This work highlights the relevance of the interactions between polymer and solvent during precipitation polymerization in order to control the morphology and the size of the precipitated material with at any changes in chemical composition Thus, a thermodynamic model based on Flory Hugings model and among solubility parameters has been proposed in order to control the precipitation process This model is based on the study and chat of the interactions (hydrogen-bonding forces, polar lot forces and spersion forces) between growing polymeric chains and solvent molecules The model was con corioborated by mole than 80 different solvent compositions were used for a ternary solvent mixture (toluene, acetonitrile and 2-propanol) and two different monomer molar ratio feeds (45% MAA, 20% HEMA, and 35% EDMA, 20% MAA, 45% HEMA, and 35% EDMA) The morphologies of the resulting polymer mater at were characterized by scanning electron microscopy and transmission electron microscopy and the patric es sizes were deduced by dynamic light scattering The polymeric particles with different sizes prepared in this work were used to introduce on them magnetic properties The results in this work enable the control of the size chemical composition, and the homogeneous encapsulation of Fe3O4 within different hydrophilic polymeric matrixes by polymerization precipitation, allowing the design of magnetic particles free of any stabilizers