DIRECT NMR EVIDENCE FOR A LOCAL RESTRICTION IN THE SEGMENTAL CHAIN MOBILITY OF A MODEL IONOMER

To probe the local mobility of the chain segments directly attached to ionic multiplets, two model ionomers have been synthesized. The first one is a carboxylato-telechelic deuterated polystyrene in which the c hain segments bearing the sodium carboxylate end groups have been sele ctively protonated; the second one has a protonated polystyrene backbo ne terminated at both ends with a deuterated polystyrene segment beari ng the sodium carboxylate groups. Both polymers have been studied by h igh-resolution solid-state C-13 NMR. Line-width measurements of the pr otonated units have clearly shown that the dipolar interactions of the sodium carboxylate end groups are responsible for a mobility restrict ion of the chain end segments. This experiment is thought to be the fi rst direct evidence for the model recently proposed by Eisenberg et al . for ionomer morphology according to which the ionic multiplets are s urrounded with a shell of constrained polymer segments.