3-14a Polyethylene Radical chain polymerization of ethylene to polyethylene is carried out at high pressures of 120-300 MPa (7,000 43.000 psi) and at temperatures above the Tim of polyethylene (Fig. 3-18) [Doak, 1986]. Batch processes are not useful since the long residence time gives relatively poor control of product properties. Long-chain branching due to intermolecular chain transfer becomes excessive with deleterious effects on the physical properties. Continuous processes allow better control of the polymerization.