BULK AND SOLUTION PROPERTIES OF PEPTIDE-POLYMER CONJUGATES - Biologically-Responsive Hybrid Biomaterials - page 13

poly( ō -benzyloxycarbonyl- L -lysine) (PFS- b -PZLLys) and studied their self-
organization behavior in both the bulk state and in solution. In the bulk state, a
cylindrical in-lamellar structure was observed in a compositionally asymmetric
sample. Rod-like micelles with a polyferrocenylsilane core formed in a
polypeptide-selective solvent alone or in the presence of a common solvent.
2.2. Triblock copolymer architectures
Polydiene-based diblock copolymers
Whereas Gallot et al. have mainly studied the solid-state organization of PB-
based diblock copolymers, Nakajima et al. concentrated on ABA-type hybrid
block copolymers containing PB as the B component (“once-broken rods”). In a
first series of publications, the structure and properties of PBLG- b -PB- b -PBLG
triblock copolymers containing 7.5-32.5 mol % (= 3.0-14.3 vol %) PB were
investigated [33-35]. Infrared spectroscopy and WAXS experiments on films of
the triblock copolymers indicated that the PBLG blocks were predominantly α-
helical. From the WAXS experiments, it was concluded that the PBLG blocks
assembled into different structures, depending on the type of solvent that was
used to cast the films. In benzene cast films, the peptide helices were relatively
poorly ordered, similar to the so-called form A morphology of PBLG [36]. In
contrast, the PBLG segments in films cast from chloroform (CHCl 3 ) were well-
ordered and contained paracrystalline and mesomorphic regions. Based on TEM
analysis, a cylindrical microstructure was proposed for a triblock copolymer
containing 8 vol % PB. Interestingly, copolymers having the same composition
but polypeptide segments made of either enantiomerically pure or racemic γ-
benzyl glutamate exhibited not only different secondary structures (α-helix or
random coil, respectively; FTIR and WAXS), but also different supersturctures
(TEM). A cylindrical or lamellar morphology was proposed in the first case and
a more spherical superstructure in the second case [37].
The bulk and surface structure of solvent cast films from a series of PBLG- b -
PB- b -PBLG triblock copolymers with much higher PB contents (50-80 mol %)
than the samples discussed above have been discussed by Gallot et al. [38]
The organization of these copolymers was compared with that of three other
triblock copolymers with approximately the same PB content (~50 mol %) but
which were composed of poly( N ε -trifluoroacetyl L -lysine) (PTLLys), poly( N 5 -
hydroxyethyl L -glutamine) (PHLGln) or polysarcosine (PSar) as the peptide
block. For any sample investigated, x-ray scattering experiments indicated a
hexagonal-in-lamellar bulk morphology. X-ray photoelectron spectroscopy