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27.2 Solution Self-assembly of Polypeptide-based Block Copolymers 839

length of the PLLys segment. A conclusive explanation of this unexpected aggrega-

tion behavior could not be given.

Core - forming Polypeptides Aggregates with an insoluble polypeptide core have

been prepared with block or random copolymers having linear or branched archi-

tecture. Most studies focused on aqueous systems (designated for use as drug

carriers in biomedical applications), and the only inverse systems investigated to

date are PB - b - PLGlu in dilute tetrahydrofuran (THF) and CH

solution and

PS - b - PZLLys in CCl

Harada and Kataoka [38 – 40] were the ﬁ rst to investigate the formation of polyion

complex (PIC) micelles in an aqueous milieu from a pair of oppositely charged

linear polypeptide block copolymers, namely of PEG

113

- b - PAsp

18,78

polyanions and

PEG

113

- b - PLLys

18,78

polycations [PEG = poly(ethylene glycol)]. Complexation studies

were carried out at pH 7.29, where both block copolymers had the same degree

of ionization ( α = 0.967) and were thus double - hydrophilic in nature and did not

form aggregates in water. Mixing of the copolymers at a 1 : 1 ratio of amino acid

residues resulted in the formation of stable and monodispersed spherical core -

shell assemblies of 30 nm in diameter (DLS). Another interesting feature con-

nected with PIC micelles is that of “ chain - length recognition ” [40] . PIC micelles

are exclusively formed by matched pairs of chains with the same block lengths of

polyanions and polycations, even in mixtures with different block lengths. The key

determinants in this recognition process are considered to be the strict phase

separation between the PIC core and the PEO corona, requiring regular alignment

of the molecular junctions at the core – corona interface, and the charge stoichiom-

etry (neutralization).

Yonese and coworkers [41] studied the aggregation behavior of PEG

113

- b -

PMLGlu

20,50

and lactose - modiﬁ ed PEG

- b - PMLGlu

in water. As shown by DLS,

the copolymers formed large aggregates with a hydrodynamic radius of R

≈ 250 nm.

Contrary to what was claimed by these workers, it seems more likely that these

aggregates were vesicles rather than spherical micelles. Key in the aggregation

behavior might be the association of α - helical PMLGlu segments, as evidenced by

CD spectroscopy, promoting the formation of plane bi - layers which then close into

vesicles [15] . Further systematic studies on this system and detailed analysis of

structures are lacking.

Closely related to this system are PEO

272

- b - PBLGlu

38 – 418

and PNIPAAm

203

- b -

PBLGlu

39 – 123

[PEO = poly(ethylene oxide), PNIPAAm = poly( N - isopropylacryla-

mide)] described by Cho and coworkers [42, 43] . The aqueous polymer solutions,

prepared by the dialysis of organic solutions against water, contained large spheri-

cal aggregates ( R

≈ 250 nm) with a broad size distribution (DLS). Although the

size suggested a vesicular structure of the aggregates, aggregation numbers

( Z < 100, method of determination not speciﬁ ed) were far below the values of

several thousands typically being reported for polymer vesicles [18] . It is also worth

noting that the PNIPAAm chains exhibit LCST (lower critical solution tempera-

ture) behavior. However, raising the temperature to the LCST ( ≈ 34 ° C) had no

serious impact on the size of the aggregates.

840 27 Self-assembly of Linear Polypeptide-based Block Copolymers

Dong and coworkers described symmetric triblock copolymers with a glyco

methacrylate middle block and two outer poly( l - alanine) (PLAla) or PBLGlu blocks

[44, 45] . The aggregates formed in dilute aqueous solution were spherical in shape

and were 200 – 700 nm in diameter (TEM). TEM further revealed a compact struc-

ture of the aggregates as with multi - lamellar vesicles. The dimensions of the

particles, however, were found to decrease with increasing concentration of the

copolymer.

Naka et al. [46] studied the aggregation behavior of poly(acetyliminoethylene) -

block - poly( l - phenylalanine), PAEI

- b - PLPhe

4,8

, in a 0.05 M phosphate buffer at pH

7. Aggregates were observed despite the very low number of hydrophobic l - phe-

nylalanine units, and the size of which was in the order of R

= 425 nm (DLS).

