ESR study of MMA polymerization by a peroxide/amine system: Bone cement formation

Electron spin resonance (ESR) spectroscopy was used to gain insight at the molecular level into the curing of bone cement. Methyl methacrylate was pol ymerized using a N,N-dimethyl-p-toluidine (TD)/benzoyl peroxide (BPO) redox system in the presence of polymethyl methacrylate (PMMA) powder. The conve ntional nine-lint ESR spectrum for the growing polymer radical was detected at the gel stage of polymerization. While the optimum free radical concent ration was observed near the equimolar amine/BPO concentration, Excess amin e led to a change in the chemical structure of the trapped radical and inhi bited the polymerization process. At a high amine/BPO ratio the nine-line s ignal disappeared and a three-line nitroxide-based radical appeared. The ap pearance of this nitroxide signal seems to depend on the amine/BPO molar ra tio and on the presence of PMMA. An excess amount of amine with respect to BPO was found to inhibit the polymerization process. When BPO was removed, the system still polymerized but with a longer gelation time and a lower ra dical concentration. These results demonstrate that trapped free radicals i n the bulk polymerization of MMA convert to polymeric peroxides that act as initiators in bone cement. When the accelerator 4-dimethylamino phenethyl alcohol (TDOH) was used, a higher radical concentration was observed in the polymerizing system. TDOH shows potential for being a more effective accel erator than TD for bone cement curing. (C) 1999 John Wiley & Sons, Inc.