By Jan F. Rabek
In this ebook on actual features and sensible features of polymer photodegradation Rabek emphasizes the experimental paintings at the topic. crucial characteristic of the booklet is the actual interpretation of polymer degradation, e.g. mechanism of UV/light absorption, formation of excited states, strength move mechanism, kinetics, dependence on actual homes of macromolecules and polymer matrices, formation of mechanical defects, practics in the course of environmental growing old. He comprises additionally a few points of polymer photodegradation in environmental and house condition.
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74) where R is the distance the excitation travels per hop, [D] is the concentration of donor, and kM is the rate constant of energy migration by excitation hopping. For styrene-co-vinylbenzophenone, up to 103 jumps of the triplet energy migration from benzophenone to benzophenone is indicated. Considering that r is the distance of net molecular energy migration, and RO(DD) is the critical transfer distance for which the probability of energy transfer (between D* and D) equals the probabilitty of deactivation of D* by all other processes, two extreme situations in energy migration may occur.
This can lead to the "internal filter phenomenon", registered as a serious distortion of the emission spectrum of donor. e. their centres are separated by the sum of their molecular radii. Their electron clouds may overlap each other and an electron on D* may also appear on A [200]. 8) CD (v)dv = 1 , 00 and v is the wavenumber (em-I). 9) FD(V)CA(V)dv is a measure of the overlap of the donor emission and acceptor absorption. 13) (triplet-triplet annihilation). The triplet-triplet energy transfer, which is forbidden €*+) by the resonance-excitation energy transfer is allowed by an electron exchange energy transfer: 3D*(triplet) + A ""*' D + 3A* (triplet) .
First, both degradation and crosslinking take place predominantly in the amorphous part of the material. All radiation-induced processes start at specifically radiation sensitive sites (chromophoric groups) in the polymeric material. Therefore both chain scission and crosslinking are not introduced randomly. It is generally accepted that the photo-oxidation processes are initiated at the surface, which gives rise to gradient of deteriorated material across the specimen thickness (cf. Sect. 12).