Comparisons between poly(dimethylsiloxane) networks filled with particles of poly(dimethylsiloxane) thermosets and unfilled bimodal networks prepared from the same components

Summary

Very short, non-elastomeric chains of poly(dimethylsiloxane) (PDMS) were incorporated in samples of a long-chain PDMS elastomer in two ways: (i) end linking the short chains into a thermoset, cryoscopically grinding it into fine particles, and then mixing them into much longer PDMS chains which were then also end linked, and (ii) end linking mixtures of the short and long chains simultaneously. The short chains introduced by the first method do give some increases in ultimate strength, but these increases are more than offset by decreases in maximum extensibility and the resulting filled elastomers are very weak. On the other hand, end linking the short chains directly into the longchain network gives much larger increases in ultimate strength and smaller decreases in maximum extensibility; as a result these bimodal elastomers are much tougher than the corresponding filled networks.