Butyl acrylate polymerization Rayleigh-Taylor instability with

Figure 4.11 Rayleigh-Taylor instability with a descending front of butyl acrylate polymerization.

Figure 3. Rayleigh-Taylor instability with descending front of butyl acrylate polymerization. Although the polymer product is hot (> 200 °C) it still is about 20% more dense than the monomer below it.

Frontal polymerization can be achieved with a variety of monomers and has been studied with thermosets and thermoplastics. Examples include n-butyl acrylate, benzyl acrylate, styrene, dodecyl acrylate and hexyl acrylate. If the front is ascending, the monomer inmiediately above the front is lower in density because of the temperature gradient than the bulk monomer and so simple convection can occur for a thermoset (/P) or a thermoplastic. 20) A descending front with a thermoset is stable but a thermoplastic is unstable because even though the polymer is very hot, it is more dense than the unreacted monomer. This leads to the Rayleigh-Taylor instability. 16,21)... 

The most pernicious convective instability occurs with monomers that produce a molten polymer at the front, such as n-butyl acrylate, styrene and methyl methacrylate. A Rayleigh-Taylor instability (2, 25 ), which also appears as fingers as the more dense molten polymer streams down from the reaction zone and destroys the front (Figure 16). The only currently available methods to study frontal polymerization with thermoplastics are to add a crosslinking monomer to produce a thermoset or to increase the viscosity with a viscosifier such as ultrafine silica gel (CAB-O-SBL). To prepare pure poly(n-butyl acrylate) frontally, Pojman et al resorted to performing the reaction under weightless conditions of a sounding rocket (26 ). 

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