Macromolecular Brushes as Stabilizers of Hydrophobic Solute Nanoparticles

Macromolecular brushes bearing poly­(ethylene glycol) and poly­(d,l-lactide) side chains were used to stabilize hydrophobic solute nanoparticles formed by a rapid change in solvent quality. Unlike linear diblock copolymers with the same hydrophilic and hydrophobic block chemistries, the brush copolymer enabled the formation of ellipsoidal β-carotene nanoparticles, which in cosolvent mixtures developed into rod-like structures, resulting from a combination of Ostwald ripening and particle aggregation. The stabilizing ability of the copolymer was highly dependent on the mobility of the hydrophobic component, influenced by its molecular weight. As shown here, asymmetric amphiphilic macromolecular brushes of this type may be used as hydrophobic drug stabilizers and potentially assist the shape control of nonspherical aggregate morphologies

Nanoparticles from Amphiphilic Heterografted Macromolecular Brushes with Short Backbones

Heterografted macromolecular brushes are highly grafted macromolecules with two different side chains attached to a backbone. When endowed with an amphiphilic character, these can serve as unique stabilizers of biphasic systems and solute carriers and yield interesting self-assembled structures. Herein, we report on the solution structure of amphiphilic double-brush copolymers with short backbonesi.e., comparable to the length of the side-chainsin a selective solvent for one of the grafted blocks. As determined by small-angle neutron scattering measurements, poly­(ethylene glycol)/poly­(d,l-lactide) double brushes adopt a cylindrical structure with highly extended backbones in DMSO. In contrast, brushes undergo intermolecular self-assembly into spherical nanoparticles in water, with aggregation numbers that vary inversely with backbone degree of polymerization. While considerably less susceptible to intermolecular association than linear diblocks of similar hydrophobic and hydrophilic block lengths, the inability of the PEG component to maintain their unimolecular form results in well-defined spherical nanoparticles with very low aggregation numbers (3 < <i>N</i>_agg < 10) which could potentially lead to interesting compartmentalized nanomaterials

Nanoparticles from Amphiphilic Heterografted Macromolecular Brushes with Short Backbones

Heterografted macromolecular brushes are highly grafted macromolecules with two different side chains attached to a backbone. When endowed with an amphiphilic character, these can serve as unique stabilizers of biphasic systems and solute carriers and yield interesting self-assembled structures. Herein, we report on the solution structure of amphiphilic double-brush copolymers with short backbonesi.e., comparable to the length of the side-chainsin a selective solvent for one of the grafted blocks. As determined by small-angle neutron scattering measurements, poly­(ethylene glycol)/poly­(d,l-lactide) double brushes adopt a cylindrical structure with highly extended backbones in DMSO. In contrast, brushes undergo intermolecular self-assembly into spherical nanoparticles in water, with aggregation numbers that vary inversely with backbone degree of polymerization. While considerably less susceptible to intermolecular association than linear diblocks of similar hydrophobic and hydrophilic block lengths, the inability of the PEG component to maintain their unimolecular form results in well-defined spherical nanoparticles with very low aggregation numbers (3 < <i>N</i>_agg < 10) which could potentially lead to interesting compartmentalized nanomaterials

Solute-Triggered Morphological Transitions of an Amphiphilic Heterografted Brush Copolymer as a Single-Molecule Drug Carrier

We describe the use of an amphiphilic macromolecular brush based on poly­(ethylene glycol) (PEG) and poly­(d,l-lactide) (PLA) as a stabilizer of hydrophobic solutes. The brush, which in solution adopted an extended backbone conformation consequent with excluded volume effects of the side chains, retained an elongated character in water following the hydrophobic collapse of PLA and the backbone triggered by a rapid change in solvent quality. However, in the presence of hydrophobic solutes at low concentrations in a homogeneous environment, the brush formed spherical unimolecular nanoparticles achieving high solute encapsulation efficiency. As solute content increased and exceeded what appears to be a limit for intramolecular solubilization, intermolecular assembly took place along with the formation of large aggregates, the properties of which were highly dependent on the solute. This first observation of the solute-triggered unimolecular collapse of an amphiphilic macromolecular brush should find important applications for the design of polymeric drug carriers whose properties can be conveniently modified at the single molecule level

Core–Shell Structure and Aggregation Number of Micelles Composed of Amphiphilic Block Copolymers and Amphiphilic Heterografted Polymer Brushes Determined by Small-Angle X‑ray Scattering

A large group of functional nanomaterials employed in biomedical applications, including targeted drug delivery, relies on amphiphilic polymers to encapsulate therapeutic payloads via self-assembly processes. Knowledge of the micelle structures will provide critical insights into design of polymeric drug delivery systems. Core–shell micelles composed of linear diblock copolymers poly­(ethylene glycol)-<i>b</i>-poly­(caprolactone) (PEG-<i>b</i>-PCL), poly­(ethylene oxide)-<i>b</i>-poly­(lactic acid) (PEG-<i>b</i>-PLA), as well as a heterografted brush consisting of a poly­(glycidyl methacrylate) backbone with PEG and PLA branches (PGMA-<i>g</i>-PEG/PLA) were characterized by dynamic light scattering (DLS) and small-angle X-ray scattering (SAXS) measurements to gain structural information regarding the particle morphology, core–shell size, and aggregation number. The structural information at this quasi-equilibrium state can also be used as a reference when studying the kinetics of polymer micellization