A process used for polymerizing ethylene to polyethylene and also for polymerizing propylene to polypropylene. Unlike the Ziegler–Natta process, it uses a gas phase process at low pressure. The catalyst is continuously added to the process and the granular product withdrawn. A co-monomer is also usually used in the process.
(p. 392) https://grace.com/en-us/capabilities/Pages/process-licensing.aspx Website for Dow Company’s UNIPOL process.