Provided the plastic doesn't need significantly more space than the source material, of course. We all know what happens when you try freezing a sealed bottle filled with water.
Than what? Genuinely curious. I thought that the main exothermic thing monomers did was polymerization or combustion, and we're really hoping to prevent the latter.
If so, that could be one of the best outcomes. As long as it does not blow up before the process completes.