POROUS STRUCTURE FORMATION AND SWELLING PROPERTIES OF STYRENE-DIVINYLBENZENE COPOLYMERS

Styrene-divinylbenzene copolymers have been synthesized by suspension polymerization in the presence of toluene (Tol) and heptane (Hep) as diluents for the monomers. The effects of Tol/Hep ratio, dilution of the monomers and divinylbenzene (DVB) content on the porous structure formation and swelling properties of the copolymers were investigated. Each system presented critical concentrations of diluent and DVB for the production of macroporous copolymers. The lower the solvating power of the diluent mixture the lower were the critical concentrations to ensure the formation of fixed pores. Toluene uptakes of macroporous copolymers were considered as a result of three contributions: filling of the fixed pores, expansion of the fixed pores and swelling of the polymeric nuclei. Heptane uptakes can be a result of the two first contributions but heptane cannot swell the nuclei. The expansion of the fixed pores produced an increasing of the volume of the copolymer beads. The kinetic data of heptane uptakes permitted a classification of the porous structures as: gel-type, collapsed, macroporous/collapsed and macroporous. The difference between Tol uptake and Hep uptake was a good measure of swelling of polymer nuclei of copolymers with different porous structures.