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 delta = E/E' approximate to 0.3 where E' and E are the storage and loss Young's moduli, respectively) over a broad temperature range of 180 degreesC (-30 degreesC < T < 150 degreesC) utilizing a slow viscoelastic relaxation of an irregular network structure with many pendant chains. In addition to tan delta, E' 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 temperature- and 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 (W-pen) and elastic chains (W-el) in the irregular networks have been evaluated using a nonlinear polymerization model. It has been demonstrated that tan delta increases with increasing W-pen 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.