Estudo das relaxações de polimeros utilizando sondas luminescentes

AUTOR(ES)
DATA DE PUBLICAÇÃO

1988

RESUMO

Some relaxations of organic polymers were studied using luminescence probes dispersed in the polymers. We have studied the following polymers: poly(styrene), poly(vinyl acetate), poly(propylene), low density poly(ethylene) and poly(ethylene glycol)-600. Anthracene and benzophenone were dispersed in these polymers to analyse the temperature dependence on both fluorescence and phosforescence emissions. Therefore, it was necessary to make a search of the photophysical properties of these probes in the polymers, as: kind of emission, change of photophysical processes resulting from the interactions with the polymers and formation of aggregates in the matrices. The studies of the temperature dependence on the fluorescence intensity of the anthrance dispersed in the these polymers, allowed us to determine the glass relaxation (glass transition) temperature of poly(ethylene glycol)-600, which is associated with micro-brownian movement of about 50 methylenic units of the polymer chain. This relaxation could be observed due to the difference of the photophysical processes of monomeric and crystal anthracene, since the latter is formed after the relaxation. The relaxations that include the movement of small groups of these polymers, was not observed using this fluorescence probe molecule. These relaxations were observed by the dependence on phosforenscence intensity of the benzophenone dispersed in these phosforescence intensity of the benzophenone dispersed in these polymers. This process is characterized by the decresse of phosforescence intensity in the temperature range of relaxation, indicate changes in the photophysical properties of the probe molecule. The mechanism of these changes was studied and may envolve a desativation by exciples formation (ralaxation in poly(styrene)) and/or by collision between molecular oxigen and the probe molecule(all polymers). The following results were obtained: determinationh of the relaxation temperature for: (a) rotation of phenyl groups of the poly(styrene) (g relaxation); (b) rotation of the methoxil groups copolimerized as impurities of the poly(vinyl acetate); (c) reorientation of the methyl groups of the poly(propylene); (d) rotation of some methylenic units of the chain of poly(ethylene) (g relaxation); (e) and the g relaxation in poly(ethylene glycol)-600, that envolves the movement of 3 to 4 methylenic groups of the main chain.

ASSUNTO(S)

polimeros - testes sardas (instrumentos eletronicos)

ACESSO AO ARTIGO

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