AUTO-ACCELERATION OF FREE-RADICAL POLYMERIZATION .4. PREDISSOLVED POLYMER

The onset of autoacceleration of free-radical polymerization occurs when a critical concentration of polymer is formed from the monomer. This concentration can be predicted approximately from a theory which attributes the critical concentration to a condition of macromolecular close packing. The objective of the present work was to find whether quantitatively equivalent effects could be realized in the case where polymer was predissolved in monomer. Approximately, this was found when poly(methyl methacrylate) (PMMA) was predissolved in methyl methacrylate and then polymerization initiated by benzoyl peroxide. Similar experiments but with polystyrene in place of PMMA gave erratic results because of phase separation. Polystyrene predissolved in styrene was less effective in bringing on autoacceleration than in the case where polystyrene is formed in situ from monomer. It is tentatively suggested that this is because made-up solutions of polystyrene offer less resistance to the diffusion of polymer free radicals. © 1979, American Chemical Society. All rights reserved.