Tearing energies for in-situ reinforced poly(dimethylsiloxane) networks

Tetraethoxysilane was used to end-link functionaIly-terminated poly(dimethy l-siloxane) chains, and then to serve as the source of reinforcing silica p articles upon its hydrolysis and condensation within the elastomeric networ ks. These in-situ filled elastomers were characterized using transmission e lectron microscopy, thermogravimetric analysis, and tearing energy measurem ents. The electron micrographs showed the presence of well-dispersed, unagg lomerated silica particles with average diameters rather narrowly distribut ed over the range 150-250 Angstrom. These reinforcing particles were found to improve the thermal properties of the networks. Specifically, the larger the amount of filler thus incorporated, the higher the onset degradation t emperature, and the larger the weight residue at 800 degrees C. Effects wer e also found with regard to the tearing measurements, with the filled mater ials showing unstable tearing (stick-slip tearing), particularly at higher tearing rates. In contrast, the unfilled materials showed steady tearing. T he tearing energies of the filled materials were significantly larger than those of the unfilled material. A marked increase in the tear strength occu rred upon increasing the silica content up to 10 wt.%, followed by smaller improvements with additional increases in silica content. (C) 2000 Elsevier Science S.A. All rights reserved.