Chemistry Reference
In-Depth Information
Figure 4.16 Phase diagram of poly(isoprene-b-2-vinylpyridine) with octyl gallate, indicating
the transition between different morphologies with octyl gallate content and temperature
(D, disordered; S, spherical; H, hexagonal; L, lamellar; L2, lamellar with reduced spacing; I, inter-
mediate state). Reprinted fromBondzic et al. (2004). Copyright 2004 American Chemical Society.
FTIR revealed that hydrogen bonding decreased with heating above 100 8C, so at
190 8C almost all of the pyridine groups were not hydrogen bonded.
Chao et al. (2004) studied the reversible attachment of liquid crystalline
side chains to poly(acrylic acid-b-styrene) block copolymers via hydrogen bonding
of imidazole groups to mesogens. The reversibility of the attachment of the meso-
gens, which tended to form smectic phases, was proposed to play an integral role
in the ability of these block copolymers to undergo reorientation of the lamella rela-
tive to external electrodes with an alternating electric field above the T
g
.Comparisons
with covalently bound chromophores showed that reorientation of the lamella did
not occur. Further studies involving poly(methacrylic acid-b-styrene) with imida-
zole containing mesogens allowed the fabrication of temperature-dependent photonic
bandgap materials that exhibited reflectivity maxima from 560 to 569 nm that reversibly
changed as a function of temperature from 40 to 70 8C(Osujietal.2002).
Recently, ten Brinke and Ikkala's group demonstrated the attachment of ionic
molecules (zinc dodecylbenzene sulfonate) to poly(styrene-b-4-vinylpyridine) via
coordination of the zinc ions to the pyridine rings (Valkama et al. 2003). These
blends possessed lamellar morphology, even at low weight fractions (0.23) of the 4-
vinylpyridine and zinc dodecylbenzene sulfonate, possibly due to the strength of the
ionic interactions. Strong segregation attributable to ionic interactions often leads to
altered morphology in ionomers (Mani et al. 1999). Although the crystallinity of the
zinc dodecylbenzene sulfonate was suppressed in the blends, lamellar packing
present in the pure salt was observed in the blends, indicating a lamella within
lamella structure. The zinc salt was selectively removed using methanol washes.
4.7. CONCLUSIONS AND SUMMARY
Hydrogen bonding interactions have gained significant attention recently as a means
of introducing novel, thermoreversible interactions to polymers, influencing both
