FURAN-CONTAINING MODIFIED ORGANOSILICON POLYMERS - PREPARATION, PROPERTIES AND SOME APPLICATIONS

Oligoethoxysiloxanes (OES) have been prepared by partial hydrolytic po lycondensation 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 co ncentration of the catalyst (HCl) have been established. OES were used as initial materials for the preparation of a new kind of polymer-oli gofurfuryloxysiloxanes (OFS). OFS with different degrees of polyconden sation and substitution were obtained by transesterification of OES wi th furfuryl alcohol in the presence of nucleophilic catalysts, mainly fluorides of alkali metals. The oligomers have been characterized by v iscosity measurements, elemental analysis. IR and H-1-NMR spectroscopi es. Cross-linked polyfurfurylsiloxanes (PFS) were obtained by thermal or catalytic polymerisation of the OFS. The thermal stability of the p olymers, as estimated by TGA analysis, increased with increasing degre e of polycondensation and substitution in the initial OFS. PFS with th e highest degree of polycondensation were stable up to 450 degrees C i n air. Highly-filled composites based on OFS were prepared by simple m oulding under ambient temperatures, followed by a post-cure at 70 degr ees C. Lewis acids (FeCl3, SnCl2) were also used as catalysts for the polymerisation. PFS composites have shown excellent mechanical propert ies, as well as heat resistance and resistance to attack by corrosive media. (C) 1997 Elsevier Science Ltd.