Poly(ethylene oxide) macromonomer-grafted polymer nanoparticles synthesised by emulsifier-free emulsion polymerisation

Ultrafine polymer nanoparticles based on poly(ethylene oxide) (PEO) macromonomer-grafted polystyrene (PS) have been synthesised by emulsifier-free emulsion polymerisation. In addition to the binary copolymerisation between PEO macromonomer and styrene, ternary copolymerisations were also conducted in the presence of a cationic monomer (2-(methacryloyloxy)ethyl) trimethylammonium chloride (MATMAC) as a second comonomer. The size and charge characteristics of fine nanoparticles were characterised using both photon correlation spectroscopy and transmission electron microscopy techniques as well as colloidal titration. It was found that after PEO chains (repeat unit 9 or higher) were incorporated into the PS latex, the particle size was significantly reduced owing to the steric effect contributed from grafted PEO chains. Ternary copolymerisation using MATMAC as comonomer further reduced the particle size, leading to nanoparticles as small as 60 nm. Increasing the MATMAC feed ratio gradually reduced the final size of the nanoparticle, owing to the enhancement in electrostatic stabilisation, whereas increasing the PEO macromonomer feed ratios led to slightly larger particles but significantly inhibited the agglomeration of primary particles. The formation mechanism of the nano- or microparticles with various sizes during polymerisation is discussed in terms of nucleation, agglomeration and adsorption of primary particles.[PUBLICATION ABSTRACT]