POLY 338 |
| Bimodal elastomers were prepared from functionally-terminated poly(dimethylsiloxane), using mixtures of very long chains with some nearly monodisperse chains that were significantly shorter than those previously used in such networks. The Mooney-Rivlin stress-strain plots of these elastomers in elongation generally showed three regimes. In the first, the modulus was abnormally large, possibly due to some deformations of the numerous very short chains. In the second regime, the elastomers acted like network with high-functionality cross links (possibly due to clustering of junctions). In the third, the modulus shows large upturns resulting from the limited chain extensibilities of the very short chains. Some swelling and birefringence data correspond most closely to Regime II behavior. Some aspects of the rubber elasticity results are similar to network properties sometimes attributed to entanglements. Birefringence measurements indicate that there are Gaussian and non-Gaussian aspects of these elastomers. |
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Silicones and Silicone-Modified Materials
8:30 AM-12:00 PM, Tuesday, 12 September 2006 San Francisco Marriott -- Salon A2, Oral
Division of Polymer Chemistry |