation state) and its bonding to the polymer were assessed with respect to sulfathiazole dissolution rate. 

Further details of the theory and application of Raman spectroscopy in polymer studies can be found elsewhere (1. 9). However, vibrational frequencies of functional groups in polymers can be characterized from the spacing of the Raman lines and thus information complementary to IR absorption spectroscopy can be obtained. In addition, since visible radiation is used the technique can be applied to aqueous media in contrast to IR spectroscopy, allowing studies of synthetic polyelectrolytes and biopolymers to be undertaken. Conformation and crystallinity of polymers have also been shown to influence the Raman spectra Q.) while the possibility of studying scattering from small sample volumes in the focussed laser beam (-100 pm diameter) can provide information on localized changes in chemical structure. 

One new technique of potential importance to the study of the interaction of radiation with polymers is time-resolved Raman spectroscopy (14.15). In these... 

Infrared and Raman spectroscopy have been very useful in the study of polymer electrolytes because they provide indications of cation-anion... 

Raman spectroscopy is a powerful tool for probing orientation, stress, and strain. Galiotis et al. have written a review on the determination of stress and strain in composites and fibers using Raman spectroscopy [179]. Young et al. discuss the complexities of correct interpretation of molecular orientation information encoded in Raman spectra of polymers [180]. Caution and a suitable number of control studies are necessary to prevent faulty conclusions. 

Cole reviews the nse of Raman spectroscopy to monitor the curing of different thermoset composite polymer systems, thongh he cautions that it is not suitable for certain materials [215]. Cruz et al. studied the effect of elevated pressure on the cure rate and the degree of cnre of unsaturated polyester and other thermoset materials [216,217]. The approach worked well, though the experimental set up required addi-... 

R.R Paradkar, R.M. Patel, E. Knickerbocker and A. Doufas, Raman spectroscopy for spinline crystallinity measurements. I. Experimental studies, J. Appl. Polym. Sci., 109, 3413-3420 (2008). 

One further attraction of the Raman technique for vibrational studies is that water of bonded OH groups does not cause obscuration of the spectrum but, of course, Raman spectroscopy is useless for studies on water in polymers. At Southampton, excellent spectra of numerous solid mono-, di-, and trisaccharides have been recorded as well as aqueous solutions of some species. It is quite probable that Raman spectra of biologically interesting polymers may be produced shortly8. The ability to examine samples in aqueous regimes obviously has its attractions to the biochemist 1... 

Tanaka, H. and Takemura, T. Studies on the high-pressure phases of polyethylene and polytetrafluoroethylene by Raman spectroscopy. Polymer J. 12, 355 (1980)... 

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