Ra. Vaia et al., RELAXATIONS OF CONFINED CHAINS IN POLYMER NANOCOMPOSITES - GLASS-TRANSITION PROPERTIES OF POLY(ETHYLENE OXIDE) INTERCALATED IN MONTMORILLONITE, Journal of polymer science. Part B, Polymer physics, 35(1), 1997, pp. 59-67
The relaxation behavior of poly( ethylene oxide) (PEG), intercalated i
n montmorillonite, a naturally occurring mica-type silicate, was studi
ed by differential scanning calorimetry (DSC) and thermally stimulated
dielectric depolarization(or thermally stimulated current, TSC). The
materials were synthesized by melt or solution-mediated intercalation.
In both intercalates, the PEO chains were confined to ca. 0.8-nm gall
eries between the silicate layers. The solution intercalate contained
a fraction of unintercalated PEO chains which exhibited a weak and dep
ressed PEO melting endotherm in DSC. In contrast, the melt intercalate
was ''starved'' such that almost all the PEO chains were effectively
intercalated. For these melt intercalates, no thermal events were dete
cted by DSC. TSC thermal sampling technique was used to examine the gl
ass transition regions and to estimate the extent of cooperativity of
chain motions. The motions of the intercalated PEO chains are inherent
ly noncooperative relative to the cooperative T-g motions in the amorp
hous portion of the bulk polymer. This is presumably due to the strong
confining effect of the silicate layers on the relaxations of the int
ercalated polymer. (C) 1997 John Wiley & Sons, Inc.