The seemingly high tendency of these polymers to form aggregates was attributed

to the establishment of hydrogen bridges between the amino acid units, as shown

by IR spectroscopy, in addition to hydrophobic interactions. Visualization of the

aggregates with TEM strongly suggested the presence of coacervates or large clus-

ters of small micelles but no vesicles.

The existence of vesicles could be demonstrated for PS

258

- b - PZLLys

in dilute

CCl

solution (Losik and Schlaad [47] ). Scanning electron microscopy (SEM)

showed collapsed hollow spheres of about 300 – 600 nm in diameter, indicative of

vesicles, and also sheet - like structures, supposedly bi - layers that are not yet closed

to vesicles (Figure 27.2 A) [15] . The preference for a lamellar structure might be,

as in the previous examples, attributed to a stiffening of the core by the 2D - arrange-

ment of crystallizable PZLLys α - helices. PS

258

- b - PZLLys

109

, on the other hand, was

found to form large compact ﬁ brils being hundreds of nanometers in diameter

and several tens of microns in length (Figure 27.2 B); these aggregates might be

cylindrical multi - lamellar vesicles. However, the processes involved in the forma-

tion of these structures are not yet known.

Likewise, Lecommandoux and coworkers [31] found vesicles for PB

- b - PLGlu

in THF and in CH

solution ( R

= 106 – 108 nm, DLS/SLS). The formation of

Figure 27.2 SEM images of the aggregates formed by

(A) PS

258

- b - PZLLys

and (B) PS

258

- b - PZLLys

109

in dilute CCl

solution; specimens were prepared by shock - freezing a

0.2 wt - % polymer solution with liquid nitrogen and

subsequent freeze - drying [47] .

27.2 Solution Self-assembly of Polypeptide-based Block Copolymers 841

vesicles rather than micelles was attributed to the α - helical rod - like secondary

structure of the insoluble PLGlu that forms a planar interface.

27.2.1.2 Block Copolypeptides

Besides the polypeptide hybrid block copolymers described earlier, a few purely

peptide - based amphiphiles and block/random copolymers (copolypeptides) exist.

In the latter case, both the core and corona of aggregates consist of a polypeptide.

All of the studies reported so far have dealt with aggregation in aqueous media.

Doi and coworkers [48, 49] observed the spontaneous formation of aggregates

of PMLGlu

with a phosphate (P) head group in water. Immediately after sonica-

tion, the freshly prepared solution contained globular assemblies (diameter: 50 –

100 nm, TEM), which after 1 h transformed into ﬁ brous aggregates, promoted by

intermolecular hydrogen bonding between peptide chains. After one day, these

ﬁ brils assembled into a twisted ribbon - like aggregate (TEM). As its thickness

was ≈ 4 nm, which is close to the contour length of PMLGlu

- P in a β - sheet con-

formation (CD and FT - IR spectroscopy), these workers concluded that the forma-

tion of the ribbon was driven by a stacking of anti - parallel β - sheets via hydrophobic

interactions (see above) [22] .

Lecommandoux and coworkers [50] showed that zwitterionic PLGlu

- b - PLLys

in water can self - assemble into unilamellar vesicles with a hydrodynamic radius

of greater than 100 nm (Figure 27.3 ). A change in the pH from 3 to 12 induced

an inversion of the structure of the membrane (NMR) and was accompanied by

an increase in the size of vesicles from 110 to 175 nm (DLS).

Non - ionic block copolypeptides made of l - leucine and ethylene glycol modiﬁ ed

l - lysine residues, PLLeu

10 – 75

- b - PELLys

60 – 200

, were described by Deming and cowork-

ers [51] . The copolymers adopted a rod - like conformation, due to the strong ten-

dency of both segments to form ct - helices, as conﬁ rmed by CD spectroscopy. The

self - assembled structures observed in aqueous solutions included (sub - ) microm-

eter vesicles, sheet - like membranes and irregular aggregates. Here again, it was

shown that the vesicle formation is related to the systematic presence of the

polypeptide in a rod - like conformation in the hydrophobic part of the membrane,

inducing a low interfacial curvature and as a result a hollow structure.

Figure 27.3 Schematic representation of the self - assembly of

zwitterionic PLGlu

- b - PLLys

in water into unilamellar

vesicles [50] .

