Surface Physical Interpenetrating Networks of Poly(ethylene terephthalate) and Poly(ethylene oxide) with Biomedical Applications

Poly(ethylene terephthalate) (PET) films were modified by diffusing poly(ethylene oxide) (PEO) into the surface of the PET, which was swollen in a mutual solvent. Subsequent rapid deswelling in a nonsolvent for PET resulted in the stable entrapment of the PEO within the surface of the PET. The PET/PEO systems produced by this technique were phase-mixed nonequilibrium surface structures, kinetically stable below the T_g for PET. The surface-localized structure is referred to as a surface physical interpenetrating network (SPIN), due to the similarity of the forming technique to that for a sequential interpenetrating polymer network. Analyses of these materials by X-ray photoelectron spectroscopy (XPS) and NMR spectroscopy revealed PEO incoroporation as high as 23 mol % or 6.4 wt %, with a preferential localization of the PEO near the surface of the PET film. Differential scanning calorimetry (DSC) indicated a phasemixed structure, despite the thermodynamic incompatibility of PEO and PET, which could be induced to phase separate upon heating above the PET T_g. These materials were stable at 37 °C for several months in an aqueous environment, but PEO leaching occurred upon incubation in water at temperatures near the PET T_g as well as upon swelling the PET with organic solvents at room temperature. These materials have been previously shown by us to be extraordinarily resistant to cellular adhesion.