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.