G. Floudas et al., Segmental and chain dynamics of polyisoprene in block copolymer/homopolymer blends. A dielectric spectroscopy study, MACROMOLEC, 32(22), 1999, pp. 7496-7503
The local and global dynamics of polyisoprene (PI) have been studied in a w
ell-defined restricted environment. The restriction is provided by the ther
modynamic field of segregated poly(styrene-b-isoprene) (SI) diblock copolym
ers. The copolymers were nearly symmetric in composition, and the amount of
added PI's was kept below 20% to ensure the absence of macrophase separati
on in the blends. Two studies have been made. In the first study, different
PI's with molecular weights in the range from 1.2 x 10(3) to 5.5 x 10(4) h
ave been added to a symmetric SI diblock copolymer. We found that both the
homopolymer and PI block dynamics are modified in the blends, and the degre
e of modification can be qualitatively accounted for by the reptation and a
rm-retraction mechanisms, respectively. A quantitative comparison, however,
would require an unrealistic increase of the entanglement molecular weight
. In addition, for the higher molecular weight homopolymers there is an eff
ect on the homopolymer chain dynamics due to the confinement within the cen
ter of the lamellae. In a second study, the same PI was inserted in differe
nt (symmetric) SI diblock copolymers with an increasing degree of segregati
on. We found a dynamic signature of the homopolymer localization imposed by
the thermodynamic field. Block copolymer/homopolymer blends are model syst
ems for studying the effect of confinement on the local and global dynamics
.