Gerard T. Caneba
Precipitation Polymerization
The focus of this effort is the free-radical retrograde-precipitation polymerization (FRRPP) process that he discovered in the late 1980s. Here, polymerization occurs above the lower critical solution temperature (LCST) of the polymerization system. The local heating that occurs in exothermic chain polymerization systems drives the system into the spinodal curve, wherein diffusional mass fluxes have been found to vanish. Monomer molecules, while undergoing Brownian motion, cannot diffuse from high-concentration regions to low-concentration regions adjacent to the reactive sites.
The net result of this and the precipitation into high-polymer concentration is the drastic drop in propagation-rate coefficient relative to termination-rate coefficient, which is opposite to a runaway situation in polymer systems (referred to as the gel effect). We therefore called the mechanism of the FRRPP process an Anti-Gel Effect Phenomenon.
Other results of this mechanism are efficient trapping of polymer radicals, relatively narrow molecular weight distributions, stable molecular weight and poly-dispersity index, and reduced conversion rate. Radical trapping results in up to 84 percent of stable polymer radicals existing relative to all polymeric species even after almost all initiator molecules have already decomposed. This result was the basis for our work in the formation of high yields of block copolymers from a free-radical chemistry.
Reactive Processing of Polymers
We have recently embarked on a program whereby a novel reactive processing method is being used to form interpenetrating polymer networks (IPNs). Instead of polymerizing monomer(s) in the presence of a pre-existing polymer, our newly discovered approach is to reactively blend a polymer mixture in such a way that at least one of the polymeric species is partially degraded and reformed in the same processing equipment. The advantage of this approach is that it does not involve monomeric feed materials, thereby eliminating the need for handling, use, regeneration, and recycling of these normally hazardous fluids.
Selected Publications