Preparation of poly(ethyleneglycol-co-acrylic acid) microspheres with divinylbenzne as crosslinker by distillation-precipitation polymerization

Monodisperse poly( poly( ethyleneglycol) methyl ether acrylate-co-acrylic acid) ( poly( PEGMA-co-AA)) microspheres were prepared by distillation-precipitation polymerization with divinylbenzene ( DVB) as crosslinker with 2,2'-azobisisobutyronitrile ( AIBN) as initiator in neat acetonitrile without stirring. Under various reaction conditions, four distinct morphologies including the sol, microemulsion, microgels and microspheres were formed during the distillation of the solvent from the reaction system. A 2D morphological map was established as a function of crosslinker concentration and the polar monomer AA concentration, in comonomer feed in the transition between the morphology domains. The effect of the covalent crosslinker DVB on the morphology of the polymer network was investigated in detail at AA fraction of 40 vol%. The ratios of acid to ethylene oxide units presenting in the comonomers dramatically affected the polymer-polymer interaction and hence the morphology of the resultant polymer network. The covalent crosslinking by DVB and the hydrogen bonding crosslinking between two acid units as well as between the acid and ethylene oxide unit played key roles in the formation of monodisperse polymer microspheres.