Damping Elastomer Based on Model Irregular Networks of End-Linked Poly(Dimethylsiloxane)

We demonstrate a silicone damping elastomer with a constant high damping performance (tan = Eʹ ʹ\Eʹ 0.3 where Eʹ and Eʹ ʹ are the storage and loss Youngʹs moduli, respectively) over a broad temperature range of 180 C (-30 C < T < 150 C) utilizing a slow viscoelastic relaxation of an irregular network structure with many pendant chains. In addition to tan , (theta)Eʹ is almost unaltered in the corresponding temperature range. These are in contrast to the markedly temperature-dependent damping and modulus of conventional damping elastomers using the glass transition as the energy dissipation. The temperatureand frequency-insensitive damping and elasticity are of significance to extend the availability in the industrial uses. The irregular networks have been prepared by end-linking a mixture of bi- and monofunctional end-reactive precursor linear poly (dimethylsiloxane) (PDMS) chains with trifunctional cross-linker, or end-linking the bifunctional precursor chains with trifunctional cross-linker at off-stoichiometric ratios. Independently of mechanical testing, the fractions of pendant (Wpen) and elastic chains (Wel) in the irregular networks have been evaluated using a nonlinear polymerization model. It has been demonstrated that tan increases with increasing Wpen; the pendant chain whose one end is free to move significantly contributes to the dissipation of deformation energy via the viscoelastic relaxation. The temperature- and frequency-insensitive damping originates from a broad relaxation spectrum of the irregular networks comprising the pendant branched chains with various shapes and a wide size distribution