Solid state ²H-NMR studies of segmental dynamics in polymer blends

Abstract

Recent two-dimensional (2D) ²H-NMR studies on nearly ideal mixtures are reviewed. The use of selective deuterium labeling allows the unambiguous observation of the individual segmental dynamics of each component in the blend. 2D exchange spectra provide both the mean motional rates and the motional distributions, which was necessary to discriminate among the disparate explanations of blend behavior. The components exhibit very 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 heterogeneities. The individual mean motional rates are used to define distinct glass transition temperatures, T_(g,i)* for each species, i. The separation between the T_(g,i)*,s of the two species increases with the content of the high-T_g component. The widths of their individual motional distributions also increase with the content of the high-T_g component. These two effects combine to produce the increase in both the anomalously broad glass transition and the thermorheological complexity of these blends with fraction of the high-T_g component.