Molecular characterization of ultrahigh molar mass and soluble fractions of partially cross-linked polyethylenes

A reliable method is described for analyzing ultrahigh molar mass polyethylene (UHMW-PE) with a weight-average molar mass of 5700 kg/mol and molar mass fractions up to 50,000kg/mol by size exclusion chromatography (SEC) without molecular degradation as was proved by comparison of on-line and off-line viscometry. The use of low-bleed SEC columns (PLgel 20 mum Mixed-A LS), especially designed for on-line light-scattering detectors, allowed SEC to he coupled to a low-angle laser light-scattering detector without a filter ahead of the light-scattering cell. With this procedure, molded specimens of UHMW-PE, which are used for medical implants, such as hip endoprostheses, containing various amounts of a-tocopherol as a biocompatible stabilizer, were investigated. Furthermore, the effect of sterilization of the samples by gamma-irradiation (Co-60, 1.33 MeV, absorbed dose: 25 kGy) was studied with respect to the content of insoluble cross-linked material and the molar mass distribution of the soluble fraction.