Criteria for the preparation of cross-linked poly(meth)acrylate microparticles by solution free radical polymerization

Cross-linked polymer microparticles (CPMs) with nanoscopic size were synthesized from the free radical polymerization of acrylate/diacrylate mixtures or of their methacrylate counterparts. The syntheses were carried out in solution, and the study of the influence of the solvent on the CPM characteristics led to the definition of reliable criteria for the obtention of true, soluble, individualized microgels and for avoiding macro-gelation, when starting from any desired monomer combination. Two main parameters could be pointed out: first, the probability of propagation of the growing radicals, q, (or the kinetic chain length λ = 1/1 − q) that must be kept below a certain threshold value in order to prevent macrogelation; q may be adjusted by playing on the monomer, initiator and transfer agent concentrations. The second essential criterion is the ability of the copolymer for auto-stabilization in the chosen solvent (that may be adjusted by the use of a suitable stabilizing co-monomer in case the quality of the solvent would not be sufficient), in order to avoid flocculation and interparticular reactions. By controlling these two parameters, the preparation of CPMs becomes possible over a wide range of concentration and composition.