Preparation of Bis-GMA monomer which does not release bisphenol A

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The aim of the present investigation was to confirm the safety of Bis-GMA monomer by removing bisphenol A (BPA) from the monomer paying attention of the radical scavenging ability of BPA.1.Radical scavenging reaction with poly(methyl methacrylate) (PMMA)The amount of radical remaining in PMMA was related to its glass transition temperature and the amount was adjustable with heating. Copolymers of methacrylate monomer with MMA was prepared to enhance the solubility of polymers in Bis-GMA. The radical scavenging reaction with these copolymers could not remove BPA completely.2.Radical scavenging reaction with precursor of radicalTaking into account the solubility in Bis-GMA, low molecular weight precursors of radical, initiator system of visible light and heat polymerization, were used. Radical forming system by heat was not able to remove BPA successfully resulting in the heat polymerization of Bis-GMA. On the other hand, radical forming system by visible light irradiation was able to control both radical scavenging reaction and polymerization by adjusting the concentration of precursor of radical and the intensity of light irradiation.3.Removal of BPA by chromatographyThe main monomer component of Bis-GMA was purified by silica gel column chromatography treatment of commercial Bis-GMA product to examine the chemical reactivity of pure Bis-GMA. The addition of a precursor of radical, copolymer or initiator into pure Bis-GMA did not produce BPA, which indicated that dental products containing Bis-GMA never exert a harmful effect such as release of BPA once BPA was removed. It was also suggested in the process of the purification of Bis-GMA that BPA can be removed by adsorbents.