Self-Assembly of Mixtures of Telechelic and Monofunctional Amphiphilic Polymers in Water: From Clusters to Flowerlike Micelles

Genetically Fused Resilin-like Polypeptide-Coiled Coil Bundlemer Conjugates Exhibit Tunable Multistimuli-Responsiveness and Undergo Nanofibrillar Assembly

Peptide-based materials are diverse candidates for self-assembly into modularly designed and stimuli-responsive nanostructures with precisely tunable compositions. Here, we genetically fused computationally designed coiled coil-forming peptides to the N- and C-termini of compositionally distinct multistimuli-responsive resilin-like polypeptides (RLPs) of various lengths. The successful expression of these hybrid polypeptides in bacterial hosts was confirmed through techniques such as gel electrophoresis, mass spectrometry, and amino acid analysis. Circular dichroism spectroscopy and ultraviolet-visible turbidimetry demonstrated that despite the fusion of disparate structural and responsive units, the coiled coils remained stable in the hybrid polypeptides, and the sequence-encoded differences in thermoresponsive phase separation of the RLPs were preserved. Cryogenic transmission electron microscopy and coarse-grained modeling showed that after thermal annealing in solution, the hybrid polypeptides adopted a closed loop conformation and assembled into nanofibrils capable of further hierarchically organizing into cluster structures and ribbon-like structures mediated by the self-association tendency of the RLPs.

Effect of chain architecture on the structure, dynamics, and rheology of thermoresponsive poloxamer hydrogels and associated blends

Poloxamers, ABA triblock polymers composed of a poly(propylene oxide) (PPO) midblock (B) and poly(ethylene oxide) (PEO) endblocks (A), are widely studied for biomedical applications. Aqueous poloxamer 407 (P407; also referred to as F127) undergoes a solution-to-gel transition with increasing temperature, driven by the formation and ordering of micelles onto periodic lattices; however, the gel temperature and resulting modulus has limited tunability. Here, reverse P407 (RP407), a BAB polymer of the same composition and molar mass but the inverted architecture, is synthesized via anionic polymerization. The micellization and gelation temperatures of RP407 are higher than that of P407 and the PPO endblocks allow for intermicelle bridging; however, both single-component solutions favor body-centered cubic (BCC) packings. Further, aqueous RP407 displays a "soft gel" region with interesting rheological behavior, including viscoelastic aging and thermal hysteresis. Combining P407 and RP407 yields solutions with intermediate transition temperatures and alters the size and micelle packing. While the single-component solutions produce BCC packings, the blends form close-packed structures and larger micelles of higher aggregation numbers. Blends of P407 with an analogous AB diblock (E111P32) display similar behavior, whereas RP407/diblock blends form intermediate-sized BCC-packed micelles. These differences in packing and aggregation alter the local environments within the gels, which could have implications for applications such as drug delivery and protein stabilization.

Detection and evaluation of polymer–polymer interactions in dilute solutions of associating polymers

An experimental tool for the evaluation of intramolecular associative/hydrophobic interactions in polymer/solvent systems was proposed and tested.

Spherical Micelles with Nonspherical Cores: Effect of Chain Packing on the Micellar Shape

Self-assembly of amphiphilic polymers into micelles is an archetypical example of a "self-confined" system due to the formation of micellar cores with dimensions of a few nanometers. In this work, we investigate the chain packing and resulting shape of C n -PEOx micelles with semicrystalline cores using small/wide-angle X-ray scattering (SAXS/WAXS), contrast-variation small-angle neutron scattering (SANS), and nuclear magnetic resonance spectroscopy (NMR). Interestingly, the n-alkyl chains adopt a rotator-like conformation and pack into prolate ellipses (axial ratio ϵ ≈ 0.5) in the "crystalline" region and abruptly arrange into a more spheroidal shape (ϵ ≈ 0.7) above the melting point. We attribute the distorted spherical shape above the melting point to thermal fluctuations and intrinsic rigidity of the n-alkyl blocks. We also find evidence for a thin dehydrated PEO layer (≤1 nm) close to the micellar core. The results provide substantial insight into the interplay between crystallinity and molecular packing in confinement and the resulting overall micellar shape.

