Contributions to the total orientation of deformed elastomers arising fromthe network structure and chain interactions as measured by NMR

Deuterium NMR has been employed to determine the average orientation <(P-2( cos theta))over bar> of chain segments in poly(butadiene) networks. It is s hown that the free induction decay separates the contribution to the orient ation arising from the network constraint to that from chain interactions. The NMR spectrum line shape reveals the orientational distribution of netwo rk vectors due to the crosslinks, whereas the observed splitting gives info rmation about the orientation due to segmental interactions. Both the line shape and splitting have been fitted simultaneously for a range of deformed poly(butadiene) networks. From the fitting parameters, the separate contri butions to the average orientation of the chain segments arising from the n etwork constraint and from the interactions are calculated. These in turn a re used to determine the molecular weight between cross-links and the size of the segmental interactions, which we choose to express in terms of the E dwards' screening length. This work is also important to computer modeling of the stress-optical coefficient where the interchain interactions are ign ored.