With ethanol and water mixture (H2O-EtOH) as the solvent

precipitation polymerization of trihydroxymethyl propane triacrylate (TMPTA

the crosslinker monomer) and styrene (St) was carried out using 2

2'-azobis-(isobutyronitrile) (AIBN) as the initiator.Microspheres of uniform size were obtained in most of the polymerizations done with varied TMPTA/St mass ratio and in H2O-EtOH with different water amounts.The yields of the microspheres and soluble oligomers were determined.Results indicate that both the yields increased with increased TMPTA in the monomer mixture; whereas with increased water amount in the polymerization solvent

the yield of the microspheres was promoted while that of the soluble oligomers was reduced.Number average size and size distribution of the microspheres were obtained from SEM.Hansen three dimensional solubility parameters (s

h and p) were calculated for the monomers and H2O-EtOH binary solvent

and so were the differences between their solubility parameters.Boundary limitations for the formation of the uniform microspheres were established based on the difference (p) of polar solubility parameters (p) between the solvent and the monomer mixture

and that (h) of hydrogen bonding solubility parameters (h).With three sets of p and h at (5.0

12.4)

(9.2

20.1) and (6.0

10.0) (expressed as p

h)

an enclosed experimental zone was set

uniform microspheres can be expected when the polymerization is conducted within the limits of this enclosed zone.