842 27 Self-assembly of Linear Polypeptide-based Block Copolymers

Meyrueix and coworkers [52] performed the selective precipitation of PLLeu

180

b - PLGlu

l80

and obtained nanoparticles, which could be puriﬁ ed and further sus-

pended in water or in a 0.15 M phosphate saline buffer at pH 7.4. The colloidal

dispersions were stable, due to the electrosteric stabilization of the particles by

poly(sodium l - glutamate) brushes, containing spherical or cylindrical micelles,

besides the large hexagonally - shaped platelets with a diameter of about 200 nm

(TEM). Different shapes of particles were due to the heterogeneity of copolymer

chains with respect to chemical composition (NMR): glutamate - rich chains formed

micelles and leucine - rich ones formed platelets. CD spectroscopy and X - ray dif-

fraction suggested that the core of platelets consisted of crystalline, helical PLLeu

segments, and the structural driving force was thus related to the formation of

leucine zippers in a three - dimensional array.

27.2.2

Polypeptide - based Hydrogels

Protein - based hydrogels are used for many applications, ranging from food and

cosmetic thickeners to support matrices for drug delivery and tissue replacement.

These materials are usually prepared using proteins extracted from natural

resources, which can give rise to inconsistent properties unsuitable for medical

applications.

Recently, Deming and coworkers [53 – 56] designed and synthesized diblock

copolypeptide amphiphiles containing charged and hydrophobic segments. It was

found and demonstrated that gelation depends not only on the amphiphilic nature

of the polypeptides, but also on chain conformation, meaning α - helix, β - strand or

random coil. Speciﬁ c rheological measurements were performed to evidence the

self - assembly process responsible for gelation [55] : the rod - like helical secondary

structure of enantiomerically pure PLLeu blocks is instrumental for gelation at

polypeptide concentrations as low as 0.25 wt - %. The hydrophilic polyelectrolyte

segments have stretched coil conﬁ gurations and stabilize the twisted ﬁ brillar

assemblies by forming a corona around the hydrophobic cores (Figure 27.4 ).

Interestingly, these hydrogels can retain their mechanical strength up to tem-

peratures of about 90 ° C and recover rapidly after stress. This new mode of assem-

bly was found to give rise to polypeptide hydrogels with a unique combination of

properties, such as heat stability and injectability, making them attractive for

applications in foods, personal care products and medicine. In this context, their

potential application as tissue engineering scaffolds has been recently studied [57] .

27.2.3

Organic/Inorganic Hybrid Structures

Recently, polypeptide - based copolymers have also been used for the stabiliza-

tion or synthesis of inorganic species. As a ﬁ rst example, Stucky and coworkers

[58] used block copolypeptides to direct the self - assembly of silica into

spherical and columnar morphologies at room temperature and neutral pH.

27.2 Solution Self-assembly of Polypeptide-based Block Copolymers 843

Stucky, Deming and colleagues [59] also designed a double - hydrophilic block

copolypeptide poly{ N

- 2[2 - (2 - methoxyethoxy)ethoxy]acetyl l - lysine}

100

- b -

poly(sodium l - aspartate)

(PELLys - b - PNaLAsp) that can direct the crystallization

of calcium carbonate into microspheres. They incorporated PLAsp in the diblock

because domains of anionic aspartate residues are known to nucleate calcium

carbonate crystallization. This effect is believed to be caused by matching

interactions between aspartate and the atomic spacing of certain crystal faces

in the growing mineral.

Also worth mentioning is the application of polypeptide - based copolymers in

the production of magnetic nanocomposite materials. Lecommandoux et al. [60]

obtained stable dispersions of super - paramagnetic micelles and vesicles by com-

bining an aqueous solution of PB

- b - PLGlu

56 – 145

with a ferroﬂ uid consisting of

maghemite ( γ - Fe

) nanoparticles. Incorporation of one mass equivalent of

ferroﬂ uid into the hydrophobic core of aggregates did not alter their morphol-

ogy, as deduced from SLS and SANS data, but caused a substantial increase

in the outer diameter by a factor of 6 (DLS). Interestingly, the hybrid vesicles

underwent deformation under a magnetic ﬁ eld, as shown by 2D - SANS experi-

ments. Held and coworkers [61] earlier reported that monodisperse, highly crys-

talline maghemite nanoparticles in organic solvents could be transferred into

an aqueous medium using tetramethylammonium hydroxide stabilized at neutral

pH. Combination of the aqueous maghemite solution with PELLys

100

- b -

PAsp

led to the formation of uniform clusters comprising approximately 20

nanoparticles (Figure 27.5 ).

