CHAIN DYNAMICS IN CORONAS OF IONOMER AGGREGATES

Chain dynamics in coronas of ionomer aggregates, or the areas surrounding the ionic cores, is reported at the segmental level for poly(styrene-b-sodium acrylate) reverse micelles and for sodium carboxylate terminated polystyrene aggregates in CCl4, on the basis of H-2 NMR measurements. In the synthesis of the ionomers, a short H-2-labeled styrene block (ca. 3 units) was incorporated into each polystyrene chain. The distances between the H-2-labeled segments and the ionic cores were controlled by the number of styrene units separating the H-2-labeled segments from the nonionic-ionic block junctions. NMR line width, signal intensity, and relaxation times of the block ionomers and their nonionic precursors clearly indicate that the mobility of the soluble segments near the ionic cores is reduced dramatically. At a distance of 25 repeat units from the nonionic-ionic block junctions, the mobility is still significantly lower than that in single chains, while at a distance of 50 repeat units from the nonionic-ionic block junction, the mobility is essentially the same as that in the single chains. Even for sodium carboxylate terminated polystyrene, where there is only a single ionic group, the H-2-labeled styrene segments 14 repeat units away from the nonionic-ionic block junction are still subject to the restriction in mobility imposed by the ionic association, H-2-labeled ionomers with the same styrene block but different lengths of ionic blocks were also examined; it was found that the longer the ionic block, the slower the motion in the coronas, but the effect becomes less dependent on the ionic block length when the ionic blocks are longer than 6 repeat units. Relaxation data were also obtained at three frequencies (76.75, 46.05, and 30.7 MHz) and at multiple temperatures for (PS)(92)-b-(PS-d(8))(4.5)-b-(PS)(17)-b-(PANa)(15) and interpreted by use of the log chi(2) distribution model. The results of the present study support the recently proposed restricted mobility model by Eisenberg, Hird, and Moore for random ionomers, assuming that the effect of ionic association on chain dynamics in polymer melt and in polymer solution is similar in trend.