KINETICS OF STYRENE UPTAKE BY A POLYURETHANE NETWORK DURING THE FORMATION OF INTERPENETRATING POLYMER NETWORKS

Due to insolubility of the components, formation of interpenetrating p olymer networks (IPNs) requires particular ways of synthesis. Among ot hers, IPNs can be prepared by the sequential technique where a network is swollen in a monomer and its crosslinker, which are then polymeriz ed in situ. The simplest case is to swell at equilibrium; however this leads to IPNs of a given composition. For obtaining other composition s, swelling has to be stopped before equilibrium, or the swollen netwo rk (gel) has to be deswollen to a certain extent. Therefore, diffusivi ty of the monomer within the gel has to be known. The kinetics of mono mer uptake was studied for a polyether urethane/styrene-divinylbenzene system which gives transparent materials despite the difference in re fractive indexes. This allows direct visual observations of the monome r progress within the network. The results are not fully in agreement with the theories of Tanaka and of Candau which both predict the progr ession of a solvent in a polymeric gel. Two regimes of swelling depend ing on the concentration distribution of the monomer within the gel we re found.