DEUTERIUM NMR LINESHAPES IN POLYMER NETWORKS

The deuterium NMR lineshapes in poly(dimethyl siloxane)-d6 networks may be quantitatively simulated. The inferred microscopic reorientational processes that the chain segments exercise average the quadrupolar interaction and are indicative of either dynamic heterogeneity (a distribution of segmental reorientation rates that differentially average a single-valued, static, residual quadrupolar interaction) or static heterogeneity (a distribution of intrasegment, pre-averaged, static interactions that are further averaged by a single rate process). In this paper, the static heterogeneity model, where ultrafast motional pre-averaging within chains segments leads to partially averaged quadrupolar interactions that are subsequently averaged by the slower chain dynamics is investigated. In this model differential pre-averaging, unlike the dynamical heterogeneity, does not require distinct segmental domains that are characterized by different rotational correlation times; one need only have intrasegmental differences that could, in principle, exist within a single chain. Under uniaxial extension, the fluid network is similar to an anisotropic liquid having macroscopically homogeneous (nematic-like) segmental orientational order that is characterized by a single order parameter for the Si-CD3 bond.