Synthesis of core–shell microspheres with active hydroxyl groups by two‐stage precipitation polymerization

Monodisperse micrometer microspheres having active hydroxyl groups with a dense core and a lightly crosslinked functional shell were prepared by two‐stage precipitation polymerization in the absence of any stabilizer. Commercial divinylbenzene (DVB), containing 80 % of DVB was polymerized by precipitation in acetonitrile without any stabilizer as the first stage polymerization and used as the core. When the conversion of DVB was about 60 % in the first stage, hydroxyethyl methacrylate (HEMA) and azobisisobutyronitrile (AIBN) were introduced into the reaction system and copolymerized with unreacted DVB on the core surface to form a lightly crosslinked functional shell with hydroxyl groups formed on the surface during the second stage precipitation polymerization. Both the crosslinking degree and the thickness of the shell layer depend on HEMA loading. The kinetic study demonstrated that the conversion of HEMA increased slightly with increasing HEMA loading. Higher HEMA loading and AIBN concentration increased the reaction rate significantly and formed more soluble oligomers, which resulted in secondary initiation with high HEMA loading. The resulting core–shell polymer particles were characterized with scanning electron microscopy (SEM), and FTIR.