UNIAXIALITY INDUCED IN A STRAINED POLY(DIMETHYLSILOXANE) NETWORK

The orientational order generated in a uniaxially strained polymer network is described and discussed. Experiments have been performed on an end-linked poly(dimethylsiloxane) network, using the deuterium nuclear magnetic resonance technique (2H NMR). We first recall that the resonance spectra observed in the absence of an external force reflect a local anisotropy of segmental motions, which may be related to the constraints associated with the presence of network junctions. When a uniaxial force is applied, a detailed analysis of the spectrum shows that the segmental motions become uniaxial around the external force direction. This experimental fact, which is inconsistent with noninteracting chain descriptions, is interpreted as new evidence for short-range orientational interactions between segments (introduced previously by Sotta et al. to account for free-chain orientation). A crude mean-field treatment including these interactions, together with the constraints associated to junctions, is proposed and compared with experiments. © 1990, American Chemical Society. All rights reserved.