Effects of branching and molecular weight of surface-bound poly(ethylene oxide) on protein rejection.

To understand better the origin of protein rejection observed with surface-bound poly(ethylene oxide) (or PEO), we have measured fibrinogen adsorption for a series of linear and branched, low-molecular-weight PEOs bound to solid polystyrene surfaces. The results show that a dependence on molecular weight is found below 1500 g mol-1 for linear PEO. Branched PEOs are less effective at protein rejection than linear PEOs. The branched PEOs have smaller exclusion volumes (from GPC) than the corresponding linear PEOs, consistent with restriction in conformational freedom for the branched compounds. The protein rejection results are interpreted in terms of entropy changes that result upon protein adsorption. In addition, some practical problems in preparation of PEO glycidyl ethers have been clarified, thus making these PEO derivatives more useful for surface modification.