Furan-containing modified organosilicon polymers: Preparation, properties and some applications

Oligoethoxysiloxanes (OES) have been prepared by partial hydrolytic polycondensation of tetraethoxysilane (TES) with molar ratio n=[H2O](6):[{TES}(0)=0.2-1.5. The dependence of the composition and the structure of the OES on the value of n, the duration of the reaction and the concentration of the catalyst (HCl) have been established. OES were used as initial materials for the preparation of a new kind of polymer-oligofurfuryloxysiloxanes (OFS). OFS with different degrees of polycondensation and substitution were obtained by transesterification of OES with furfuryl alcohol in the presence of nucleophilic catalysts, mainly fluorides of alkali metals. The oligomers have been characterized by viscosity measurements, elemental analysis. IR and H-1-NMR spectroscopies. Cross-linked polyfurfurylsiloxanes (PFS) were obtained by thermal or catalytic polymerisation of the OFS. The thermal stability of the polymers, as estimated by TGA analysis, increased with increasing degree of polycondensation and substitution in the initial OFS. PFS with the highest degree of polycondensation were stable up to 450 degrees C in air. Highly-filled composites based on OFS were prepared by simple moulding under ambient temperatures, followed by a post-cure at 70 degrees C. Lewis acids (FeCl3, SnCl2) were also used as catalysts for the polymerisation. PFS composites have shown excellent mechanical properties, as well as heat resistance and resistance to attack by corrosive media. (C) 1997 Elsevier Science Ltd.