With no any surfactant and in the presence of casein (CA)

nano-sized core/shell latex particles based on methyl methacrylate (MMA)/CA with about 150 nm in diameter

determined by light scattering

were prepared through emulsion polymerization of MMA using tert-butyl hydroperoxide(TBHP) as initiator.The designed coreshell structure was confirmed by TEM observation.Results revealed that a sharp decrease in particle size was observed within the first 20 min of the polymerization

and the particle size remained quite constant afterwards.Monomer conversion reached about 70% within 30 min of the initiation

followed by a very slow increase to about 73% up to 3 h of polymerization.Optimization of the polymerization process demonstrated that

to achieve high MMA conversion

high PMMA grafting on CA and relatively narrow size distribution for the core-shell particles

polymerization temperature should be kept between 70℃ and 80℃

TBHP level at 0.18% to 0.36% of CA mass

MMA/CA ratios at 4/1 by mass and total content of MMA and CA not higher than 10% by weight in the system.Under these conditions

core-shell particles of PMMA-CA with MMA conversion 75% and PMMA grafting on CA 75% were achieved.The results were interpreted based on the mechanism of the initiation and particle formation.