Figure 27.4 Drawings showing (a)

representation of a block copolypeptide chain

and (b) proposed packing of block

copolypeptide amphiphiles into twisted

ﬁ brillar tapes, with helices packed

perpendicular to the ﬁ bril axes. Polylysine

chains were omitted from the ﬁ bril drawing

for clarity (reprinted from [55] with permission

of The American Chemical Society) .

844 27 Self-assembly of Linear Polypeptide-based Block Copolymers

27.3

Solid - state Structures of Polypeptide - based Block Copolymers

27.3.1

Diblock Copolymers

27.3.1.1 Polydiene - based Diblock Copolymers

One of the ﬁ rst reports on the nanoscale solid - state structure of peptide – synthetic

hybrid block copolymers was published by Gallot and coworkers [62] in 1976. In

this publication, the solid - state structure of a series of PB - b - PBLGlu and PB - b -

PHLGln diblock copolymers was investigated using a combination of techniques,

including infrared and CD spectroscopy, X - ray scattering and TEM. The block

copolymers covered a broad composition range with peptide contents ranging

from 19 to 75%. Interestingly, SAXS revealed a well - ordered lamellar superstruc-

ture characterized by up to four higher - order Bragg spacings for all of the inves-

tigated samples. The lamellar superstructure was conﬁ rmed by electron microscopy

experiments, which were carried out on OsO

- stained specimens. The intersheet

spacings determined from the electron micrographs were in good agreement with

the diffraction data. Wide - angle X - ray scattering (WAXS) experiments indicated

that the α - helical peptide blocks were assembled in a hexagonal array. For a

number of block copolymer samples it was found that the calculated length of

the peptide helix was larger than the thickness of the polypeptide layer. To accom-

modate this difference, it was proposed that the peptide helices were folded in

the peptide layer. The lamellar structure consists of plane, parallel equidistant

sheets. Each sheet is obtained by superposition of two layers: (1) the PB chains

in a more or less random coil conformation and (2) the α - helical polypeptide

blocks in a hexagonal array of folded chains. The hexagonal - in - lamellar structure

was also found for PB - b - PZLLys and PB - b - PLLys block copolymers by the same

Figure 27.5 TEM images of clusters of maghemite

nanoparticles deposited from dispersions in water in the

presence of PELLys

100

- b - PAsp

(reprinted from [61] with

permission of The American Chemical Society) .

27.3 Solid-state Structures of Polypeptide-based Block Copolymers 845

workers [63 – 66] . In the case of the PB - PLLys block copolymers, no periodic

arrangement of the PLLys chains in the peptide layer was found. This is due to

the fact that the polypeptide segments in these block copolymers are not exclu-

sively α - helical but are composed roughly of 50% random coil, 35% α - helix and

15% β - strand domains [63] .

More recently, the solid - state nanoscale structure of PI - b - PZLLys diblock copoly-

mers was reported [34] . Diblock copolymers composed of a P1 block with a

number - average degree of polymerization of 49 and a PZLLys block containing

61 – 178 amino acid residues were investigated with dynamic mechanical analysis

and X - ray scattering. For the PI

- b - PZLLys

, PI

- b - PZLLys

and PI

- b - PZLLys

the X - ray scattering data were in agreement with a hexagonal - in - lamellar morphol-

ogy. Interestingly, for PI

- b - PZLLys

the lamellar spacing was found to decrease

when the samples were prepared from dioxane instead of THF/ N , N - dimethylfor-

mamide (DMF) and suggested folding of the peptide helices. For PI

- b - PZLLys

123

and PI

- b - PZLLys

178

a hexagonal - in - hexagonal structure was found. This morphol-

ogy is illustrated in Figure 27.6 . This structure is unprecedented for polydiene -

based peptide hybrid block copolymers, but has also been found for low molecular

weight PS - b - PBLGlu copolymers [73] .

