Grafting of Polyurethane Surfaces with Poly(Ethylene Glycol)

Films of a commercial poly (ether urethane), Pellethane 2363-80AE, were prepared through solvent casting from dimethyl formamide. The films were grafted with poly (ethylene glycol) (PEG) by a two-step procedure. In the first step, the film surfaces were treated with hexamethylene diisocyanate in toluene in the presence of triethylamine as a catalyst. In the second step, PEG 1500 was allowed to react in toluene with surface bound isocyanate groups. It was shown by ATR-IR, XPS, and contact angle measurements that the grafted surfaces were mainly composed of PEG, and that they were strongly hydrophilic. It was also shown that unreacted PEG was entrapped in the material, which influenced its mechanical and thermal properties. Extraction of the films with toluene eliminated the entrapped PEG, and the hydrophilicity as well as the PEG coverage of the surface decreased. However, a subsequent treatment with aqueous NaCl solution induced a molecular restructuring of the surface, increasing the amount of grafted PEG at the surface to a value close to the original one.