Sintese e algumas propriedades de oligo e polissilarilenos

AUTOR(ES)
DATA DE PUBLICAÇÃO

1991

RESUMO

In this work several oligo- and poli-p-silphenylenes containing SiMe2 or SiPh2 groups, alternated whith p-phenylenes units in the main chain, were synthetized. The olygomers and polymers were sinthetized from organic substrates with varied reactivities and solvents with different coordination ability via di-Gignard intermidiates. Poly-p-silphenylenes was also prepared by Wurtz-type coupling reaction of 1,4 Me2Si(C6H4CI)2 and Me2SiCl2 with metallic sodium in toluene. The results obtained have discussed in terms of the synthesis parameters. The products were characterized by infra-red spectroscopy and proton and carbon-13 nuclear magnetic resonance. The number average molecular weigth (Mn) for the oligo and polymers was determined by vapour pressure osmometry. The reactions using THF as solvent produced low number average molecular weigth oligomers (Mn 800 g/mol) which contained inserted fragments in the main chain. The products obtained when Et2O was used as solvent, displayed higher Mn values ( 1400 g/mol) and solvent insertion in the chain was not observed. In relation to the reactivities of organic substrates it was observed that the products obtained from 1,4-dichlorobenzene presented lower Mn than the ones prepared from 1,4-dibromobenzene. The products synthetized from Wurtz-type coupling reaction, showed higher number average molecular weigth than the ones obtained from Grignard reactants, also they exhibited fragments with Si-Si bond in the main chain. Absorption and emission electronic spectra in UV-vis region for all oligomers and polymers were also measured. They were compared to molecular p-silphenylenes type compounds previously prepared, which represented essential bilding units of the main chain. These studies showed that there is a perturbation of benzene LUMO levels by SiR2 groups. This analysis was reinforced by the comparison of the oligomers electronic behaviour with the ones from derivatives of 9,10-dibromoanthracene and R2SiCI2 also prepared in this project. As expected, no significant perturbation of the anthracene LUMO by SiR2 groups was observed. The majority of the products obtained are excellent absorbers, emitters and photostable species in the UV region. The thermal behaviour of to the SiMe2 derivatives according to thermogravimetric analysis, presented a tendency of increasing thermal stability with the number average molecular weigth. The same tendency was observed with decreasing in the percentage of THF insertion in the polymeric chain. The thermal behaviour of some compounds was studied by differential scanning calorimetry and showed endsothermal transitions whitin -140 to 30°C related to glass transition.

ASSUNTO(S)

polimeros e polimerização espectroscopia de absorção atomica

ACESSO AO ARTIGO

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