Vibrational spectroscopy polymer branching

Spectroscopic techniques are of great importance in polymer science, as they are in all branches of the chemical sciences, and these are dealt with in chapters 3 and 4. NMR is of prime importance as a method for identification and elucidation of the structure of polymer chains, and a complete chapter has been devoted to this technique. In recent years it has become an increasingly sophisticated and correspondingly expensive technique, requiring considerable skill in operating the spectrometer and in interpreting spectra, but it is still available in a simple and routine form in many laboratories. Vibrational spectroscopy encompasses infrared (IR) and Raman. These techniques, IR in... 

Molecular motions in polymers, particularly those types that involve some reorganization of functional groups such as branches, should be amenable to study by vibrational spectroscopy. The spatial movement of functional groups involves a change in the directions of dipole moment and polarizability changes during molecular vibrations. Hence, the measurement of linear dichroism using... 

Infrared spectroscopy is one method used to identify polymers, as discussed in Section 1.9.4. The degree of branching of polymers can also be determined if the absorption bands of the branch groups can be identified. Similarly in copolymers, the relative composition can be obtained if the different types of repeat unit have distinct vibrational modes and thus absorption bands. To make this a quantitative measure of fractional content, the absorbance in each band is measured via the Beer-Lambert law A = eel, where s is the molar absorptivity, c is the concentration of a given species and / is the path length. For a copolymer with two different types of repeat unit the ratio of absorbances yields the ratio of concentrations if the molar absorptivities are known, for example having being measured previously for samples of known composition. 

---