Diffusion coefficients (D) of polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) were determined by film-stacking technique in low-density polyethylene (LDPE) and two types of polydimethylsiloxane (PDMS) (also known as silicone rubber, SR) with the trade names AlteSil (TM) and Silastic. The estimated values of D for PCBs and PAHs over a wide range of hydrophobicity were 2-2.5 orders of magnitude lower in LDPE than in SR polymers. Log D (m(2) s(-1)) of PCBs ranged from -10.1 to -10.9 for SRs and from -12.4 to -13.7 for LDPE. For PAHs these ranges were -9.8 to -11.4 for SRs and -11.9 to -13.7 for LDPE. Compared with the D values calculated in water, D were 1-2 and 3-4 orders of magnitude lower in SR and LDPE, respectively. For PAH molecules, D was lower than for PCBs with a similar molecular weight, probably because of their more rigid structure. The range of log D for PCBs in SR was only 0.5 log units (factor of 3.2) versus 1.2 log units (factor of 16) in LDPE. Although compound classes showed different relations, a linear relation of D with total surface area was the most universal. This relation may be used for prediction of D values in SR and LDPE polymers for other organic compounds. (C) 201.0 Wiley Periodicals, Inc. J Appl Polym Sci 116: 1803-1810, 2010