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| Author(s): |
Leticia Felipe Abdias Pinto
Total Authors: 1
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| Document type: | Master's Dissertation |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT) |
| Defense date: | 2009-04-07 |
| Examining board members: |
Carla Cristina Schmitt Cavalheiro;
Rose Maria Carlos;
Márcio José Tiera
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| Advisor: | Carla Cristina Schmitt Cavalheiro |
| Abstract | |
Many ketones, quinones and peroxides are initiators of different reactions such as polymerization, degradation, chemical modification that occur in organic compounds. Thioxanthone (TX) and Benzophenone (BP) are ketones often used as photosensitizers in photochemical reactions. The degradation of polystyrene films containing TX and BP was investigated. Films were irradiated at λ > 350 nmin different conditions at different times. The changes were investigated by infrared and UV-Vis spectroscopies and the molecular weight were determined by gel permeation chromatography (GPC). The UV-Vis spectra showed that TX is photobleached after 5 h, unlike BP which is photostable. Simultaneously, polymers containing chromoforic groups are formed and the light is absorbed by them. The formation of photoproducts films containing TX and BP showed an increase of absorbance between 280-360 nm and 310-370 nm, respectively. The IR peaks around 3645 and 1740 cm-1 indicated the generation of hydroperoxide and carbonyl species, respectively. The results showed that thioxanthone has generated more photoproducts than benzophenone. The UV-Vis irradiation of PS films in both samples presented a decrease in the molecular weight after irradiation, indicating that polymer chain scission occurs. The photophysics of the excited states of thioxanthone (TX) and thioxanthone which was chemically incorporated in polystyrene (PS-TX I and PS-TX II) have been studied in order to be able to predict their behavior as photoinitiator in photodegradation of PS. The triplet-triplet (TT) and transient absorptions of thioxanthone and thioxanthone-containing polystyrene (PS-TX I and PS-TX II) has been studied in different solvents in order to ascertain the effect of the solvent. A good correlation is found between the solvent ET(30) parameter and the energy of the triplet-triplet. The quenching rate constants for the deactivation of triplet thioxanthone by triethanolamine decreases when the solvent polarity increases. This variation is represented by the π*, α and β scale of solvent polarity. (AU) | |