Bottlebrush Architecture Research Articles

Solution self-assembly of poly(3-hexylthiophene)–poly(lactide) brush copolymers: impact of side chain arrangement

Solution self-assembly of P3HT-containing copolymers was tailored effectively via bottlebrush architecture, particularly by tuning its side chain arrangement as well as copolymer composition.

Biomimetic Proteoglycans Mimic Macromolecular Architecture and Water Uptake of Natural Proteoglycans.

Aging and degeneration of human tissue come with the loss of tissue water retention and associated changes in physical properties partially due to degradation and subsequent loss of proteoglycans. We demonstrated a novel method of fabrication of biomimetic proteoglycans, which mimic the three-dimensional bottlebrush architecture and physical behavior of natural proteoglycans responsible for tissue hydration and structural integrity. Biomimetic proteoglycans are synthesized by an end-on attachment of natural chondroitin sulfate bristles to a synthetic poly(acryloyl chloride) backbone. Atomic force microscopy imaging suggested three-dimensional core-bristle architecture, and hydrodynamic size of biomimetic proteoglycans was estimated at 61.3 ± 12.3 nm using dynamic light scattering. Water uptake results indicated that biomimetic proteoglycans had a ∼50% increased water uptake compared to native aggrecan and chondroitin sulfate alone. The biomimetic proteoglycans are cytocompatible in the physiological ranges of concentrations and could be potentially used to repair damaged or diseased tissue with depleted proteoglycan content.

Interplay between Molecular Packing, Drug Loading, and Core Cross-Linking in Bottlebrush Copolymer Micelles

Amphiphilic copolymers with bottlebrush architecture provide opportunities for the refinement of materials properties that may not be attainable from their linear analogues. In this study, we investigated the effect of polymer architecture on an interplay between molecular packing inside micelle cores, cargo loading, and core cross-linking. Four families of polylactide-b-poly(ethylene oxide) (PLA–PEO) bottlebrush block copolymers with different side-chain arrangements were synthesized by a combination of grafting-through and grafting-from methods. Copolymers with double-graft PLA side chains produced smaller and more uniform micelles than those with single-graft PLA branches. Photoactive coumarin groups, installed at PLA side chain ends, improved paclitaxel loading efficiencies of the copolymer micelles and allowed for the preparation of uniform, core-cross-linked PLA nanoparticles. The highest paclitaxel uptake (up to 30 wt % of the micelle core) was observed for micelles prepared from bottlebrush copoly...

Complex multiblock bottle-brush architectures by RAFT polymerization.

The combination of the reversible addition fragmentation chain transfer (RAFT) polymerization R-group grafting from approach and RAFT one-pot acrylamide multiblock methodology is used to synthesise complex bottle-brush architectures. This is demonstrated for block copolymer grafted side chains and the insertion of ungrafted blocks into the backbone to yield multi-segmented bottle-brushes.

Soft Poly(dimethylsiloxane) Elastomers from Architecture-Driven Entanglement Free Design.

Soft, solvent-free poly(dimethylsiloxane) elastomers are fabricated by a one-step process via crosslinking bottlebrush polymers. The bottlebrush architecture prevents the formation of entanglements, resulting in elastomers with precisely controllable low moduli from 1 to 100 kPa, below the lower limit of traditional elastomers; moreover, the solvent-free nature enables their negligible adhesiveness compared to commercially available silicone products of similar stiffness.

Nanoparticle stability in biologically relevant media: influence of polymer architecture.

