J. Phys. Chem. B 1998, 102, 3927-3929
3927
Frontal Dispersion Polymerization John A. Pojman,* Grady Gunn, Chilibra Patterson, Jim Owens, and Chris Simmons Department of Chemistry and Biochemistry, The UniVersity of Southern Mississippi, Hattiesburg, Mississippi 39406-5043 ReceiVed: March 13, 1998
Frontal polymerization is a promising approach for preparing polymeric materials in which a localized reaction zone propagates through an unstirred medium. Large thermal and compositional gradients occur in the front that can lead to convective instabilities that interfere with the front propagation. With monomers that produce thermoplastic polymers, the Rayleigh-Taylor instability can destroy a descending front as the more dense molten polymer “fingers” into the unreacted monomer. Ascending fronts are not possible because simple convection caused by the heat release of the reaction quenches the front. Using a saltwater dispersion, we have shown for the first time that stable descending fronts with monomers such as benzyl acrylate can propagate through a saltwater dispersion if the density of the aqueous phase is greater than the density of the polymer. However, hydrolysis followed by intermolecular anhydride formation occurs at the high front temperature, resulting in a lightly cross-linked copolymer.
Frontal polymerization is a mode of converting monomer into polymer via a localized reaction zone that propagates, most often through the coupling of thermal diffusion and Arrhenius reaction kinetics. If the product is a thermoplastic, such as poly(benzyl acrylate), the molten polymer produced in a descending front is not hydrodynamically stable but collapses through the Rayleigh-Taylor instability.1,2 In this work we describe a method using monomer/saltwater dispersions that allows for the first time stable descending fronts with monomers that produce thermoplastics. Frontal polymerization reactions were first discovered by Chechilo et al. in 1972.3 Pojman et al. considered the macrokinetics and dynamics of frontal polymerization4 and considered applications for materials synthesis.5 The standard experiment is to initiate a front by heating the top of a solution of a high boiling point monomer containing a few percent of a peroxide or nitrite in a tube. A front propagates at about a cm/ min. Frontal polymerization can be observed (descending fronts) under moderate pressures (
