Hydrogel microspheres formed by complex coacervation of partially MPEG-grafted poly(styrene-alt-maleic anhydride) with PDADMAC and cross-linking with polyamines

Poly(styrene-alt-maleic anhydride) partially grafted with methoxy poly(ethylene glycol) (SMA-g-MPEG) was prepared by reacting poly(styrene-alt-maleic anhydride) with a substoichiometric amount of MPEG lithium alcoholate. Aqueous solutions of the resulting SMA-g-MPEG formed complex coacervates with poly(diallyldimethylammonium chloride) (PDADMAC). These phase-separated liquid polyelectrolyte complexes were subsequently cross-linked by the addition of two different polyamines to prepare cross-linked hydrogel microspheres. Chitosan served as an effective cross-linker at pH 7.0, while polyethylenimine (PEI) was used as cross-linker under basic conditions (pH 10.5). The resulting coacervate microspheres swelled with increasing salinity, which was attributed mainly due to the shielding of the electrostatic association within the polyelectrolyte complex. The morphology of the coacervate microspheres was investigated by environmental scanning electron microscopy.