Preparation And Characterization Of Novel Bis-Gma Derivates With Particular Structures And Coresponding Composites

Dental composite which was born in 1960s is a kind of important restorative materials for its excellent process ability, aesthetics and biocompatibility. The typical dental composite consists of a mixture of organic monomers, inorganic fillers and initiators. As the continuous phase, the monomers unite all the separate fillers and form the bone structure of composites after polymerization. Its performance affects the mechanical properties of the composites as well as the service properties.Bis-GMA is a kind of common used monomers for its excellent mechanical properties and reactivity. Due to the hydrogen bonding between hydroxyl groups in Bis-GMA, the viscosity of the monomer reaches to a high level that results in a large amount of diluents being introduced into the system to decrease the viscosity for better application. However, a number of adverse effects are coming with the diluents such as increased curing shrinkage. So synthesis of novel monomers is an important way to optimize the dental composites.In this research, three kinds of Bis-GMA derivates without hydroxyl groups have been synthesized to reduce the viscosity and increase the final conversion. The viscosities and reaction kinetics of novel monomers have been studied as well as the properties of corresponding composites with 70wt% inorganic fillers.(1) The involved acid chlorides include acetyl chloride, benzoyl chloride and valeroyl chloride. So the relevant derivates are acetylation Bis-GMA (Ac-Bis-GMA), benzoylation Bis-GMA (Bz-Bis-GMA) and valeroylation Bis-GMA (Vr-Bis-GMA).(2) The viscosities are rapidly decreased with the replacement of hydroxyl groups. The usual strategy is adding 50wt% TEGDMA into Bis-GMA to decrease viscosity. To get this viscosity, the necessary TEGDMA for Ac-Bis-GMA is 30wt% when the corresponding value for Bz-Bis-GMA and Vr-Bis-GMA is 20wt%.(3) The photo-polymerization kinetics of Bis-GMA and derivates are studied by DSC. It turn out to be that both the viscosity and mobility of monomers affect the final conversions. The highest final conversion value was achieved by Ac-Bis-GMA which has the highest mobility and lower viscosity. The mobility of Bz-Bis-GMA is seriously influenced by steric hindrance effect of benzoyl groups that result in the final conversion of Bz-Bis-GMA as the lowest one during four monomers. On this base, the relationship between ratio of TEGDMA and final conversions are also investigated. The results show that the final conversions are increased by the increased ratio of TEGDMA for each kind of derivates.(4) Corresponding composites of Bis-GMA, Ac-Bis-GMA, Bz-Bis-GMA and Vr-Bis-GMA are prepared by adding equal TEGDMA, inorganic fillers and initiators separately. The results of three-point bending and compressing test show that mechanical properties of composites are enhanced by intermolecular hydrogen bodings. So the flexural and compressive strength of Bis-GMA based composites are the highest. And the values for other three composites are ordered by corresponding final conversions. Shrinkage rates of composites are relevant with final conversion and size of monomers. Bz-Bis-GMA based composites get the lowest shrinkage rate for its lowest final conversion and biggest molecular. At last, the SEM images show the splendid organic/inorganic compatibilities of these four kinds of composites.