Synthesis of polybutadiene-silica nanoparticles via differential microemulsion polymerization and their hydrogenated nanoparticles by diimide reduction

Internal Microstructure Dictates Interactions of Polymer-grafted Nanoparticles in Solution

Understanding the effects of polymer brush architecture on particle interactions in solution is requisite to enable the development of functional materials based on self-assembled polymer-grafted nanoparticles (GNPs). Static and dynamic light scattering of polystyrene-grafted silica particle solutions in toluene reveals that the pair interaction potential, inferred from the second virial coefficient, A 2, is strongly affected by the grafting density, σ, and degree of polymerization, N, of tethered chains. In the limit of intermediate σ (∼0.3 to 0.6 nm-2) and high N, A 2 is positive and increases with N. This confirms the good solvent conditions and can be qualitatively rationalized on the basis of a pair interaction potential derived for grafted (brush) particles. In contrast, for high σ > 0.6 nm-2 and low N, A 2 displays an unexpected reversal to negative values, thus indicating poor solvent conditions. These findings are rationalized by means of a simple analysis based on a coarse-grained brush potential, which balances the attractive core-core interactions and the excluded volume interactions imparted by the polymer grafts. The results suggest that the steric crowding of polymer ligands in dense GNP systems may fundamentally alter the interactions between brush particles in solution and highlight the crucial role of architecture (internal microstructure) on the behavior of hybrid materials. The effect of grafting density also illustrates the opportunity to tailor the physical properties of hybrid materials by altering geometry (or architecture) rather than a variation of the chemical composition.

Polyisoprene-Silica Nanoparticles Synthesized via RAFT Emulsifier-Free Emulsion Polymerization Using Water-Soluble Initiators

Polyisoprene-silica (PIP-co-RAFT-SiO₂) nanoparticles were prepared via reversible addition⁻fragmentation chain-transfer (RAFT) emulsifier-free emulsion polymerization using water-soluble initiators, 4,4'-Azobis (4-cyanopentanoic acid) (ACP) and 2,2'-Azobis (2-methylpropionamidine) dihydrochloride (V50). The particle size of emulsion prepared using ACP initiator was smaller than that using V50 initiator because the V50 initiator was more active toward decomposition than the ACP initiator. A high monomer conversion (84%), grafting efficiency (83%) and small particle size (38 nm) with narrow size distribution were achieved at optimum condition. The PIP-co-RAFT-SiO₂ nanoparticles exhibited core⁻shell morphology with silica encapsulated with polyisoprene (PIP). The new PIP-SiO₂ nanoparticles could be applied as effective filler in rubber composites that possess good mechanical and thermal properties.