Study of reactions involved in photodegradation of dyed polymers

• Grant number: 05/05175-7
• Support Opportunities: Scholarships in Brazil - Post-Doctoral
• Start date: January 01, 2007
• End date: September 19, 2009
• Field of knowledge: Physical Sciences and Mathematics - Chemistry - Organic Chemistry
• Principal Investigator: Miguel Guillermo Neumann
• Grantee: Beatriz Eleutério Goi Carvalho
• Host Institution: Instituto de Química de São Carlos (IQSC). Universidade de São Paulo (USP). São Carlos , SP, Brazil

Abstract

The knowledge of the mechanisms of photodegradation of dyed polymers is of great scientific interest, due to the possibility to enhance the useful life of those materials. These studies involve the presence of dyes, or other cromophores, in the polymeric material, that can be bonded covalently to the polymeric chains or added afterwards. The effect of the UV irradiation on polyacrylates is very well-known: scission of the side-chain and formation of radicals, but they are few reports in the literature that deal with the photodecomposition of polymethacrylates in the presence of dyes.In the present project four polymers will be used: poly(methyl methacrylate), poly(ethyl methacrylate), poly(n-butyl methacrylate) and poly(n-hexyl methacrylate). The effect of the size of the alkyl groups on the ester on the photodegradation mechanism of the polymer will be evaluated. The dyes that will be used as photosensitizers are benzophenone and several substituted thioxanthones. Some of the thioxanthones, that bear a vinyl group will be incorporated covalently to the polymethacrylate chain. The polymer films, used in the experiments of photodegradation, will be irradiated with visible or UV light. The photodegradation kinetics will be determined by using FTIR and UV-Vis techniques. The molecular weight of the polymetacrylates will be analyzed by GPC.The elemental reactions involved in the global process will be studied by laser flash photolysis, and static and dynamic fluorescence. Model molecules, such as dimethyl-2,2-dimethyl glutamate and squalene, will be used in these studies in order to mimic the polymer structure or its viscosity. Therefore, the present project represents a contribution to the study of the photochemistry of polymers and to polymer science.