A polymer composite comprised of polyethylene (PE) and poly(vinyl acetate) (PVAc) with a biocompatible surface was developed for use in medical devices by the use of the following two-step processes: (i) the first step was to prepare polymer composite using supercritical carbon dioxide (ScCO2) methods and (ii) the second step was to introduce phosphorylcholine groups onto the surface of polymer composite by Surface reaction. This article especially reports a detailed study of the syntheses, and mechanical properties and the microstructure of obtained polymer composite by ScCO2 methods. The formation mechanism of PE/PVAc composites was that supercritical impregnation of a monomer and initiator into polymer substrate followed by in situ polymerization within the polymer matrix. Differential scanning calorimetry, wide-angle and small-angle X-ray scattering measurement showed that PE and PVAc were blended at the nanometer level. PVAc generated in the amorphous regions at nanometer level did not affect the crystalline of PE. This microstructure affected mechanical properties Such as dynamic viscoelasticity, Young's modulus, fracture stress and strain of the PE/PVAc composite. These properties depended on the composition of the composite that can be controlled with polymerization time. The synthesis method of polymer composite Using ScCO2 can be applied to create polymer biomaterials with suitable mechanical properties for the Soft tissue, hard tissue, and organs. (C) 2007 Elsevier B.V. All rights reserved.