Abstract
In dentistry, a wide range of materials is available for restorative treatment; a typical product of such restorative materials mainly consists of radically polymerizable monomer(s) and inorganic filler(s) (for added physical strength), as well as a surface modifier (e.g. silane coupling agent) for improved affinity between monomer and filler. It is favorable to use an optimal surface modifier depending on the respective restorative materials. However, commercially available surface modifiers, which are synthesized by the ton, are not always suited for what is required for properties of the many different dental restorative materials. As a potential solution to such a problem, we focused on the latest technology, “micro flow reactors” that enabled an on-demand low-volume synthesis of many types of surface modifiers. Using micro reaction fields of such flow reactors, we synthesized a novel long-chain silane coupling agent. Compared to the control system synthesized using a conventional reaction flask, the novel system enabled significant reduction in reaction time without inducing any major side reactions. A dental composite resin that was treated with the novel coupling agent exhibited higher toughness, suggesting that such a silane coupling agent was an effective surface modifier.
Highlights
For industrial application, fillers used in composite resins are commonly surface-treated with silane couplingHow to cite this paper: Fuchigami, K., Fujimura, H., Teramae, M. and Nakatsuka, T. (2016) Precision Synthesis of a Long-Chain Silane Coupling Agent Using Micro Flow Reactors and Its Application in Dentistry
The urethanization reaction using the micro flow reactor 1 was completed in approx. 1.5 min at 75 ̊C, whereas by the conventional batch method with a reaction flask and a dropping funnel the reaction was not completed, with the raw materials left unreacted in the flask even at 8 h after completion of adding 2-isocyanatoethyl methacrylate
This suggested that molecules synthesized by the conventional batch method were exposed to heat for such an unnecessarily long period of time that urethane bonds formed were decomposed, which leads to high risks of side reactions and consequent yellowing of a precursor
Summary
Fillers used in composite resins are commonly surface-treated with silane coupling. Such a surface treatment improves affinity of filler for radically polymerizable monomers to increase filler content, and enhancing physical properties including compressive strength and flexural strength of a resulting composite resin. Γ-MPS has some drawbacks: due to its short alkylene chains, it cannot sufficiently hydrophobize the filler surface, and cannot give sufficient fracture toughness to a cured composite resin [8]; and has a low affinity for radically polymerizable monomers, such as urethane-based or glycidyl methacrylate-based binder resins, because γ-MPS has only one linking group, namely an ester group, in a molecule. Japan Patent No H2-134307 describes a method for synthesizing a long-chain (alkylene) silane coupling agent containing an ester group as an only linking group using reaction flasks. For the synthesis of L-SCA in the present study, we used micro flow reactors, as shown in Figure 3, to perform urethanization and hydrosilylation in a continuous manner in each micro reaction field of 32 μL, which substantially reduced side reactions as well as environmental burdens
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