Diffuse reflection spectrophotometry (DRS) for recognition of products of radiolysis in polymers

The mechanism of radiolysis of polymers can be recognized by product analysis and identification of reaction intermediates, followed by their determination. Among product analysis methods, the most appropriate is spectrophotometry. Due to the poor transparency of polymers occurring mostly as powders from the polymerization line, and the opacity or poor transparency of most processed polymers, the best mode of measurement is diffuse reflected light spectrophotometry (DRS) in UV-VIS. Application of the DRS method to simple systems of low molecular weight and the comparison with the transparent system of the same chemical composition has shown a full veracity of the approach and the application to polymer systems is justified. The important feature of the DRS method is the measurement of absorption spectra against unirradiated polymer sample. Therefore only products of radiolysis are shown, because optical disturbance at the surface texture of the sample is compensated and does not interfere with the recorded spectrum. Optical spectra of irradiated polymers are compared with EPR spectra, leading to a more precise identification of products. Several polymeric systems investigated in our laboratory are listed and one of the systems is presented in the paper in detail: radiation chemistry of virgin polypropylene investigated by the DRS, EPR and gravimetry (chain reaction of oxidation, initiated by us pulse of radiation, but proceeding for several months, in the polymer exposed to air). The diffuse reflected light spectrophotometry is very often a key method among other methods of investigation and has proved its usefulness in the investigation of radiation chemistry of many classes of polymers.