We have contrasted the behavior of nanoparticles formed by the self-assembly of polymers based on poly(ethylene glycol) (PEG) and poly(D,L-lactide), with linear, linear-dendritic and bottle-brush architectures in biologically relevant media. Polymer PEG content ranged between 14% and 46% w/w, and self-assembly was triggered by a rapid and large change in solvent quality inside a four-stream vortex mixer. We examined nanoparticle interaction with human serum albumin (HSA), and solute release in the presence of fetal bovine serum. Dynamic light scattering data showed that PEG surface brushes of all nanoparticles provided effective steric stabilization, thus limiting their interaction with human serum albumin. Calorimetric experiments revealed that nanoparticle-HSA interaction was relatively weak and enthalpically driven, whereas dynamic light scattering results of incubated nanoparticles showed the absence of larger aggregates for most of the polymers examined. Solute core partitioning was examined by the loss of Forster resonance energy transfer (FRET) from a core-loaded donor-acceptor pair. The rate and magnitude of FRET efficiency loss was strongly dependent on the polymer architecture, and was found to be lowest for the bottle-brush, attributed to its covalent nature. Collectively, these findings are expected to impact the molecular design of increasingly stable polymeric carriers for drug delivery applications.

Aqueous self-assembly of giant bottlebrush block copolymer surfactants as shape-tunable building blocks.

Programmed self-assembly of well-defined molecular building blocks enables the fabrication of precisely structured nanomaterials. In this work, we explore a new class of giant polymeric surfactants (Mn = (0.7-4.4) × 10(6) g/mol) with bottlebrush architecture and show that their persistent molecular shape leads to the formation of uniform aggregates in a predictable manner. Amphiphilic bottlebrush block copolymers containing polylactide (PLA) and poly(ethylene oxide) (PEO) side chains were synthesized by a grafting-from method, and their self-assembly in aqueous environment was studied by cryogenic transmission electron microscopy. The produced micelle structures with varying interfacial curvatures and core radii (19-55 nm) boasted rod-like hydrophilic PEO brushes protruding from the hydrophobic PLA cores normal to the interface. Highly uniform spherical micelles with low dispersities were obtained from bottlebrush amphiphiles with packing parameters of ∼0.3, estimated from the polymer structural data. Long cylindrical micelles and other nonspherical aggregates were observed for the first time for compositionally less asymmetric bottlebrush surfactants. Critical micelle concentration values of 1 nM, measured for PEO-rich bottlebrush amphiphiles, indicated an enhanced thermodynamic stability of the produced micelle aggregates. Shape-dependent assembly of bottlebrush surfactants allows for the rational fabrication of a range of micelle structures in narrow morphological windows.

Poly(3-hexylthiophene) Molecular Bottlebrushes via Ring-Opening Metathesis Polymerization: Macromolecular Architecture Enhanced Aggregation.

We report a facile synthetic strategy based on a grafting through approach to prepare well-defined molecular bottlebrushes composed of regioregular poly(3-hexylthiophene) (rr-P3HT) as the conjugated polymeric side chain. To this end, the exo-norbornenyl-functionalized P3HT macromonomer was synthesized by Kumada catalyst transfer polycondensation (KCTP) followed by postpolymerization modifications, and the resulting conjugated macromonomer was successfully polymerized by ring-opening metathesis polymerization (ROMP) in a controlled manner. The P3HT molecular bottlebrushes display an unprecedented strong physical aggregation upon drying during recovery, as verified by several analyses of the solution and solid states. This remarkably strong aggregation behavior is attributed to a significant enhancement in the number of π-π interactions between grafted P3HT side chains, brought about due to the bottlebrush architecture. This behavior is qualitatively supported by coarse-grained molecular dynamics simulations.

Complexes of polyelectrolytes and oppositely charged ionic surfactants

Complex formation between a single polyelectrolyte chain and ionic surfactant molecules is studied by computer simulation of a “primitive” electrolyte model with explicit charges. The surfactant head carries a charge opposite to that of the polyelectrolyte. The neutral flexible tail is modeled by tethered hard spheres. A molecular bottle-brush architecture of the resulting polyelectrolytesurfactant-complex is observed. The end-to-end distance of the polyelectrolyte is found to behave in a nonmonotonic fashion for increasing Coulomb coupling: it first gets stretched and then the stretching is reduced by self-assembling of surfactant molecules along the polyelectrolyte. The end-to-end distance of the polyelectrolyte in the complex is more pronounced for long surfactant tails. Upon addition of salt to the complex, ionic surfactant molecules condensed onto the polyelectrolyte are replaced by salt microions which leads to a weakening of the complex and to reduced end-to-end distance.