There isn't a problem with solvent removal and recovery that is associated with solution polymerization. There is an added drying step and this process does not readily lend itself to a continuous operation. The polymerization is carried out batch-wise in a stirred reactor which is jacketed for heating and cooling. I'm missing page 83 of the notes which should go here. Expanded polystyrene is very important as a thermal insulating material.
Most commercial methods make use of expandable beads.
Styrene is polymerized as it is in solution polymerization except that a low boiling point hydrocarbon such as n-pentane is added to the system. The alternative is to treat formed PS beads under heat and pressure with the volatile hydrocarbon. The impregnated beads are then expanded commonly by treatment with steam. When the beads are heated in the steam, they soften and volatilization of the low boiling point hydrocarbon and difusion of steam into the beads causes the beads to expand to about 40 times their original size. At this stage the beads aren't fused together.