In the past, we have been able to show that chain polymerization rate can be controlled if it is accompanied by phase separation above the lower critical solution temperature (LCST) [Caneba, 1992]. We have just embarked on a program whereby reaction control is being used for dimensional control of polymerized species.
In this presentation, we will show the formation of polymer spheres and rods with dry dimensions as small as 50 nm in a surfactant-free fluid. This is based on our work in a well-mixed reactor fluid vessel, where polymer-rich domains tend to agglomerate into larger structures. We think that primary polymer-rich materials start with single-molecule sizes, but uncontrolled polymerization and domain interactions in dilute solution result in agglomerated species. We have been able to freeze some of these small domains by incorporating small amounts of crosslinker in the polymerization mixture. Our system is based on polystyrene with ethylene glycol dimethacrylate as crosslinker. When the crosslinker was added at a later time, we discovered the existence of wet 350-micron polymer-rich spherical particles. This signifies the tendency of the system to agglomerate even in a well-mixed fluid.
In this presentation, we will also show results of controlled polymerization in a quiescent fluid.
Caneba, G.T., "Free-Radical Retrograde-Precipitation Polymerization Process", Advances in Polymer Technology, Vol. 11, p. 277 (1992).
Gerard T. Caneba
Associate Professor, Department of Chemical Engineering, Michigan Technological University
1400 Townsend Drive
Houghton, Michigan 49931 USA