Modern Polymer Spect..

1.5 Appliccitioiis 23
Methylene
Figure 1-20. IR spectra of normal atactic polystyrene and
backbone-deuterated polystyrene films.
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hydrogen bonding, is often involved in such blends to overcome the tendency
to phase segregate. In those cases, 2D IR spectroscopy is especially suited for the
investigation of the molecular origin of such specific interactions. One of the wellknown
miscible systems, a blend of atactic polystyrene and poly(viny1 methyl ether)
1191. was investigated using 2D IR to elucidate the molecular origin of the miscibility
of these polymers [52. 531.
Interestingly. polystyrene and poly(viny1 methyl ether) are very different polymers.
Polystyrene is a hard hydrophobic plastic resin. while polyivinyl methyl ether)
is a soft water-soluble polymer. It is quite surprising that such a pair of polymers
could produce a molecularly mixed homogeneous one-phase system. The specific
origin of the miscibility of this polymer pair is not well understood, although some
level of interaction is speculated between the methoxyl groups of poly(viny1 methyl
ether) and the phenyl groups of polystyrene [54].
To simplify the spectral assignment, polystyrene which had been selectively
deuterium substituted to eliminate the backbone contribution (Figure 1-21) was
blended with poly(viny1 methyl ether). Special attention was paid to the symmetric
CHZ-stretching peak of the methoxyl group of the poly(viny1 methyl ether) component
near 2820 cm-'. Figure 1-22 shows the asynchronous 2D IR spectrum of
poly(viny1 methyl ether) in this region. The presence of a pair of asynchronous cross
peaks at the spectral coordinates at 2825 and 2813 cm-' indicates there are two
distinct populations of methoxyl groups belonging to the poly(viny1 methyl ether)
component of this blend, each having a different IR absorption band.
Figure 1-23 shows that the methoxyl band of poly(viny1 methyl ether) at
28 13 cm-' is synchronously correlated with the IR bands located at 3055 cm-' and
3024 cm-' (assigned to the phenyl side groups of the polystyrene component of this
blend). The presence of such synchronous correlation cross peaks strongly suggests
the existence of a specific interaction synchronizing the local motions of the
methoxyl groups of polyivinyl methyl ether) with the polystyrene phenyl groups.