Absorption synthetic polar polymers

Figure 2.6 THz absorption spectra of synthetic polar polymers recorded with powdered samples dispersed in a polyethylene matrix. ABS acrylonitrile-butadiene-styrene-ter-polymer PET poly...

In most cases, the THz absorption spectra of polymers do not exhibit specific features, but are characterized by absorption coefficients that increase monotoni-cally with frequency. Some typical absorption spectra of synthetic polar polymers are presented in Figure 2.6. Unpolar polymers including polyethylene, polypropylene and poly(tetrafluoroethylene) absorb only weakly (at 1 THz, a is five- to 20-fold less than for the polar polymers in Figure 2.6). Some typical spectra of unpolar polymers are presented in Figure 2.7. 

In the case of synthetic optically active polymers, the intuitive meaning of a CD signal intensity is very similar to that of UV spectroscopy, with the additional dimension of the subtracted absorption between left and right circularly polarized light.37 Absorption of light obeys the Beer-Lambert law, and thus CD intensity is defined as Ae = eL - eR = (AL - AR)/cl, where Ae is the... 

Z values have been widely used to correlate other solvent-sensitive processes with solvent polarity, e.g. the a absorption of haloalkanes [61], the n n and n n absorption of 4-methyl-3-penten-2-one [62], the n n absorption of phenol blue [62], the CT absorption of tropylium iodide [63], as well as many kinetic data (Menschutkin reactions, Finkelstein reactions, etc. [62]). Copol5mierized pyridinium iodides, embedded in the polymer chain, have also been used as solvatochromic reporter molecules for the determination of microenvironment polarities in synthetic polymers [173]. No correlation was observed between Z values and the relative permittivity e, or functions thereof [317]. Measurement of solvent polarities using empirical parameters such as Z values has already found favour in textbooks for practical courses in physical organic chemistry [64]. 

The properties of the microenvironment of soluble and cross-linked synthetic polymers were studied using solvatochromic reporters bound to polymers. The polarity of the domain of polymer chains was estimated in one-component and binary solvents and compared with the polarity of solvents used. The polarity was expressed semiempirically by the absorption or emission band energy of a solvatochromic compound. The polarity of the microenvironment of soluble polymers and also the polarity in the vicinity of matrix of cross-linked polymers suspended in aqueous buffer was almost in all cases lower than that of the solvent. 

This chapter focuses on this particular family of photochromic systems. As presented elsewhere in this book, azobenzene-containing materials experience reorganizations at different length scales in response to light of the appropriate wavelength. The photochemistry of azobenzene molecules will be described. The main types of azobenzene polymeric architectures will be presented as well as associated synthetic methods. A brief overview of the photoresponse of azobenzene polymers when exposed to linearly polarized light in their absorption bands will be presented. Special emphasis will be... 

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