BULK AND SOLUTION PROPERTIES OF PEPTIDE-POLYMER CONJUGATES - Biologically-Responsive Hybrid Biomaterials - page 6

Fig. 2. Schematic model representation of the hexagonal in hexagonal (HH) morphology obtained
for PI 49 - b -PZLLys 178 copolymer cast from dioxane solution. Adapted from [16].
PZLLys 61 and PI 49 - b -PZLLys 92 , the x-ray scattering data were in agreement with
a hexagonal-in-lamellar morphology. Interestingly, for PI 49 - b -PZLLys 123 and
PI 49 - b -PZLLys 178 a hexagonal-in-hexagonal structure was found. This
morphology is illustrated in Figure 2. This structure is unprecedented for
polydiene-based peptide hybrid block copolymers, but has also been found
for low molecular weight polystyrene- block -poly( ȳ -benzyl L -glutamate) (PS- b -
PBLG) copolymers [17].
Polystyrene-based diblock copolymers
In an early study, Gallot et al. [13] reported on the bulk nanoscale structure of
PS- b -PZLLys diblock copolymers, which were based on a PS block with a
number-average molecular weight of M n = 37 kg/mol and had peptide contents
ranging from 18-80 mol %. X-ray scattering patterns of dry samples following
evaporation from dioxane showed two sets of signals, characteristic again of a
hexagonal-in-lamellar superstructure. For several samples, the calculated length
of the peptide helix was larger than the peptide layer thickness as determined
from the x-ray data. In these cases, it was proposed that the helical PZLLys
chains were folded in the peptide layer. Thus, the bulk nanoscale structure of the
PS- b -PZLLys copolymers can be described in terms of the same hexagonal-in-
lamellar model as it was also proposed for the PB-based block copolymer
described earlier (Figure 3).
Along the same lines, Douy and Gallot [15] also studied the bulk nanoscale
organization of PS- b -PBLG. For block copolymers composed of a PS block with