Synthesis of hemispherical poly(2-hydroxylethyl methacrylate-co-methyl methacrylate)/poly(styrene-co-glycidyl methacrylate) composite particles with heterobifunctional groups by soap-free seeded emulsion polymerization

Poly(2-hydroxylethyl methacrylate-co-methyl methacrylate)/poly(styrene-co-glycidyl methacrylate) (P(HEMA-MMA))/P(St-GMA)) composite polymer particles were prepared by soap-free seeded emulsion polymerization. The P(HEMA-MMA) seed latexes cross-linked by 0, 10, and 20 wt % ethylene glycol dimethacrylate (EGDMA) were prepared by soap-free emulsion polymerization with different HEMA/ MMA monomer composition at 80 degreesC. 2,2'-Azobis(2-amidinopropane) dihydrochloride (V-50) was used as an initiator in the two stages. The morphologies of composite particles were investigated by using seed particles with various HEMA content and cross-link degree, and the effects of solvent addition, preswelling of seed particles by monomers and solvent, and the weight ratio of secondary monomer to seed particles (M/P) on the particle morphology were discussed. Un-cross-linked P(HEMA-MMA) seed latex showed the property of gel particles capable of being swollen by water, which led to the instability of seed particles and a specific morphology variation. In principle, the addition of solvent favors to form thermodynamically stable morphology, but the preswelling process by monomers and toluene did not affect the particle morphology, possibly because the equilibrium swelling might be already attained during the nitrogen purge and heating intervals under lower M/P ratio. Various spherical and anomalous particle morphologies were obtained by controlling polymerization conditions; that is, sandwich-like, hemispherical, and microphase-separated spherical particles were formed when the seed particles with lower HEMA content and lower cross-link degree were employed under smaller M/P ratio. On the other hand, dumbbell, popcorn, and bunch of grapes like anomalous particles were formed under some specific conditions. When the cross-linker, divinylbenzene (DVB), was charged into the seed stage, the anomalous particles were changed to spherical particles due to the reduction of polymer chain mobility.