Compare different polymerization methods: solution, slurry, gas phase, and high-pressure.

Solution polymerization - polymer dissolves in solvent, good heat transfer, used for EPDM, some LDPE. Slurry (suspension) - polymer as solid particles in diluent (hexane), good temperature control, used for HDPE, PP; requires polymer/diluent separation. Gas phase - polymer forms on catalyst in fluidized bed of polymer particles, no solvent, simpler recovery, used for HDPE, LLDPE, PP. High pressure - liquid phase at 1000-3000 bar, free radical mechanism, used for LDPE; distinctive branched structure. Selection factors: polymer type and properties, economics (solvent handling costs), heat removal capability, and flexibility. Many modern plants use gas phase (Unipol, Innovene) or slurry loop (Chevron Phillips) for simplicity and environmental benefits.