The production of Linear Low Density Polyethylene (LLDPE) involves polymerizing ethylene and other alpha-olefins in an inert solvent. Once the polymer is produced it is crystallized and pelletized. The newly formed pellets contain an unacceptable amount of solvent and residual co-monomer. This low molecular weight material must be removed in a further stage of de-volatilization. Design of equipment for performing this requires knowledge of the solubility and diffusion properties of low molecular weight solutes in semi-crystalline polyethylene. In this study the diffusion rates of 1-octene co-monomer and other low molecular weight substances in polyethylene pellets are predicted using the Vrentas-Duda free volume theory and compared with experimental data.