BULK AND SOLUTION PROPERTIES OF PEPTIDE-POLYMER CONJUGATES - Biologically-Responsive Hybrid Biomaterials - page 8

[21]. To this end, a series of five diblock copolymers was prepared from an
identical ω-amino-polystyrene macroinitiator ( P n = 52; polydispersity index, PDI
= 1.03). The peptide content in these diblock copolymers varied between 0.43
and 0.68 and the PDI ranged from 1.03 to 1.64. Evaluation of the SAXS data
with the interface distribution function and the curvature-interface formalism
confirmed, as expected, the hexagonal-in-undulated (or zigzag) lamellar solid-
state morphology. Fractionation of the peptide helices according to their length
leads (locally) to the formation of a nearly planar, parallel lamellar interface,
which is disrupted by kinks (undulations).
Reiter and Schlaad et al. [22] used atomic force microscopy (AFM) to
investigate the formation of hierarchical structures of PS 52 - b -PBLG 104 in thin
films. Thin films with a thickness of ~4 and 40 nm were prepared by spin-coating
of dilute polymer solutions on silicon substrates and were subsequently annealed
in saturated tetrahydrofuran (THF) vapor to achieve a controlled crystallization
of the α-helical PBLG. On the smallest length-scale, the structure was found to
be built of short ribbons or lamellae of interdigitated polymer chains. PBLG
helices were fully stretched in thin films, in contrast to what has been observed in
the 3D organized bulk mesophase (see above). Depending on the time of solvent
annealing, different ordered structures on the micrometer length-scale could be
observed (Figure 4).
The examples discussed so far all involved relatively high molecular weight
diblock copolymers. In this case, the molecular weight of the polypeptide block
is usually sufficiently high so that it forms a stable α-helix and the common
hexagonal-in-lamellar morphology is found. The situation changes, however,
when the molecular weight of the block copolymers is significantly decreased.
The influence of molecular weight on the solid-state organization of polystyrene-

(a) (b) (c)

Fig. 4. AFM height images of a film of PS 52 - b -PBLG 104 obtained by spin-coating from a 5 mg/mL
THF solution and subsequent exposure to saturated THF vapor for 3.5 (a), 22.5 (b), and 42 hours
(c). Adapted from [22].