Chapter 29 - ESR Insights into Macroradicals in UHMWPE

Abstract

Electron spin resonance (ESR) is a technique that can directly detect and quantify unpaired or odd electrons in atomic or molecular systems. ESR is the only technique that is particularly suitable, not only for direct detection, but also for quantitative analyses of free radicals in a solid or fluid. In polymers, free radicals are generally formed as a result of the unpairing of electrons from a particular molecular site (chain, side, or ring) by mechanical or chemical means, or by irradiation with ionizing radiation. The possession of an unpaired electron makes the free radical a good candidate for ESR study. The materials that contain unpaired electrons are known as paramagnetic materials because they exhibit a net magnetic moment in an external magnetic field. For this reason, ESR is also known as EPR or electron paramagnetic resonance. This chapter reveals that ultra-high molecular weight polyethylene (UHMWPE) has gained its importance in orthopedic science and technology for more than 5 decades as a material of choice for total hip- and knee-joint components. However, the physical and chemical properties of UHMWPE are adversely affected by free radicals that are generated in the polymer matrix as a result of radiation sterilization or crosslinking.