27.3.1.2 Polystyrene - based Diblock Copolymers

In an early study, Gallot and coworkers [64] reported on the bulk nanoscale struc-

ture of PS - b - PZLLys diblock copolymers, which were based on a PS block with a

number - average molecular weight of M

= 37 kg mol

− 1

and had peptide contents

ranging from 18 to 80 mol - %. X - ray scattering patterns of dry samples that had

been evaporated from dioxane showed two sets of signals, characteristic of a

hexagonal - in - lamellar superstructure. At very low angles, Bragg spacings charac-

teristic of a layered superstructure were found, whereas at somewhat larger angles,

Figure 27.6 Schematic model representation of the hexagonal

in hexagonal (HH) morphology obtained for Pl

- b - PZLLys

178

copolymer cast from dioxane solution.

846 27 Self-assembly of Linear Polypeptide-based Block Copolymers

there was a second set of reﬂ ections pointing towards a hexagonal arrangement

of peptide helices. 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 was also

proposed for the PB - based block copolymer described earlier (Figure 27.7 ).

Removal of the of the side - chain protective groups of the peptide segment

resulted in PS - b - PLLys diblock copolymers [63] . These copolymers were not water

soluble, but formed mesomorphic gels at water contents of less than 50%. The

X - ray scattering patterns indicated a lamellar superstructure, both in the gel state

and the dry samples. In contrast to the side - chain protected block copolymers, no

evidence for a periodic arrangement of the peptide chains was found. This is not

too surprising considering that IR spectra indicated that roughly 50% of the

peptide blocks have a random coil conformation, 35% an α - helical secondary

structure and 15% a β - strand conformation.

Along the same lines, Douy and Gallot [66] also studied the bulk nanoscale

organization of PS - b - PBLGlu. For block copolymers composed of a PS block with

= 25 kg mol

− 1

and containing 31 – 94 mol - % peptide, the same hexagonal - in -

lamellar morphology as described above for the PS - b - PZLLys was found. The

biocompatibility of PS - b - PBLGlu copolymers has been discussed in two publica-

tions [67, 68] . Mori et al. [68] studied diblock copolymers composed of a PS block

with a number - average degree of polymerization of 87 and PBLGlu segments with

number - average degrees of polymerization of 23, 52 or 83. Thrombus formation

was assessed by exposing ﬁ lms of the diblock copolymers and the corresponding

homopolypeptides to fresh canine blood. It was found that thrombus formation

on the diblock copolymer ﬁ lms was reduced compared with the corresponding

homopolymers. For the block copolymers, thrombus formation decreased with

decreasing PBLGlu block length. Also, adsorption of plasma proteins such as

bovine serum albumine, bovine γ - globulin and bovine plasma ﬁ brinogen was

reduced on the block copolymers compared with PS homopolymer.

The characterization of the solid - state nanoscale organization of PS - polypeptide

hybrid block copolymers has recently been reﬁ ned in a series of publications by

Figure 27.7 Schematic model representation of the hexagonal -

in - lamellar (HL) morphology obtained for polypeptide - based

rod – coil diblock copolymers cast from solutions.

27.3 Solid-state Structures of Polypeptide-based Block Copolymers 847

Schlaad and coworkers [69 – 71] . In a ﬁ rst report, three PS - b - PZLLys diblock copoly-

mers with peptide volume fractions of 0.48, 0.74 and 0.82 were investigated [69] .

SAXS patterns recorded from DMF cast ﬁ lms conﬁ rmed the hexagonal - in - lamellar

morphology published earlier by Gallot and coworkers [64] . In their paper, Schlaad

and coworkers went a step further and analyzed their SAXS data using the

interface - distribution concept and the curvature - interface formalism. These evalu-

ation techniques suggested that the bulk nanoscale structure of the PS - b - PZLLys

diblock copolymers does not consist of plain but of undulated lamellae. The

concept of the interface - distribution function and the curvature - interface formal-

ism were also applied to compare the solid - state structures of two virtually identical

