If the heat energy cannot be dissipated, temperature rises, and at higher temperatures the reaction is going to go faster, so this is a positive feedback loop with disastrous consequences. For bulk polymerization , removal of unreacted monomer can be a problem. This is a large concern if your safe polymer was prepared from monomers which are toxic. Dimerization termination is more likely, and the rate of chain transfer is faster. For some condensation polymerizations, you can drive the condensation by-product from the reaction by azeotrope.
Suspension polymerization is used only in free radical type processes.
The monomer is mechanically dispersed in a media, usually water. There are cases where an organic media is used in which neither the polymer nor the monomer are soluble in the organic media. Usually the initiator is organic soluble. There are two separate phases throughout the whole process. The droplets must be kept far apart.