Tale of Two Tails: Molecular Exchange Kinetics of Telechelic Polymer Micelles

Telechelic polymers contain two chain ends that are able to promote self-assembly into "flowerlike" or interconnected micellar structures. Here, we investigate the molecular exchange kinetics of such micelles using time-resolved small-angle neutron scattering. We show that the activation energies of monofunctional and telechelic chain exchange are identical. This demonstrates that the two chain ends are not simultaneously released in a single event. Instead, the results show that, contrary to regular micelles, the kinetics occurs in a multistep process involving a collision-induced single-molecule exchange mechanism where the exchange rate is directly proportional to the polymer concentration. We show that this novel mechanism can be quantitatively explained by a simple kinetic model.

“One-pot” aminolysis/thia-Michael addition preparation of well-defined amphiphilic PVDF-b-PEG-b-PVDF triblock copolymers: self-assembly behaviour in mixed solvents

Novel amphiphilic PVDF-based triblock copolymer (PVDF₅₀-b-PEG₁₃₆-b-PVDF₅₀) is synthesized using RAFT polymerization and a one-pot thia-Michael addition. Self-assembly of this ABA copolymer resulted in formation of original crystalline structures.

Low length dispersity fiber-like micelles from an A–B–A triblock copolymer with terminal crystallizable poly(ferrocenyldimethylsilane) segments via living crystallization-driven self-assembly

Uniform cylindrical micelles with coronas in a looped configuration have been prepared.

Telechelic amphiphilic metallopolymers end-functionalized with platinum(ii) complexes: synthesis, luminescence enhancement, and their self-assembly into flowerlike vesicles and giant flowerlike vesicles

Telechelic amphiphilic metallopolymers can self-assemble in solution to create nanosized flowerlike vesicles, where the two platinum(ii) complex ends are connected to the same vesicular core and the central PEG chains form loops as a corona.

Effect of PCL end-groups on the self-assembly process of Pluronic in aqueous media

Understanding self-assembly of amphiphilic copolymers in aqueous solution is an important issue in many areas, e.g., in order to tailor-make carriers for drugs and genes. We have synthesized modified versions of the copolymer of type PEO-PPO-PEO (Pluronic, F127), with short (PCL(5)) or long (PCL(11)) PCL blocks at both ends. Turbidity, dynamic light scattering (DLS), small angle neutron scattering (SANS), and rheology measurements were carried out on dilute aqueous solutions of these polymers to investigate their self-assembly behavior. The DLS results clearly show that both micellization and inter-micellization can be controlled by polymer concentration, temperature, and length of the PCL block. The interplay between unimers, micelles, and clusters of micelles could be monitored and the size and size distribution of the species were determined. The SANS data could be portrayed by a spherical core-shell model at all considered conditions of temperature and concentration for F127 and PCL(5) apart from F127 at the lowest temperature measured. The SANS data for PCL(11) were described by a spherical core-shell model at low temperatures, whereas at elevated temperatures asymmetric sub-structures appeared and a cylindrical core-shell model was employed in the analysis of the data. The appearance of pronounced correlation peaks at elevated temperatures signalizes marked intermicellar interactions. The shear viscosity data revealed a minor shear thinning effect, suggesting that the interchain structures are rather stable and not easily disrupted. The work shows that PCL-modification of Pluronic has a large influence on the self-assembly process and on the final structure of the assemblies.

Polymerization of long chain alkyl glycidyl ethers: a platform for micellar gels with tailor-made melting points

Controlled polymerization of long-chain alkyl glycidyl ethers (AlkGE) under anionic ring opening conditions is enabled by the addition of 18-crown-6. Capitalizing on this strategy, highly amphiphilic block copolymers are prepared that form hydrogels with adjustable melting points.