Polystyrene Nanoparticles with Anionically Polymerized Polybutadiene Brushes

Abstract

Model hairy nanoparticles of highly cross-linked polystyrene (PS) cores and linear polybutadiene (PBd) brushes were synthesized. The PS cores were obtained using conventional microemulsion polymerization. The linear PBd brushes were synthesized using surface initiated living anionic polymerization. The PS core nanoparticles of 44 ( 12 nm in diameter (volume weight average) were first lithinated using a combination of butyllithium and N,N,N′,N′-tetramethylethylenediamine. Butadiene was subsequently polymerized at the surface of the particles. Two series of samples were synthesized with different degrees of polymerization (N) and grafting densities (σ). In the first series, while σ was constant at ∼0.14 chains/nm 2 (∼500 chains per particle), N changed from 37, 74, 139, to 198. Accordingly, the Mw of brushes changed from 2.0, 4.0, 7.5, to 10.7 kg/mol. In the second series, the weight ratio between PS and PBd was fixed at PS/PBd = 5/2 (σN was constant in this case) and σ varied from 0.15 to 0.08 chains/nm 2 and lower. On the basis of the atomic force microscope (AFM) results, it was found that these hairy particles appeared to obtain better dispersion in PBd matrix as N of grafted chains was increased in the first series. More pronounced changes were observed, such as severe aggregation of particles, when σ decreased from relatively high to low with fixed total weight of brushes in the second series. The results were explained using theoretical calculations for grafted planes in contact with a chemically identical melt. In the system of grafted particles with short brushes (N < P, P is the degree of polymerization of the melt) studied in this paper, it was realized that the parameter σ N can represent the surface characteristics of the particles and be correlated to the dispersion of particles. A higher σ N value corresponds to better dispersion. The properties of cured rubber samples containing hairy particles were also examined using a rubber process analyzer (RPA) and a dynamic mechanical analyzer (DMA). RPA results are consistent with the morphological changes observed with AFM in terms of the "Payne effect". DMA results show that the glass transition temperatures, associated with the core and brushes, shift when the morphology changes. The AFM, RPA, and DMA results prove the strong correlation among the nanostructure of brushes, the microscopic dispersion of particles, and macroscopic properties of nanocomposites.

Polymeric coatings on micro- and nanometric particles for bioapplications

“…The addition of particles considerably increases the surface to volume ratio, and it can thus bring additional impurities, even when great care is taken. Therefore, anionic polymerization initiated from particles remained rather marginal [70,71].…”

Surface treatment and characterization: Perspectives to electrophoresis and lab‐on‐chips

“…Recently, Zheng et al [216] performed the synthesis of polybutadiene brushes from highly crosslinked PS nanoparticles using surface initiated living anionic polymerization. The PS core nanoparticles were first lithiated using a combination of butyllithium and TEMED, and then butadiene polymerized at the surface with a grafting density of 0.14 chains/nm 2 .…”

An investigation on the bound rubber and dynamic mechanical properties of polystyrene particles‐filled elastomer

“…A few reports have involved PS particles as nanofillers to reinforce elastomeric materials. For instance, crosslinked PS nanoparticles with grafted polybutadiene (PB) brushes showed better dispersion in the rubber matrix with increasing brush length . Core–shell polymeric nanoparticles were prepared through self‐assembly and seed‐polymerization technique, showing unique reinforcing performance .…”