Bulk Polymerisation. Polymerisation in bulk, perhaps the most obvious method of synthesis of polymers, is widely practised in the manufacture of condensation polymers, where the reactions are only mildly exothermic, and most of the reaction occurs when the viscosity of the mixture is still low enough to allow ready mixing, heat transfer, and bubble elimination. Control of such polymerisations is relatively easy.
Bulk polymerisation of vinyl monomers is more difficult, since the reactions are highly exothermic and, with the usually thermally decomposed initiators, proceed at a rate that is strongly dependent on temperature. This, coulled with the problem in heat transfer incurred because viscosity increases early in the reaction, leads to difficulty in control and a tendency to development of a localised hot spot and runaways. Except in the preparation of the castings, for example, of poly(methyl methacrylate), bulk polymerisation is seldom used commercially for the manufacture of vinyl polymers.
Solution Polymeristion Polymerisation of vinyl monomers in solution is advantageous from the stand point of heat removal (e.g by allowing the solvent to reflux) and control, but has two potential disadvantages. First, the solvent must be selected with care to avoid chain transfer and second the polymer should be proferably be utailised in solution, as in the case of poly(vinyl acetate) to be converted to poly(vinyl alcohol) and some acrylic esters finishes. Since the complete removal of solvent from a polymer is often difficult to the point of impracticticality.