Free Radical Polymerization - Reaction Methods Bulk and solution polymerization A typical recipe: 1 mole monomer 0.01 mole initiator 1 L solvent (optional) 0.01 mole chain transfer agent (optional) Purge system with inert gas to remove dissolved molecular oxygen. Heat the mixture for h at 70°C. Isolate product.

Homogeneous Process AdvantagesDisadvantages Bulk Simple, few ingredients, cheap. Make polymer and use it. Autoacceleration will occur. Possible problems with heat transfer during polymerization. Solution Solvent will absorb exotherm of polymerization; Can avoid auto- acceleration; Polymer ends up in solution, maybe use directly. Must purchase and recover solvent. Must separate polymer from solvent at some point. Possibly environmentally unfriendly.

Suspension polymerization 1.Water insoluble monomer. 2.Water insoluble initiator. 3.Suspending agent (optional). 4.Droplets are 100 to 10-3 mm diameter. "Mini reactors.“

Emulsion Polymerization 1.Water insoluble monomer. 2.Water soluble initiator. 3.Surfactant (except in special cases). 4.Droplets are 10-5 to 10-6 mm diameter. 5.Complicated mechanism.

Mechanism of Emulsion Polymerization The surfactant molecules surround small amounts of monomer molecules, creating micelles. There are also large droplets of monomer that are stabilized by small amounts of surfactant. Initiator forms free radicals in the water, where they may find a few monomers to react with. In any case, the radicals diffuse into the micelles, where they find lots of monomer but no other growing chains to cause termination (at least, for a while). The growing chain is then protected from termination until a second radical diffuses into the micelle. This is why the MW can be so high in emulsion polymerization without slowing the rate of conversion.

Two Phase Process AdvantagesDisadvantages SuspensionSimple, few ingredients, cheap. Reaction medium is mostly water, which absorbs the hear of polymerization. Produces beads that have technological uses (xerographic toner, catalyst carriers, ion exchange resins, substrates for combinatorial synthesis, etc.) Autoacceleration will still occur. Isolation of the polymer can be laborious if you didn't want beads. May need to purify polymer from suspending agent. EmulsionMakes very high MW polymer quickly. Reaction medium is mostly water, which absorbs the hear of polymerization. Creates very tiny particles of polymer that have technological uses (paint, coatings, drug delivery, etc.). Isolation of the polymer can be laborious if you didn't want viny particles. May need to purify polymer from surfactant