PS based diblock copolymers; PS

- b - PZLLys

111

( φ

peptide

= 0.82) and PS

- b - PBLGlu

104

( φ

peptide

= 0.79) [70] . Analysis of the SAXS data obtained on DMF - cast ﬁ lms indi-

cated a hexagonal - in - undulated (or zigzag) lamellar morphology for both block

copolymers. However, the X - ray data also revealed two striking differences

between the samples. The ﬁ rst difference concerns the thickness of the layers,

which are a factor of three smaller for PS

- b - PBLGlu

104

as compared with PS

b - PZLLys

111

. Whereas the PZLLys helices are fully stretched, the PBLGlu helices

are folded twice in the layers. As peptide folding increases the area per chain at

the PS - PBLGlu interface, the thickness of the PS layers also has to decrease in

order to cover the increased interfacial area. The second difference concerns the

packing of the peptide helices. For the PZLLys - based diblock copolymer it was

estimated that about 180 peptide helices form an ordered domain. The level of

ordering, however, was considerably lower for the peptide blocks of PS

- b -

PBLGlu

104

and only ≈ 80 helices were estimated to form a single hexagonally

ordered domain.

In addition, the inﬂ uence of the polydispersity of the polypeptide block on the

solid - state morphology of PS - b - PZLLys diblock copolymers has also been studied

[71] . To this end, a series of ﬁ ve diblock copolymers was prepared from an identical

ω - amino - polystyrene macroinitiator ( P

= 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 conﬁ rmed, as expected,

the hexagonal - in - undulated (or zigzag) lamellar solid - state morphology. Fractiona-

tion of the peptide helices according to their length leads (locally) to the formation

of an almost plane, parallel lamellar interface, which is disrupted by kinks (undula-

tions). The curvature at the PS - PZLLys interface, however, was found to be strongly

dependent on the chain length distribution of the peptide block. Block copolymers

with the smallest molecular weight distribution produced lamellar structures with

the least curvature. Increasing the chain length distribution of the peptide block

(block copolymers with PDI ≈ 1.25) leads to larger ﬂ uctuations in the thickness of

the PZLLys layers, which increases the number of kinks and the curvature at the

lamellar interface. At even larger polydispersities (PDI ≈ 1.64), however, the

number of kinks decreases again. With increasing polydispersity of the peptide

block, the thickness ﬂ uctuations become larger and larger, as does the interfacial

area. At a certain point, at sufﬁ ciently high polydispersity, the system tries to

848 27 Self-assembly of Linear Polypeptide-based Block Copolymers

compensate for the increased interfacial tension and minimizes the number of

kinks (Figure 27.8 ).

Ludwigs et al. [72] used SFM to investigate the formation of hierarchical struc-

tures of PS

- b - PBLGlu

104

in thin ﬁ lms. Thin ﬁ lms 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 THF vapor to achieve a controlled

crystallization of the α - helical PBLGlu. On the smallest length - scale, the structure

was found to be built of short ribbons or lamellae of interdigitated polymer chains.

PBLGlu helices were fully stretched in thin ﬁ lms, 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 27.9 ).

The examples discussed so far have all involved relatively high molecular weight

diblock copolymers. In these cases, the molecular weight of the polypeptide block

is usually sufﬁ ciently 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 signiﬁ cantly decreased. The

inﬂ uence of molecular weight on the solid - state organization of polystyrene - based

peptide – synthetic hybrid block copolymers has been studied for a series of low -

molecular weight PS - b - PBLGlu and PS - b - PZLLys [73, 74] . These diblock copoly-

mers consisted of a short PS block with P

≈ 10, a polypeptide block containing

≈ 10 to 80 amino acid repeat units and were characterized by means of variable

temperature FT - IR spectroscopy and X - ray scattering. These experiments allowed

the construction of “ phase diagrams ” , which are shown in Figure 27.10 . The phase

diagrams reveal a number of interesting features. At temperatures below 200 ° C

and for sufﬁ ciently long polypeptide blocks, a hexagonal arrangement of the

diblock copolymers was found, analogous to the hexagonal - in - lamellar morphol-

ogy of the high - molecular weight analogues. Upon decreasing the length of the

peptide block, however, several novel solid - state structures were discovered. For

very short peptide block lengths (PS

- b - PBLGlu

, PS

- b - PZLLys

, PS

- b - PZL-

Lys

and PS

- b - PZLLys

) a lamellar supramolecular structure was found. This is

Figure 27.8 Schematic representation of the

disordered zigzag lamellar morphology

formed by polypeptide - based diblock

copolymers with low (A), moderate (B) and

high polydispersity (C) with respect to the

length of helices. Polypeptide helices are

represented as cylinders, and polyvinyl sheets

are depicted in black (reprinted from [71] with

permission of The American Chemical

Society) .