Polymers with sequence control offer the possibility of tuning segregation strength with comonomer sequence instead of chemical identity. Here, we have synthesized polystyrene-b-polypeptoid diblock copolymers that differ only in the sequence of comonomers in the polypeptoid block, where nonpolar phenyl side chains are incorporated to tune compatibility with polystyrene. Using small-angle X-ray scattering, we see that these materials readily self-assemble into lamellae, with domain spacings and order–disorder transition temperatures varying with sequence, despite identical composition. The ordered state is likely governed by chain conformational effects that localize compatibilizing comonomers at the block–block interface. These altered chain conformations are supported by simulations with self-consistent field theory (SCFT) and lead to the observed changes in domain spacing. However, the trends seen in the order–disorder transition are not captured by SCFT simulations or effective χ parameters, measured in the disordered phase by approximating the copolypeptoid as a uniform block. The disagreement between measured thermodynamic properties and coarse-grained approaches like SCFT and effective χ points to the importance of molecular-scale effects in sequence-defined materials. Additionally, a reversal in relative disordering temperatures between forward and inverse taper sequences is observed compared to previous studies, likely due to a combination of sequence definition at the monomer length scale and the use of a “styrene-like” compatibilizing side chain rather than a true polystyrene repeat unit. These results demonstrate that comonomer sequence tunes chain conformation and segregation strength, suggesting that sequence design could be used to target desired properties and morphologies in block copolymer materials while retaining important chemical functionalities.

Controlling the self-assembly of block copolymers with variable chain shape and stiffness is important for driving the self-assembly of functional materials containing nonideal chains as well as for developing materials with new mesostructures and unique thermodynamic interactions. The polymer helix is a particularly important functional motif. In the helical chain, the traditional scaling relationships between local chain stiffness and space-filling properties are not applicable; this in turn impacts the scaling relationships critical for governing self-assembly. Polypeptoids, a class of sequence-defined peptidomimetic polymers with controlled helical secondary structure, were used to systematically investigate the impact of helical chain shape on block copolymer self-assembly in a series of poly(n-butyl acrylate)-b-polypeptoid block copolymers. Small-angle X-ray scattering (SAXS) of the bulk materials shows that block copolymers form hexagonally packed cylinder domains. By leveraging sequence control, the polypeptoid block was controlled to form a helix only at the part either adjacent to or distant from the block junction. Differences in domain size from SAXS reveal that chain stretching of the helix near the block junction is disfavored, while helical segments at the center of cylindrical domains contribute to unfavorable packing interactions, increasing domain size. Finally, temperature-dependent SAXS shows that helix-containing diblock copolymers disorder at lower temperatures than the equivalent unstructured diblock copolymers; we attribute this to the smaller effective N of the helical structure resulting in a larger entropic gain upon disordering. These results emphasize how current descriptions of rod/coil interactions and conformational asymmetry for coil polymers do not adequately address the behavior of chain secondary structures, where the scalings of space-filling and stiff−elastic properties relative to chain stiffness deviate from those of typical coil, semiflexible, and rodlike polymers.

Understanding the effects of nonideal polymer chain shapes on block copolymer self-assembly is important for designing functional materials, such as biopolymers or conjugated polymers, with controlled selfassembly behavior. While helical chain shapes in block copolymers have been shown to produce unique morphologies, the details of how chain helicity influences the thermodynamics of self-assembly are still unclear.Here, we utilize model coil−coil and coil−helix block copolymers based on polypeptoids, for which the chain shape can be tuned from helix to coil via monomer chirality with otherwise constant chemistry. This model block copolymer system is used to probe the effects of chain helicity on the thermodynamics of block copolymer self-assembly. Smallangle X-ray scattering of the bulk materials shows that the block copolymers form well-ordered lamellar structures. While having identical domain spacing, the coil−helix block copolymer displays a lower order−disorder transition temperature (T ODT ) than its coil−coil analogue. The coil−helix block copolymer is found to have a smaller enthalpic contribution to mixing, supported by a smaller effective Flory−Huggins interaction parameter (χ eff ) determined in the disordered state. Furthermore, the helical block of the coil−helix block copolymer experiences larger chain stretching penalties in the lamellar morphology, which leads to a larger entropic gain upon disordering. The combined effects of the enthalpic and entropic contributions are likely to have lowered the T ODT of the coil−helix block copolymer, yielding insight into the importance of different thermodynamic contributions that arise from polymer chains with nonideal shapes in block copolymer self-assembly.

The hexagonally close-packed (HCP) sphere phase is predicted to be stable across a narrow region of linear block copolymer phase space, but the small free energy difference separating it from face-centered cubic spheres usually results in phase coexistence. Here, we report the discovery of pure HCP spheres in linear block copolymer melts with A = poly(2,2,2trifluoroethyl acrylate) ("F") and B = poly(2-dodecyl acrylate) ("2D") or poly(4-dodecyl acrylate) ("4D"). In 4DF diblocks and F4DF triblocks, the HCP phase emerges across a substantial range of A-block volume fractions (circa f A = 0.25−0.30), and in F4DF, it forms reversibly when subjected to various processing conditions which suggests an equilibrium state. The time scale associated with forming pure HCP upon quenching from a disordered liquid is intermediate to the ordering kinetics of the Frank−Kasper σ and A15 phases. However, unlike σ and A15, HCP nucleates directly from a supercooled liquid or soft solid without proceeding through an intermediate quasicrystal. Self-consistent field theory calculations indicate the stability of HCP is intimately tied to small amounts of molar mass dispersity (Đ); for example, an HCP-forming F4DF sample with f A = 0.27 has an experimentally measured Đ = 1.04. These insights challenge the conventional wisdom that pure HCP is difficult to access in linear block copolymer melts without the use of blending or other complex processing techniques.

The benefits of incorporating amphiphilic properties into antifouling and fouling-release coatings are well-established. The use of sequence-defined peptides and peptoids in these coatings allows precise control over the spacing and chemistry of the amphiphilic groups, but amphiphilic peptoids have generally outperformed analogous peptides for reasons attributed to differences in backbone structure. The present work demonstrates that the superior properties of peptoids relative to peptides are primarily attributable to a lack of hydrogen bond donors rather than to their secondary structure. A new amphiphilic peptoid was designed containing functional groups similar to those typically found on a hydrogen-bonding peptide backbone. This peptoid and a non-hydrogen-bonding peptoid analogue were incorporated as side chains in PDMS-based polymer scaffolds. Bioassays with the soft algal fouling organisms Ulva linza and Navicula incerta indicate that hydrogen bonding largely determines the differences seen between similar peptide and peptoid species, while sum frequency generation vibrational spectroscopy suggests that the presence of hydrogen bond donors enhances interfacial water structuring. This reduced initial U. linza adhesion, but attached algae were more strongly bound by hydrogen-bonding interactions. Consequently, amphiphilic peptoid materials lacking hydrogen bond donors are better suited to resist marine fouling, with enhanced release of U. linza and similar performance against N. incerta relative to hydrogen-bonding analogues.