Silica nanoparticles (Rh = 70 nm) were functionalized with high dispersity (Đ > 2.3) polycaprolactone at various grafting densities, and the brush properties were investigated using dynamic light scattering. Owing to recent advances in controlled polymerization techniques, low dispersity brushes are easily grafted from nanoparticle surfaces, and these systems have been well studied. However, the effect of high dispersity brushes on nanoparticle surfaces is largely unexplored. Here we discuss the brush properties of high dispersity polycaprolactone-grafted silica nanoparticles. Because of the polymerization conditions used, transesterification events are induced during the polymerization to give brushes with increasing dispersity both as brush length increases and as grafting density is increased (e.g., Đ from 1.32 to 2.39 for σ from 0.21 to 0.61 chains/nm2). All grafting densities showed extended chains in the concentrated polymer brush regime, with brush length, lb, scaling with degree of polymerization, lb ∼ Na, where a = 1.39, 1.47, and 1.84 for the high, mid, and low grafting density sets. This study provides the first experimental insight into the effects of increasing chain dispersity on brush properties of nanoparticle systems. Furthermore, this system offers a facile method to tune dispersity of grafted brushes concurrent with the grafting polymerization. We expect this work to be of significant interest to the ongoing study of fundamental properties of polymer brushes as well as these materials finding use in polymer composite applications and provide enhanced mechanical properties compared to their monodisperse analogues.

Hollow amphiphilic crosslinked nanocapsules were synthesized by sequential grafting-from of crosslinked hydrophobic polycaprolactone (PCL) via ring-opening polymerization and grafting-to of hydrophilic poly(ethylene glycol) (PEG) onto 70 nm silica nanoparticles, followed by removal of the silica core. To accomplish the crosslinking of the PCL layer a bis-caprolactone monomer was used. The effects on the brush properties of PCL grafted silica nanoparticles with crosslinker were investigated. Incorporation of only 0.25 mol% crosslinker in the bulk grafting reaction resulted in dramatic effects, such as significantly enhanced brush length and high molecular weight dispersities. Hollow PCL nanocapsules were synthesized by performing the grafting reaction of PCL with 2.5 mol% crosslinker under dilute conditions. Upon removal of the silica core, a significant increase in hydrodynamic radius was observed due to the relief of constrain of surface tethered chain ends and swelling in a good solvent. PEG was then coupled to particles grafted with crosslinked PCL to yield amphiphilic block polymer grafted silica nanoparticles, which displayed excellent dispersibility in water, and resulted in a contraction of the PCL layer, as determined by dynamic light scattering. Core removal of the amphiphilic block polymer grafted silica nanoparticles gave hollow amphiphilic crosslinked nanocapsules which displayed significant swelling in good, non-selective solvent conditions, and a collapsed hydrophobic core block in aqueous conditions. Finally, the amphiphilic materials, both before and after core removal, were determined to be effective at stabilizing hydrocarbons in water, with the hollow nanocapsules having ca. 15 times greater uptake capacity.

A series of novel organogels were synthesized from poly(propylene oxide) (PPO) functionalized with main chain urea moieties which provided rapid gelation and high moduli in a variety of solvents. Three different molecular weight PPOs were used in this study: 430, 2000, and 4000 g mol−1, each with α,ω-amino-end groups. Four urea groups were introduced into the main chain by reaction with hexamethylene diisocyanate followed by subsequent reaction with a monofunctional alkyl or aromatic amine. This PPO/urea gelator was found to form gels in carbon tetrachloride, chloroform, dichloromethane, toluene, ethyl acetate, and tetrahydrofuran. Among these, carbon tetrachloride and toluene were found to be the best solvents for this system, resulting in perfectly clear gels with high moduli at low mass fraction for PPO-2000 systems. Flory–Huggins polymer–solvent interaction parameter, χ, was found to be a useful indicator of gel quality for these systems, with χCCl4/PPO-2000 < 0.5 and χtoluene/PPO-2000 ≈ 0.5. Systems with χ parameters >0.5 were found to form low moduli gels, indicating that for these systems, polymer–solvent interaction parameters can be a useful predictor of gel quality in different solvent systems.