Segmental order in uniaxially strained bimodal polymer networks: a deuterium-NMR study

The segmental orientational order generated in bimodal poly(dimethylsiloxane) networks under uniaxial stress is probed using deuterium nuclear magnetic resonance ($^{2}$H-NMR). The induced segmental order is measured either on “short” chains ($M_{\rm n} = 3000$ g/mol) or on “long” chains ($M_{\rm n} = 25000$ g/mol). The segmental orientation is very similar for both kinds of chains and decreases linearly as the volume fraction $\Phi_{\rm L}$ of “long” chain increases. A mean field analysis including orientational correlations between segments is developed and accounts for these observations. Additionally, this study has been carried out on two sets of samples with different crosslinkers. It shows clearly that the induced orientational order depends on the nature of the crosslinking junctions