Reações interfaciais de Poli(dimetilsiloxano)s com superficies hidroxiladas

AUTOR(ES)
DATA DE PUBLICAÇÃO

1997

RESUMO

Polysiloxanes, commonly know as silicones, are polymers formed by an Si-O backbone containing organic groups attached to the silicon atoms. Their chemistry is basically determined by the polarization of the Si-O bonds, and by the structure of the pendant organic groups. The Si-O bond is highly resistant to homolytic cleavage, but is susceptible to heterolytic cleavage, which makes the backbone sensible to attack by acids or bases. The susceptibility to acid or basic group attack enables silicones to undergo reactions with inorganic surfaces, especially at higher temperatures. In this work we have studied the reactivity of polydimethylsiloxane (PDMS), when heated in the presence of inorganic substrates. At temperatures above 200°C, PDMS shows a considerable increase in its chemical activity. Heating the polymer in the presence of inorganic surfaces leads to chemical reaction between the polymer and the surface, yielding a thin PDMS film covering the surface. This reaction has enabled us to develop a method for encapsulating inorganic particles, leading to composite powders wich consist of an inorganic core surrounded by a polymeric shell. We obtained composites with CaCO3, Fe2O3, AI2O3 and MgO. All of them present hydrophobic surfaces, with low wettability by polar solvents. TEM images show the presence of a dense and continuos film around the particles of Fe2O3/PDMS composite. PDMS-treated calcium carbonate adsorbs much less methylene blue, in relation to the non-treated salt. The infrared spectrum of the polymer linked to the particles presents the same absorption bands as the initial oil. The Si nuclear magnetic ressonance spectrum of PDMS-treated calcium carbonate shows a new chemical environment, with silicon atoms bound to three oxygen atoms. These results suggest that the polymer attached to the surface has a similar composition to that of the initial oil, however with some degree of crosslinking. The attached polymer is also stable towards hydrolysis and to removal by organic solvents.

ASSUNTO(S)

carbonato de calcio compositos polimericos silicones adesão

ACESSO AO ARTIGO

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