Magnetic Resonance Imaging of Spiral Patterns in Crosslinked Polymer Gels Produced via Frontal Polymerization

摘要

Frontal polymerization is a process in which a lOcalized reaction zone propagates through a monomer reactant mixture, leaVing a polymer product in its..' wake, and is the result of the coupling of the thermal transport and Arrhenius depen- dence of the exothermic polymerization. Under most conditions, a planar front is stable. However, for multifunctional acrylates at room temperature, fronts may propagate iri' a helical fashion along the axis of the reactor. This front propagation is typical of what., is called a spin mode, in which the subsequent polymer sample has alternating spiral' patterns of low and high monomer conversion eVident on the sample surface. For the first time, we demonstrate that magnetic resonance imaging on a submillimeter scale, can be used to show that the spiral patterns are not restricted to the sample surface but are distributed throughout the volume. Samples were soaked in water, and the trans- verse proton relaxation times were imaged. The results suggest proton mobility is smaller in the high-conversion region in which the hot spot propagated than in the low-conversion region.