Local order and strain-induced orientation in poly(butadiene) networks studied by H-2 NMR

Deuterium nmr has been employed to determine the average orientation of cha in segment in poly(butadiene) networks. The nmr spectrum lineshape reveals the orientation distribution of network vectors due to the crosslinks, wher eas the observed splitting gives information about the orientation due to s egmental interactions. Both the lineshape and the splitting have been fitte d simultaneously for a range of deformed poly(butadiene) networks varied in crosslink density and precursor chain length. From the fitting parameters the separate contribution to the average orientation arising from network c onstraints and interaction are calculated. These are used to estimate the e ffective molecular weight between topological constraints and the size of t he segmental interaction. It could be shown that the latter remains constan t as the crosslink density is varied. This is a strong evidence of the rece ntly published theoretical framework.