SOLID-STATE H-2-NMR STUDIES OF SEGMENTAL DYNAMICS IN POLYMER BLENDS

Recent two-dimensional (2D) H-2-NMR studies on nearly ideal mixtures a re reviewed. The use of selective deuterium labeling allows the unambi guous observation of the individual segmental dynamics of each compone nt in the blend. 2D exchange spectra provide both the mean motional ra tes and the motional distributions, which was necessary to discriminat e among the disparate explanations of blend behavior. The components e xhibit vary different mean mobilities and broad mobility distributions near the glass transition. The broad macroscopic glass transition in the blends is attributed to both these two kinds of dynamic heterogene ities. The individual mean motional rates are used to define distinct glass transition temperatures, T-g,T-i for each species, i. The separ ation between the T-g,T-is of the two species increases with the cont ent of the high-T-g component. The widths of their individual motional distributions also increase with the content of the high-T-g componen t. These two effects combine to produce the increase in both the anoma lously broad glass transition and the thermorheological complexity of these blends with fi-action of the high-T-g component. (C) 1998 Elsevi er Science B.V. All rights reserved.