Densely crosslinked semi-interpenetrating polymer networks (semi-IPNs) of poly(ethylene glycol) (PEG) were synthesized by photopolymerizing a melt of PEG of various molecular weights and end-group functionalities in neat trimethylolpropane triacrylate (TMPTA). Increasing the molecular weight of PEG in the matrix from 1000 to 100,000 g/mol reduced the advancing and receding contact angles, contact angle hysteresis, and adsorption of human fibrinogen and bovine serum albumin. Crosslinked TMPTA homonetworks supported human fibroblast adhesion in vitro, whereas the resistance to cell adhesion of the semi-IPNs depended upon PEG molecular weight: Lower molecular weight PEG reduced the number of adherent cells; higher molecular weight PEG further reduced and eliminated cell adhesion, as did networks containing acrylate-functionalized PEG. A polymer system incorporated with PEG throughout a hydrophobic, densely crosslinked matrix, rather than as a blend or surface treatment, may be particularly useful for limiting biologic interactions when bulk material properties must be independent of the solvent environment and where surface abrasion may occur. © 1995 John Wiley & Sons, Inc.