COMPARISON OF 2 ANTIOXIDANTS FOR POLY(ETHERURETHANE UREA) IN AN ACCELERATED IN-VITRO BIODEGRADATION SYSTEM

Vitamin E (+/-alpha-tocopherol) was recently investigated as an antiox idant for implanted poly(etherurethane urea) (PEUU) elastomers. In tha t work, vitamin E prevented chemical degradation of biaxially strained PEUU up to 5 weeks implantation, and prevented pitting and cracking o f the PEUU surface for the duration of the 10-week cage implant study. The promising results of the in vivo studies motivated a detailed com parison of vitamin E with Santowhite(R), the standard antioxidant used in PEUU elastomers. To evaluate vitamin E and Santowhite(R) as antiox idants in PEUU, an accelerated in vitro treatment system was used that mimics the in vivo degradation of PEUUs.(2-4) Vitamin E was even more effective than Santowhite(R) in preventing pitting and cracking to th e biaxially strained PEUU elastomers. The inhibition of ether oxidatio n was greater with vitamin E than with Santowhite(R) when compared by equivalent concentrations and molar concentrations, respectively. It i s hypothesized that the increased effectiveness of vitamin E in this s ystem, compared to Santowhite(R), is due to differences in antioxidant mechanism(s). Vitamin E is more efficient in preventing PEUU oxidatio n than Santowhite(R) because its phenoxy radical is more stable and it can terminate more than one chain per vitamin E molecule. (C) 1997 Jo hn Wiley & Sons, Inc.