We demonstrate for the first time spherically propagating frontal polymerization that also exhibits spin modes. We have developed an interesting system using the amine-catalyzed Michael addition of a trithiol to a triacrylate to create a rubbery gel. The gel suppresses convection and bubble formation during front propagation. A peroxide is also present to act as a thermal initiator. The front propagates via free-radical polymerization of the remaining triacrylate after being initiated photochemically in the center of the reactor. It is possible to prepare the rubbery gel in any shape and then initiate thermal frontal polymerization. So-called spin modes have been observed for the first time in spherically propagating fronts in which waves of polymerization propagate on the expanding spherical front. A system using a diacrylate dissolved in dimethyl sulfoxide with added silica gel and with persulfate as the initiator supports spherical fronts but does not exhibit spin modes.
Tschuikow-Roux, E.; Rauk, A. J. Phys. Chem. 1991, 95,9832. (b) Chen, Y.; Rauk, A.; Tschuikow-Roux, E. J. Phys. Chem. 1991, 95.9900. (1 5) Pople, J. A.; Head-Gordon, M.; Fox, D. J.; Raghavachari, K.; Curtis, (16) Corbett, P.; Tarr, A. M.; Whittle, E.A manganese-catalyzed Belousov-Zhabotinskii (BZ) reaction with a mixed hypophosphite/acetone substrate was found to be remarkably sensitive to stirring in a batch reactor. The reaction d a t e d in a container with a gas/liquid interface (either air or nitrogen). However, when the reaction was stirred in a sealed flask with no interface, the system remained in the reduced state. When the slow stirring (about 100 rpm) was stopped, a pink color from Mn(II1) was observed to ascend from the Teflon-coated stir bar. When a glass stir bar was used, the system would oxidize much more slowly than with the Teflon one. A possible mechanism is considered in which bromine loss to the gas phase is crucial for oscillation. In the sealed system, oxidation occurs when the stirring is stopped because bromine can adsorb to the surface of the Teflon, allowing local oxidation which spreads throughout the system.
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